Learn to parse CSV (Comma Separated Values) files with Python examples using the csv module's reader function and DictReader class.

Sometimes it is useful to “backcast” a time series — that is, forecast in reverse time. Although there are no in-built R functions to do this, it is very easy to implement. Suppose x is our time series and we want to backcast for periods. Here is some code that should work for most univariate time series. The example is non-seasonal, but the code will also work with seasonal data. library(forecast) x <- WWWusage h <- 20 f <- frequency(x) # Reverse time revx <- ts(rev(x), frequency=f) # Forecast fc <- forecast(auto.arima(revx), h) plot(fc) # Reverse time again fc$mean <- ts(rev(fc$mean),end=tsp(x)[1] - 1/f, frequency=f) fc$upper <- fc$upper[h:1,] fc$lower <- fc$lower[h:1,] fc$x <- x # Plot result plot(fc, xlim=c(tsp(x)[1]-h/f, tsp(x)[2]))

Within this post we will have a deeper look into the new Date/Time API we get with Java 8 (JSR 310). Please note that this post is mainly driven by code examples that show the new API functionality. I think the examples are self-explanatory so I did not spent much time writing text around them :-) Let's get started! Working with Date and Time Objects All classes of the Java 8 Date/Time API are located within the java.time package. The first class we want to look at is java.time.LocalDate. A LocalDate represents a year-month-day date without time. We start with creating new LocalDate instances: // the current date LocalDate currentDate = LocalDate.now(); // 2014-02-10 LocalDate tenthFeb2014 = LocalDate.of(2014, Month.FEBRUARY, 10); // months values start at 1 (2014-08-01) LocalDate firstAug2014 = LocalDate.of(2014, 8, 1); // the 65th day of 2010 (2010-03-06) LocalDate sixtyFifthDayOf2010 = LocalDate.ofYearDay(2010, 65); LocalTime and LocalDateTime are the next classes we look at. Both work similar to LocalDate. ALocalTime works with time (without dates) while LocalDateTime combines date and time in one class: LocalTime currentTime = LocalTime.now(); // current time LocalTime midday = LocalTime.of(12, 0); // 12:00 LocalTime afterMidday = LocalTime.of(13, 30, 15); // 13:30:15 // 12345th second of day (03:25:45) LocalTime fromSecondsOfDay = LocalTime.ofSecondOfDay(12345); // dates with times, e.g. 2014-02-18 19:08:37.950 LocalDateTime currentDateTime = LocalDateTime.now(); // 2014-10-02 12:30 LocalDateTime secondAug2014 = LocalDateTime.of(2014, 10, 2, 12, 30); // 2014-12-24 12:00 LocalDateTime christmas2014 = LocalDateTime.of(2014, Month.DECEMBER, 24, 12, 0); By default LocalDate/Time classes will use the system clock in the default time zone. We can change this by providing a time zone or an alternative Clock implementation: // current (local) time in Los Angeles LocalTime currentTimeInLosAngeles = LocalTime.now(ZoneId.of("America/Los_Angeles")); // current time in UTC time zone LocalTime nowInUtc = LocalTime.now(Clock.systemUTC()); From LocalDate/Time objects we can get all sorts of useful information we might need. Some examples: LocalDate date = LocalDate.of(2014, 2, 15); // 2014-06-15 boolean isBefore = LocalDate.now().isBefore(date); // false // information about the month Month february = date.getMonth(); // FEBRUARY int februaryIntValue = february.getValue(); // 2 int minLength = february.minLength(); // 28 int maxLength = february.maxLength(); // 29 Month firstMonthOfQuarter = february.firstMonthOfQuarter(); // JANUARY // information about the year int year = date.getYear(); // 2014 int dayOfYear = date.getDayOfYear(); // 46 int lengthOfYear = date.lengthOfYear(); // 365 boolean isLeapYear = date.isLeapYear(); // false DayOfWeek dayOfWeek = date.getDayOfWeek(); int dayOfWeekIntValue = dayOfWeek.getValue(); // 6 String dayOfWeekName = dayOfWeek.name(); // SATURDAY int dayOfMonth = date.getDayOfMonth(); // 15 LocalDateTime startOfDay = date.atStartOfDay(); // 2014-02-15 00:00 // time information LocalTime time = LocalTime.of(15, 30); // 15:30:00 int hour = time.getHour(); // 15 int second = time.getSecond(); // 0 int minute = time.getMinute(); // 30 int secondOfDay = time.toSecondOfDay(); // 55800 Some information can be obtained without providing a specific date. For example, we can use the Year class if we need information about a specific year: Year currentYear = Year.now(); Year twoThousand = Year.of(2000); boolean isLeap = currentYear.isLeap(); // false int length = currentYear.length(); // 365 // sixtyFourth day of 2014 (2014-03-05) LocalDate date = Year.of(2014).atDay(64); We can use the plus and minus methods to add or subtract specific amounts of time. Note that these methods always return a new instance (Java 8 date/time classes are immutable). LocalDate tomorrow = LocalDate.now().plusDays(1); // before 5 houres and 30 minutes LocalDateTime dateTime = LocalDateTime.now().minusHours(5).minusMinutes(30); TemporalAdjusters are another nice way for date manipulation. TemporalAdjuster is a single method interface that is used to separate the process of adjustment from actual date/time objects. A set of common TemporalAdjusters can be accessed using static methods of the TemporalAdjusters class. LocalDate date = LocalDate.of(2014, Month.FEBRUARY, 25); // 2014-02-25 // first day of february 2014 (2014-02-01) LocalDate firstDayOfMonth = date.with(TemporalAdjusters.firstDayOfMonth()); // last day of february 2014 (2014-02-28) LocalDate lastDayOfMonth = date.with(TemporalAdjusters.lastDayOfMonth()); Static imports make this more fluent to read: import static java.time.temporal.TemporalAdjusters.*; ... // last day of 2014 (2014-12-31) LocalDate lastDayOfYear = date.with(lastDayOfYear()); // first day of next month (2014-03-01) LocalDate firstDayOfNextMonth = date.with(firstDayOfNextMonth()); // next sunday (2014-03-02) LocalDate nextSunday = date.with(next(DayOfWeek.SUNDAY)); Time Zones Working with time zones is another big topic that is simplified by the new API. The LocalDate/Time classes we have seen so far do not contain information about a time zone. If we want to work with a date/time in a certain time zone we can use ZonedDateTime or OffsetDateTime: ZoneId losAngeles = ZoneId.of("America/Los_Angeles"); ZoneId berlin = ZoneId.of("Europe/Berlin"); // 2014-02-20 12:00 LocalDateTime dateTime = LocalDateTime.of(2014, 02, 20, 12, 0); // 2014-02-20 12:00, Europe/Berlin (+01:00) ZonedDateTime berlinDateTime = ZonedDateTime.of(dateTime, berlin); // 2014-02-20 03:00, America/Los_Angeles (-08:00) ZonedDateTime losAngelesDateTime = berlinDateTime.withZoneSameInstant(losAngeles); int offsetInSeconds = losAngelesDateTime.getOffset().getTotalSeconds(); // -28800 // a collection of all available zones Set allZoneIds = ZoneId.getAvailableZoneIds(); // using offsets LocalDateTime date = LocalDateTime.of(2013, Month.JULY, 20, 3, 30); ZoneOffset offset = ZoneOffset.of("+05:00"); // 2013-07-20 03:30 +05:00 OffsetDateTime plusFive = OffsetDateTime.of(date, offset); // 2013-07-19 20:30 -02:00 OffsetDateTime minusTwo = plusFive.withOffsetSameInstant(ZoneOffset.ofHours(-2)); Timestamps Classes like LocalDate and ZonedDateTime provide a human view on time. However, often we need to work with time viewed from a machine perspective. For this we can use the Instant class which represents timestamps. An Instant counts the time beginning from the first second of January 1, 1970 (1970-01-01 00:00:00) also called the EPOCH. Instant values can be negative if they occured before the epoch. They followISO 8601 the standard for representing date and time. // current time Instant now = Instant.now(); // from unix timestamp, 2010-01-01 12:00:00 Instant fromUnixTimestamp = Instant.ofEpochSecond(1262347200); // same time in millis Instant fromEpochMilli = Instant.ofEpochMilli(1262347200000l); // parsing from ISO 8601 Instant fromIso8601 = Instant.parse("2010-01-01T12:00:00Z"); // toString() returns ISO 8601 format, e.g. 2014-02-15T01:02:03Z String toIso8601 = now.toString(); // as unix timestamp long toUnixTimestamp = now.getEpochSecond(); // in millis long toEpochMillis = now.toEpochMilli(); // plus/minus methods are available too Instant nowPlusTenSeconds = now.plusSeconds(10); Periods and Durations Period and Duration are two other important classes. Like the names suggest they represent a quantity or amount of time. A Period uses date based values (years, months, days) while a Duration uses seconds or nanoseconds to define an amount of time. Duration is most suitable when working with Instants and machine time. Periods and Durations can contain negative values if the end point occurs before the starting point. // periods LocalDate firstDate = LocalDate.of(2010, 5, 17); // 2010-05-17 LocalDate secondDate = LocalDate.of(2015, 3, 7); // 2015-03-07 Period period = Period.between(firstDate, secondDate); int days = period.getDays(); // 18 int months = period.getMonths(); // 9 int years = period.getYears(); // 4 boolean isNegative = period.isNegative(); // false Period twoMonthsAndFiveDays = Period.ofMonths(2).plusDays(5); LocalDate sixthOfJanuary = LocalDate.of(2014, 1, 6); // add two months and five days to 2014-01-06, result is 2014-03-11 LocalDate eleventhOfMarch = sixthOfJanuary.plus(twoMonthsAndFiveDays); // durations Instant firstInstant= Instant.ofEpochSecond( 1294881180 ); // 2011-01-13 01:13 Instant secondInstant = Instant.ofEpochSecond(1294708260); // 2011-01-11 01:11 Duration between = Duration.between(firstInstant, secondInstant); // negative because firstInstant is after secondInstant (-172920) long seconds = between.getSeconds(); // get absolute result in minutes (2882) long absoluteResult = between.abs().toMinutes(); // two hours in seconds (7200) long twoHoursInSeconds = Duration.ofHours(2).getSeconds(); Formatting and Parsing Formatting and parsing is another big topic when working with dates and times. In Java 8 this can be accomplished by using the format() and parse() methods: // 2014-04-01 10:45 LocalDateTime dateTime = LocalDateTime.of(2014, Month.APRIL, 1, 10, 45); // format as basic ISO date format (20140220) String asBasicIsoDate = dateTime.format(DateTimeFormatter.BASIC_ISO_DATE); // format as ISO week date (2014-W08-4) String asIsoWeekDate = dateTime.format(DateTimeFormatter.ISO_WEEK_DATE); // format ISO date time (2014-02-20T20:04:05.867) String asIsoDateTime = dateTime.format(DateTimeFormatter.ISO_DATE_TIME); // using a custom pattern (01/04/2014) String asCustomPattern = dateTime.format(DateTimeFormatter.ofPattern("dd/MM/yyyy")); // french date formatting (1. avril 2014) String frenchDate = dateTime.format(DateTimeFormatter.ofPattern("d. MMMM yyyy", new Locale("fr"))); // using short german date/time formatting (01.04.14 10:45) DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT) .withLocale(new Locale("de")); String germanDateTime = dateTime.format(formatter); // parsing date strings LocalDate fromIsoDate = LocalDate.parse("2014-01-20"); LocalDate fromIsoWeekDate = LocalDate.parse("2014-W14-2", DateTimeFormatter.ISO_WEEK_DATE); LocalDate fromCustomPattern = LocalDate.parse("20.01.2014", DateTimeFormatter.ofPattern("dd.MM.yyyy")); Conversion Of course we do not always have objects of the type we need. Therefore, we need an option to convert different date/time related objects between each other. The following examples show some of the possible conversion options: // LocalDate/LocalTime <-> LocalDateTime LocalDate date = LocalDate.now(); LocalTime time = LocalTime.now(); LocalDateTime dateTimeFromDateAndTime = LocalDateTime.of(date, time); LocalDate dateFromDateTime = LocalDateTime.now().toLocalDate(); LocalTime timeFromDateTime = LocalDateTime.now().toLocalTime(); // Instant <-> LocalDateTime Instant instant = Instant.now(); LocalDateTime dateTimeFromInstant = LocalDateTime.ofInstant(instant, ZoneId.of("America/Los_Angeles")); Instant instantFromDateTime = LocalDateTime.now().toInstant(ZoneOffset.ofHours(-2)); // convert old date/calendar/timezone classes Instant instantFromDate = new Date().toInstant(); Instant instantFromCalendar = Calendar.getInstance().toInstant(); ZoneId zoneId = TimeZone.getDefault().toZoneId(); ZonedDateTime zonedDateTimeFromGregorianCalendar = new GregorianCalendar().toZonedDateTime(); // convert to old classes Date dateFromInstant = Date.from(Instant.now()); TimeZone timeZone = TimeZone.getTimeZone(ZoneId.of("America/Los_Angeles")); GregorianCalendar gregorianCalendar = GregorianCalendar.from(ZonedDateTime.now()); Conclusion With Java 8 we get a very rich API for working with date and time located in the java.time package. The API can completely replace old classes like java.util.Date or java.util.Calendar with newer, more flexible classes. Due to mostly immutable classes the new API helps in building thread safe systems. The source of the examples can be found on GitHub.

First of all, let me tell this out loud: Spring is no longer XML-heavy. As a matter of fact you can write Spring applications these days with minimal or no XML at all, using plenty of annotations, Java configuration and Spring Boot. Seriously stop ranting about Spring and XML, it's the thing the of the past. That being said you might still be using XML for couple of reasons: you are stuck with legacy code base, you chose XML for other reasons or you use Spring as a foundation for some framework/platform. The last case is actually quite common, for example Mule ESB and ActiveMQ use Spring underneath to wire up their dependencies. Moreover Spring XML is their way to configure the framework. However configuring message broker or enterprise service bus using plain Spring s would be cumbersome and verbose. Luckily Spring supports writing custom namespaces that can be embedded within standard Spring configuration files. These custom snippets of XML are preprocessed at runtime and can register many bean definitions at once in a concise and pleasantly looking (as far as XML allows) format. In a way custom namespaces are like macros that expand at runtime into multiple bean definitions. To give you a feeling of what are we aiming at, imagine a standard "enterprise" application that has several business entities. For each entity we define three, almost identical, beans: repository, service and controller. They are always wired in a similar way and only differ in small details. To begin with, our Spring XML looks like this (I am pasting screenshot with thumbnail to spare your eyes, it's huge and bloated): This is a "layered" architecture, thus we will call our custom namespace called onion - because onions have layers - and also because systems designed this way make me cry. By the end of this article you will learn how to collapse this pile of XML into: Look closely, it's still Spring XML file that is perfectly understandable by this framework - and you will learn how to achieve this. You can run arbitrary code for each top-level custom XML tag, e.g. single occurrence of registers repository, service and controller bean definitions all at once. The first thing to implement is writing a custom XML schema for our namespace. This is not that hard and will allow IntelliJ IDEA to show code completion in XML: Once the schema is completed we must register it in Spring using two files: /META-INF/spring.schemas: http\://nurkiewicz.blogspot.com/spring/onion/spring-onion.xsd=/com/blogspot/nurkiewicz/onion/ns/spring-onion.xsd /META-INF/spring.handlers: http\://nurkiewicz.blogspot.com/spring/onion/spring-onion.xsd=com.blogspot.nurkiewicz.onion.ns.OnionNamespaceHandler One maps schema URL into schema location locally, another points to so-called namespace handler. This class is fairly straightforward - it tells what to do with every top-level custom XML tag coming from this namespace encountered in Spring configuration file: import org.springframework.beans.factory.xml.NamespaceHandlerSupport; public class OnionNamespaceHandler extends NamespaceHandlerSupport { public void init() { registerBeanDefinitionParser("entity", new EntityBeanDefinitionParser()); registerBeanDefinitionParser("converter", new ConverterBeanDefinitionParser()); } } So, when piece of XML is found by Spring, it knows that our ConverterBeanDefinitionParser needs to be used. Remember that if our custom tag has children (like in the case of ), bean definition parser is called only for top-level tag. It is up to us how we parse and handle children. OK, so single tag is suppose to create the following two beans: The responsibility of bean definition parser is to programmatically register bean definitions otherwise defined in XML. I won't go into details of the API, but compare it with the XML snippet above, they match closely to each other: import org.w3c.dom.Element; public class ConverterBeanDefinitionParser extends AbstractBeanDefinitionParser { @Override protected AbstractBeanDefinition parseInternal(Element converterElement, ParserContext parserContext) { final String format = converterElement.getAttribute("format"); final String lenientStr = converterElement.getAttribute("lenient"); final boolean lenient = lenientStr != null? Boolean.valueOf(lenientStr) : true; final BeanDefinitionRegistry registry = parserContext.getRegistry(); final AbstractBeanDefinition converterBeanDef = converterBeanDef(format, lenient); registry.registerBeanDefinition(format + "Converter", converterBeanDef); final AbstractBeanDefinition readerBeanDef = readerBeanDef(format); registry.registerBeanDefinition(format + "Reader", readerBeanDef); return null; } private AbstractBeanDefinition readerBeanDef(String format) { return BeanDefinitionBuilder. rootBeanDefinition(ReaderFactoryBean.class). addPropertyValue("format", format). getBeanDefinition(); } private AbstractBeanDefinition converterBeanDef(String format, boolean lenient) { AbstractBeanDefinition converterBeanDef = BeanDefinitionBuilder. rootBeanDefinition(Converter.class.getName()). addConstructorArgValue(format + ".xml"). addConstructorArgValue(lenient). addPropertyReference("reader", format + "Reader"). getBeanDefinition(); converterBeanDef.setFactoryBeanName("convertersFactory"); converterBeanDef.setFactoryMethodName("build"); return converterBeanDef; } } Do you see how parseInternal() receives XML Element representing tag, extracts attributes and registers bean definitions? It's up to you how many beans you define in AbstractBeanDefinitionParser implementation. Just remember that we are barely constructing the configuration here, no instantiation took place yet. Once the XML file is fully parsed and all bean definition parsers triggered, Spring will start bootstrapping our application. One thing to keep in mind is returning null in the end. The API sort of expects you to return single bean definition. However no need to restrict ourselves, null is fine. The second custom tag that we support is that registers three beans at once. It's similar and thus not that interesting, see full source of EntityBeanDefinitionParser. One important implementation detail that can be found there is the usage of ManagedList. Documentation vaguely mentions it but it's quite valuable. If you want to define a list of beans to be injected knowing their IDs, a simple List is not sufficient, you must explicitly tell Spring you mean a list of bean references: List converterRefs = new ManagedList<>(); for (String converterName : converters) { converterRefs.add(new RuntimeBeanReference(converterName)); } return BeanDefinitionBuilder. rootBeanDefinition("com.blogspot.nurkiewicz.FooService"). addPropertyValue("converters", converterRefs). getBeanDefinition(); Using JAXB to simplify bean definition parsers OK, so by now you should be familiar with custom Spring namespaces and how they can help you. However they are quite low level by requiring you to parse custom tags using raw XML DOM API. However my team mate discovered that since we already have XSD schema file, why not use JAXB to handle XML parsing? First we ask maven to generate Java beans representing XML types and elements during build: org.jvnet.jaxb2.maven2 maven-jaxb22-plugin 0.8.3 xjc generate src/main/resources/com/blogspot/nurkiewicz/onion/ns com.blogspot.nurkiewicz.onion.ns.xml Under /target/generated-sources/xjc you will discover couple of Java files. I like generated JAXB models to have some commons prefix like Xml, which can be easily achieved with custom bindings.xjb file placed next to spring-onion.xsd: How does it change our custom bean definition parser? Previously we had this: final String clazz = entityElement.getAttribute("class"); //... final NodeList pageNodes = entityElement.getElementsByTagNameNS(NS, "page"); for (int i = 0; i < pageNodes.getLength(); ++i) { //...final String clazz = entityElement.getAttribute("class"); //... final NodeList pageNodes = entityElement.getElementsByTagNameNS(NS, "page"); for (int i = 0; i < pageNodes.getLength(); ++i) { //... Now we simply traverse Java beans: final XmlEntity entity = JaxbHelper.unmarshal(entityElement); final String clazz = entity.getClazz(); //... for (XmlPage page : entity.getPage()) { //... JaxbHelper is just a simple tool that hides checked exceptions and JAXB mechanics from outside: public class JaxbHelper { private static final Unmarshaller unmarshaller = create(); private static Unmarshaller create() { try { return JAXBContext.newInstance("com.blogspot.nurkiewicz.onion.ns.xml").createUnmarshaller(); } catch (JAXBException e) { throw Throwables.propagate(e); } } public static T unmarshal(Element elem) { try { return (T) unmarshaller.unmarshal(elem); } catch (JAXBException e) { throw Throwables.propagate(e); } } } Couple of words as a summary. First of all I don't encourage you to auto-generate repository/service/controller bean definitions for every entity. Actually it's a poor practice but the domain is familiar to all of us so I thought it will be a good example. Secondly, more important, custom XML namespaces are a powerful tool that should be used as a last resort when everything else fails, namely abstract beans, factory beans and Java configuration. Typically you'll want this kind of feature in frameworks or tools built in top of Spring. In that case check out full source code on GitHub.

We all write unit tests but the challenge we face at times is that the unit under test might be dependent on other components. And configuring other components for unit testing is definitely an overkill. Instead we can make use of Mocks in place of the other components and continue with the unit testing. To show how one can use mocks, I have a Data access layer(DAL), basically a class which provides an API for the application to access and modify the data in the data repository. I then unit test the DAL without actually the need to connect to the data repository. The data repository can be a local database or remote database or a file system or any place where we can store and retrieve the data. The use of a DAL class helps us in keeping the data mappers separate from the application code. Lets create a Java project using maven. mvn archetype:generate -DgroupId=info.sanaulla -DartifactId=MockitoDemo -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false The above creates a folder MockitoDemo and then creates the entire directory structure for source and test files. Consider the below model class for this example: package info.sanaulla.models; import java.util.List; /** * Model class for the book details. */ public class Book { private String isbn; private String title; private List authors; private String publication; private Integer yearOfPublication; private Integer numberOfPages; private String image; public Book(String isbn, String title, List authors, String publication, Integer yearOfPublication, Integer numberOfPages, String image){ this.isbn = isbn; this.title = title; this.authors = authors; this.publication = publication; this.yearOfPublication = yearOfPublication; this.numberOfPages = numberOfPages; this.image = image; } public String getIsbn() { return isbn; } public String getTitle() { return title; } public List getAuthors() { return authors; } public String getPublication() { return publication; } public Integer getYearOfPublication() { return yearOfPublication; } public Integer getNumberOfPages() { return numberOfPages; } public String getImage() { return image; } } The DAL class for operating on the Book model class is: package info.sanaulla.dal; import info.sanaulla.models.Book; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; /** * API layer for persisting and retrieving the Book objects. */ public class BookDAL { private static BookDAL bookDAL = new BookDAL(); public List getAllBooks(){ return Collections.EMPTY_LIST; } public Book getBook(String isbn){ return null; } public String addBook(Book book){ return book.getIsbn(); } public String updateBook(Book book){ return book.getIsbn(); } public static BookDAL getInstance(){ return bookDAL; } } The DAL layer above currently has no functionality and we are going to unit test that piece of code (TDD). The DAL layer might communicate with a ORM Mapper or Database API which we are not concerned while designing the API. Test Driving the DAL Layer There are lot of frameworks for Unit testing and mocking in Java but for this example I would be picking JUnit for unit testing and Mockito for mocking. We would have to update the dependency in Maven’s pom.xml 4.0.0 info.sanaulla MockitoDemo jar 1.0-SNAPSHOT MockitoDemo http://maven.apache.org junit junit 4.10 test org.mockito mockito-all 1.9.5 test Now lets unit test the BookDAL. During the unit testing we will inject mock data into the BookDAL so that we can complete the testing of the API without depending on the data source. Initially we will have an empty test class: public class BookDALTest { public void setUp() throws Exception { } public void testGetAllBooks() throws Exception { } public void testGetBook() throws Exception { } public void testAddBook() throws Exception { } public void testUpdateBook() throws Exception { } } We will inject the mock BookDAL and mock data in the setUp() as shown below: public class BookDALTest { private static BookDAL mockedBookDAL; private static Book book1; private static Book book2; @BeforeClass public static void setUp(){ //Create mock object of BookDAL mockedBookDAL = mock(BookDAL.class); //Create few instances of Book class. book1 = new Book("8131721019","Compilers Principles", Arrays.asList("D. Jeffrey Ulman","Ravi Sethi", "Alfred V. Aho", "Monica S. Lam"), "Pearson Education Singapore Pte Ltd", 2008,1009,"BOOK_IMAGE"); book2 = new Book("9788183331630","Let Us C 13th Edition", Arrays.asList("Yashavant Kanetkar"),"BPB PUBLICATIONS", 2012,675,"BOOK_IMAGE"); //Stubbing the methods of mocked BookDAL with mocked data. when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2)); when(mockedBookDAL.getBook("8131721019")).thenReturn(book1); when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn()); when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn()); } public void testGetAllBooks() throws Exception {} public void testGetBook() throws Exception {} public void testAddBook() throws Exception {} public void testUpdateBook() throws Exception {} } In the above setUp() method I have: Created a mock object of BookDAL BookDAL mockedBookDAL = mock(BookDAL.class); Stubbed the API of BookDAL with mock data, such that when ever the API is invoked the mocked data is returned. //When getAllBooks() is invoked then return the given data and so on for the other methods. when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2)); when(mockedBookDAL.getBook("8131721019")).thenReturn(book1); when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn()); when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn()); Populating the rest of the tests we get: package info.sanaulla.dal; import info.sanaulla.models.Book; import org.junit.BeforeClass; import org.junit.Test; import static org.junit.Assert.*; import static org.mockito.Mockito.mock; import static org.mockito.Mockito.when; import java.util.Arrays; import java.util.List; public class BookDALTest { private static BookDAL mockedBookDAL; private static Book book1; private static Book book2; @BeforeClass public static void setUp(){ mockedBookDAL = mock(BookDAL.class); book1 = new Book("8131721019","Compilers Principles", Arrays.asList("D. Jeffrey Ulman","Ravi Sethi", "Alfred V. Aho", "Monica S. Lam"), "Pearson Education Singapore Pte Ltd", 2008,1009,"BOOK_IMAGE"); book2 = new Book("9788183331630","Let Us C 13th Edition", Arrays.asList("Yashavant Kanetkar"),"BPB PUBLICATIONS", 2012,675,"BOOK_IMAGE"); when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2)); when(mockedBookDAL.getBook("8131721019")).thenReturn(book1); when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn()); when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn()); } @Test public void testGetAllBooks() throws Exception { List allBooks = mockedBookDAL.getAllBooks(); assertEquals(2, allBooks.size()); Book myBook = allBooks.get(0); assertEquals("8131721019", myBook.getIsbn()); assertEquals("Compilers Principles", myBook.getTitle()); assertEquals(4, myBook.getAuthors().size()); assertEquals((Integer)2008, myBook.getYearOfPublication()); assertEquals((Integer) 1009, myBook.getNumberOfPages()); assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication()); assertEquals("BOOK_IMAGE", myBook.getImage()); } @Test public void testGetBook(){ String isbn = "8131721019"; Book myBook = mockedBookDAL.getBook(isbn); assertNotNull(myBook); assertEquals(isbn, myBook.getIsbn()); assertEquals("Compilers Principles", myBook.getTitle()); assertEquals(4, myBook.getAuthors().size()); assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication()); assertEquals((Integer)2008, myBook.getYearOfPublication()); assertEquals((Integer)1009, myBook.getNumberOfPages()); } @Test public void testAddBook(){ String isbn = mockedBookDAL.addBook(book1); assertNotNull(isbn); assertEquals(book1.getIsbn(), isbn); } @Test public void testUpdateBook(){ String isbn = mockedBookDAL.updateBook(book1); assertNotNull(isbn); assertEquals(book1.getIsbn(), isbn); } } One can run the test by using maven command: mvn test. The output is: ------------------------------------------------------- T E S T S ------------------------------------------------------- Running info.sanaulla.AppTest Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.029 sec Running info.sanaulla.dal.BookDALTest Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.209 sec Results : Tests run: 5, Failures: 0, Errors: 0, Skipped: 0 So we have been able to test the DAL class without actually configuring the data source by using mocks.

The WebLogic Server 12c has very nice support for Maven now. The doc for this is kinda hidden though, so here is a direct link http://docs.oracle.com/middleware/1212/core/MAVEN To summarize the doc, Oracle did not provide a public Maven repository manager hosting for their server artifacts. However they do now provide a tool for you to create and populate your own. You can setup either your local repository (if you are working mostly on your own in a single computer), or you may deploy them into your own internal Maven repository manager such as Archiva or Nexus. Here I would show how the local repository is done. First step is use a maven plugin provided by WLS to populate the repository. I am using a MacOSX for this demo and my WLS is installed in $HOME/apps/wls12120. If you are on Windows, you may install it under C:/apps/wls12120. $ cd $HOME/apps/wls12120/oracle_common/plugins/maven/com/oracle/maven/oracle-maven-sync/12.1.2/ $ mvn install:install-file -DpomFile=oracle-maven-sync.12.1.2.pom -Dfile=oracle-maven-sync.12.1.2.jar $ mvn com.oracle.maven:oracle-maven-sync:push -Doracle-maven-sync.oracleHome=$HOME/apps/wls12120 -Doracle-maven-sync.testingOnly=false The artifacts are placed under your local $HOME/.m2/repository/com/oracle. Now you may use Maven to build Java EE application with these WebLogic artifact as dependencies. Not only these are available, the push also populated some additional maven plugins that helps development more easy. For example, you can generate a template project using their archetype plugin. $ cd $HOME $ mvn archetype:generate \ -DarchetypeGroupId=com.oracle.weblogic.archetype \ -DarchetypeArtifactId=basic-webapp \ -DarchetypeVersion=12.1.2-0-0 \ -DgroupId=org.mycompany \ -DartifactId=my-basic-webapp-project \ -Dversion=1.0-SNAPSHOT Type 'Y' to confirm to finish. Notice that pom.xml it generated; it is using the "javax:javaee-web-api:6.0:provided" dependency. This is working because we setup the repository earlier. Now you may build it. $ cd my-basic-webapp-project $ mvn package After this build you should have the war file under the target directory.You may manually copy and deploy this into your WebLogic server domain. Or you may continue to configure the maven pom to do this all with maven. Here is how I do it. Edit the my-basic-webapp-project/pom.xml file and replace the weblogic-maven-plugin plugin like this: com.oracle.weblogic weblogic-maven-plugin 12.1.2-0-0 ${oracleMiddlewareHome} ${oracleServerUrl} ${oracleUsername} ${oraclePassword} ${project.build.directory}/${project.build.finalName}.${project.packaging} ${oracleServerName} true ${project.build.finalName} With this change, you may deploy the webapp into WebLogic server (well, assuming you already started your "mydomain" with "myserver" server running locally. See my previous blog for instructions) $ cd my-basic-webapp-project $ mvn weblogic:deploy -DoracleMiddlewareHome=$HOME/apps/wls12120 -DoracleServerName=myserver -DoracleUsername=admin -DoraclePassword=admin123 After the "BUILD SUCCESS" message, you may visit the http://localhost:7001/basicWebapp URL. Revisit the WLS doc again and you will find that they also provide other project templates (Maven calls these archetypes) for building EJB, MDB, or WebService projects. These should help you get your EE projects started quickly.

This story goes back at least a decade, when I was first approached by a PHB with a question “How big servers are we going to need to buy for our production deployment”. The new and shiny system we have been building was nine months from production rollout and apparently the company had promised to deliver the whole solution, including hardware. Oh boy, was I in trouble. With just a few years of experience down my belt, I could have pretty much just tossed a dice. Even though I am sure my complete lack of confidence was clearly visible, I still had to come up with the answer. Four hours of googling later I recall sitting there with the same question still hovering in front of my bedazzled face: “How to estimate the need for computing power?” In this post I start to open up the subject by giving you rough guidelines on how to estimate memory requirements for your brand new Java application. For the impatient ones – the answer will be to start with the memory equal to approximately 5 x [amount of memory consumed by Live Data] and start the fine-tuning from there. For the ones more curious about the logic behind, stay with me and I will walk you through the reasoning. First and foremost, I can only recommend to avoid answering a question phrased like this without detailed information being available. Your answer has to be based upon the performance requirements, so do not even start without clarifying those first. And I do not mean way-too-ambiguous “The system needs to support 700 concurrent users”, but a lot more specific ones about latency and throughput, taking into account the amount of data, usage patterns. One should also not forget about the budget also – we all can all dream about sub-millisecond latencies, but those without HFT banking backbone budgets – unfortunately it will only remain a dream. For now, lets assume you have those requirements in place. Next stop would be to create the load test scripts emulating user behaviour. If you are now able to launch those scripts concurrently you have built a foundation to the answer. As you might also have guessed, the next step involves our usual advice of measuring not guessing. But with a caveat. Live Data Size Namely, our quest for the optimal memory configuration requires capturing the Live Data Size. Having captured this, we have the baseline configuration in place for the fine-tuning. How does one define live data size? Charlie Hunt and Binu John in their “Java Performance” book have given it the following definition: Live data size is the heap size consumed by the set of long-lived objects required to run the application in its steady state. Equipped with the definition, we are ready to run your load tests against the application with the GC logging turned on (-XX:+PrintGCTimeStamps -Xloggc:/tmp/gc.log -XX:+PrintGCDetails) and visualize the logs (with the help of gcviewer for example) to determine the moment when the application has reached to the steady state. What you are after looks similar to the following: We can see the GC doing its job both with minor and Full GC runs in a familiar double-saw-toothed graphic. This particular application seems to have achieved a steady state already after the first full GC run on 21st second. In most cases however, it takes 10-20 Full GC runs to spot the change in trends. After four full GC runs we can estimate that the Live Data Size is equal to approximately 100MB. The aforementioned Java Performance book is now indicating that there is a strong correlation between the Live Data Size and the optimal memory configuration parameters in a typical Java EE application. The evidence from the field is also backing up their recommendations: Set the maximum heap size to 3-4 x [Live Data Size] So, for our application at hand, we should set the -Xmx to be in between 300m and 400m for the initial performance tests and take it from there. We have mixed feelings about other recommendations given in the book, recommending to set the maximum permanent generation size to 1.2-1.5 x [Live Data Size of the Permanent Generation] and the -XX:NewRatio being set to 1-1.5 x of the [Live Data Size]. We are currently gathering more data to determine whether the positive correlation exists, but until then I recommend to base your survival and eden configuration decisions on monitoring your allocation rate instead. Why should one bother you might now ask. Indeed, two reasons for not caring immediately surface: 8G memory chip is in sub $100 territory at the time of writing this article Virtualization, especially when using large providers such as Amazon AWS make adjusting the capacity easy Both of the reasons are partially valid and have definitely reduced the need for provisioning to be precise. But both of them are still putting you in the danger zone When tossing in huge amounts of memory “just in case” you are most likely going to significantly affect the latency – going into heaps above 8G it is darn easy to introduce Full GC pauses spanning over tens of seconds. When over-provisioning with the mindset of “lets tune it later”, the “later” part has a tendency of never arriving. I have faced numerous applications running on vastly over provisioned environments just because of this. For example the aforementioned application I discovered running on Amazon EC2 m1.xlarge instance was costing the company $4,200 per instance / year. Converting it to m1.small reduced the bill to just $520 for the instance. 8-fold cost reduction will be visible from your operations budget if your deployments are large, trust me on this. Summary Unfortunately I still see way too many decisions made exactly like I was forced to do a decade ago. This leads to the under- and over planning of capacity, both of which can be equally poor choices, especially if you cannot enjoy the benefits of virtualization. I got lucky with mine, but you might not get away with your guestimate, so I can only recommend to actually plan ahead using the simple framework described in this post. If you enjoyed the content, I can only recommend to follow our performance tuning advice in Twitter.

This article deals with different approaches to load multiple versions of the same class. The problem: Many times during the development you will need to work with different libraries versions which not always backward compatible or from some reason you need to support multiple versions of the same library. Using standard Java classloaders will not solve this issue since they all use "loadClass" method to load a specific class only once. After that "loadClass" will return the reference of the existing Class instance. The solution: Using another classloader to load the library (or multiple classloaders). There are several approaches available to achieve that: Use a URLClassLoader: This class loader will allow you to load your jars via URLs, or specify a directory for your classes location. Here is an example: URLClassLoader clsLoader = URLClassLoader.newInstance(new URL[] {new URL("file:/C://Test/test.jar")}); Class cls = clsLoader.loadClass("test.Main"); Method method = cls.getMethod("main", String[].class); String[]params = new String[2]; method.invoke(null, (Object) params); 2. Write your own custom class loader. Since Java class loaders (including URLClassLoader) first ask to load classes from their parent class loader, you can encounter a situation where you will need your custom classloader to load the classes from your specified location first. In this case here is a sample of a custom class loader which do exactly that: import java.net.URL; import java.net.URLClassLoader; import java.util.List; public class CustomClassLoader extends ClassLoader { private ChildClassLoader childClassLoader; public CustomClassLoader(List classpath) { super(Thread.currentThread().getContextClassLoader()); URL[] urls = classpath.toArray(new URL[classpath.size()]); childClassLoader = new ChildClassLoader( urls, new DetectClass(this.getParent()) ); } @Override protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException { try { return childClassLoader.findClass(name); } catch( ClassNotFoundException e ) { return super.loadClass(name, resolve); } } private static class ChildClassLoader extends URLClassLoader { private DetectClass realParent; public ChildClassLoader( URL[] urls, DetectClass realParent ) { super(urls, null); this.realParent = realParent; } @Override public Class findClass(String name) throws ClassNotFoundException { try { Class loaded = super.findLoadedClass(name); if( loaded != null ) return loaded; return super.findClass(name); } catch( ClassNotFoundException e ) { return realParent.loadClass(name); } } } private static class DetectClass extends ClassLoader { public DetectClass(ClassLoader parent) { super(parent); } @Override public Class findClass(String name) throws ClassNotFoundException { return super.findClass(name); } } }

Java is a minimalist language with deliberately less features than other languages, never the less it has edge cases which strange effects, and even some common cases with surprising effects to trip up the unwary. If you are used to reading another language you can easily read Java the wrong way leaving to confusion. Variables are only references or primitives That's right, variables are not Objects. This means when you see the following, s is not an object, it is not a String, it is a reference to a String String s = "Hello"; This answers many areas of confusion such as; Q: If String is immutable how can I change it. e g. s += "!"; A: You can't in normal Java, you can only change a reference to a String. == compares references, not their contents. To add to the confusion, using == some times works. If you have two immutable values which are the same, the JVM can try to make the references the same too. e.g. String s1 = "Hi", s2 = "Hi"; Integer a = 12, b = 12; In both these case, an object pool is used so the references end up being the same. s1 == s2 and a == b are both true as the JVM has made the references to the same object. However, vary the code a little so the JVM doesn't pool the objects, and == returns false, perhaps unexpectedly. In this case you need to use equals. String s3 = new String(s1); Integer c = -222, d = -222; s1 == s2 // is true s1 == s3 // is false s1.equals(s3) // is true a == b // is true c == d // is false (different objects were created) c.equals(d) // is true For Integer, the object pool starts at -128 up to at least 127 (possibly higher) Java passes references by value All variables are passed by value, even references. This means when you have a variable which is a reference to an object, this reference is copied, but not the object. e.g. public static void addAWord(StringBuilder sb) { sb.append(" word"); sb = null; } StringBuilder sb = new StringBuilder("first "); addWord(sb); addWord(sb); System.out.println(sb); // prints "first word word" The object referenced can be changed, but changes to the copied reference have no effect on the caller. In most JVMs, the Object.hashCode() doesn't have anything to do with memory location A hashCode() has to remain constant. Without this fact hash collections like HashSet or ConcurrentHashMap wouldn't work. However, the object can be anywhere in memory and can change location without your program being aware this has happened. Using the location for a hashCode wouldn't work (unless you have a JVM where objects are not moved) For OpenJDK and the HotSpot JVM, the hashCode() generated on demand and stored in the object's header. Using Unsafe you can see whether the hashCode() has been set and even change it by over Object.toString() does something surprising rather than useful The default behaviour of toString() is to print an internal name for a class and a hashCode(). As mentioned the hashCode is not the memory location, even though it is printed in hexi-decimal. Also the class name, especially for arrays is confusing. For example; a String[] is printed as [Ljava.lang.String; The [ signifies that it is an array, the L signifies it is a "language" created class, not a primitive like byte which BTW has a code of B. and the ;signifies the end of the class. For example say you have an array like String[] words = { "Hello", "World" }; System.out.println(words); print something like [Ljava.lang.String;@45ee12a7 Unfortunately you have to know that the class is an object array, e.g. if you have justObject words, you have a problem and you have to know to call Arrays.toString(words) instead. This break encapsulation in a rather bad way and a common source of confusion on StackOverflow. I have asked different developers at Oracle about this and the impression I got is that it's too hard to fix it now. :(

This article presents the usage of sripted data set in the eclipse's BIRT.

Using Apache Commons Configuration to configure long-running applications.

The best code coverage metric for Scala is statement coverage. Simple as that. It suits the typical programming style in Scala best. Scala is a chameleon and it can look like anything you wish, but very often more statements are written on a single line and conditional “if” statements are used rarely. In other words, line coverage and branch coverage metrics are not helpful. Java tools Scala runs on JVM and therefore many existing tools for Java can be used for Scala as well. But for code coverage it’s a mistake to do so. One wrong option is to use tools that measure coverage looking at bytecode like JaCoCo. Even though it gives you a coverage rate number, JaCoCo knows nothing about Scala and therefore it doesn’t tell you which piece of code you forgot to cover. Another misfortune are tools that natively support line and branch coverage metrics only. Cobertura is a standard in Java world and XML coverage report that it generates is supported by many tools. Some Scala code coverage tools decided to use Cobertura XML report format because of its popularity. Sadly, it doesn’t support statement coverage. Statement coverage Why? Because a typical Scala statement looks like this (a single line of code): def f(l: List[Int]) = l.filter(_ > 0).filter(_ < 42).takeWhile(_ != 3).foreach(println(_)) Neither line nor branch coverage works here. When would you consider this single line as being covered by a test? If at least one statement of that line has been called? Maybe. Or all of them? Also maybe. Where is a branch? Yes, there are statements that are executed conditionally, but the decision logic is hidden in internal implementation of List. Branch coverage tools are helpless, because they don't see this kind of conditional execution. What we need to know instead is whether individual statements like _ > 0, _ < 42 or println(_) have beed executed by an automated test. This is the statement coverage. Scoverage to the rescue! Luckily there is a tool named Scoverage. It is a plugin for Scala compiler. There is also a plugin for SBT. It does exactly what we need. It generates HTML report and also own XML report containing detailed information about covered statements. Scoverage plugin for SonarQube Recently I have implemented a plugin for Sonar 4 so that statement coverage measurement can become an integral part of your team's continuous integration process and a required quality standard. It allows you to review overall project statement coverage as well as dig deeper into sub-modules, directories and source code files to see uncovered statements. Project dashboard with Scoverage plugin: Multi-module project overview: Columns with statement coverage, total number of statements and number of covered statements: Source code markup with covered and uncovered lines:

what can one create during the new year and christmas holidays? as it turned down – quite enough. even if you have two kids and a bunch of family members whom you want to visit. the only thing you cannot accomplish in time is to finish an article for dzone. it takes a lot of time, nearly the entire january. by the 5th of january i had a laptop and a couple of days to spend on some development. having estimated what i can do here, i decided to create a mobile app that would work faster than the original. for this, i needed to find communicative creators of a popular app. hence, i found a “ spender ” app in the app store. it is a simple app for tracking your budget. with it, you can estimate how effectively you spend your money in the end of each month. by the 5th of january, this app was in top-10 in the russian app store. i also found their dev-story on iphones.ru. in their dev-story, the developers wrote that after completing their previous project, they had three-four free days. so, they decided to create a new app during this free time. their product manager and programmers helped them with positioning the app and its key features. this encouraged me and i began to think how to create nearly the same app in 2 days . note: the original app was updated in the middle of january, and now it looks a little different from my app. anyway, you can find its screenshots in the dev-story. i already had the experience of mobile app development using c# and cocoa. since this was my personal free time, i wanted to use it with maximum effectiveness. even if i didn’t succeed, i was eager to learn a new framework or programming language. i was working for devexpress from 2006 till2011 and have been reading their announces since i left the company. so, i knew that they created a mobile js-framework based on cordova/phonegap. they made it after i left the company, so i was curious to try it. the gartner research company reports that by august, 2013 most of the enterprise mobile software was created using phonegap or phonegap-based products (like kony ). from my consumer experience, it's far from true. maybe i was wrong? i'm not so good at html and javascript. i can create mark-up with stackoverflow.com and i can write simple selectors with jquery. i can also find the required information in their documentation. in other words, html+js was a gap in my knowledge and i was ready to fill it or gain some experience. thus, i planned to create a cross-platform application that could become an advantage over the original ios-only spender app. moreover, i wanted to spend my time in the most effective way. on the one hand, i had a potentially effective js framework, on the other – a lack of js experience. i hoped that the js framework advantages could balance my poor experience. since i like to use a vcs during development, i'll try to recover my progress. you can download complete apps here: ios , android i'm not sure i can provide public access to my repo, because it contains images i bought from fotolia and third-party libraries, each with a difference license. i'm not a lawyer, so i’d prefer not to take the risk. the most curious of you can take a look into the app bundle itself. js wasn't minified. place: tula, russia, date: january, 5, 2014 +20 minutes spent on installing node.js and cordova cli +10 minutes downloaded a template app from cordova. added a template from phonejs. created a git-repo, registered it in webstorm. added a new record to the httpd.conf in order to have an ability to debug my future app in the browser. +38 minutes changed the app namespace to "io.nikitin.thriftbox". added navigation. phonejs is an mvc-framework. each app screen is represented as a collection of html markup (views) and fabric function (viewmodel). here is how it looks at its simplest // view content and thriftbox.home = function (params) { // request parameters taken from uri return {}; // viewmodel instance }; then view and view model are bound via knockout-bindings . to be in time, i create only two screens: expense input and monthly expense report. +4 hours 20 minutes here i got stuck for the first time. i couldn't create a markup of digit buttons. the original app had a huge keyboard that looked like a calculator or dialer. i found out that it was not that easy to create such a keyboard, even using a table tag. in the iphone retina screen, 1px borders between buttons changed their colors after clicking on the buttons. on my iphone, the difference in colors was very noticeable. i had to invent how to tackle this. i tried to implement buttons using div s. but i couldn't achieve a border width of 1 px and make all buttons look equal in different screens. three hours later i gave up the idea of using divs and moved forward. +28 minutes removing a clicked button indicator on ios. ios displays a gray indicator around tapped links and objects with the onclick event handler. since i had my own indicator of a tapped object (the tapped button became darker), i didn't need the default indicator. i solved this problem using the dxaction event: was: 1 became: 1 this event is an extended variation of a "click" event: its handler supports uri navigation between views and correctly works in the scrollable area. +14 minutes the buttonpress event handler shown in the previous example now validates numbers from user input. var number = ko.observable(null); var isvalidnumber = ko.computed(function() { return number() && parsefloat(number()) > 0; }); ...... function buttonpress(button) { if (button) { if (number()) number(number() + button); else number(button); } else if (number()) number(number().substr(0, number().length - 1)); } var viewmodel = { number: number, isvalidnumber: isvalidnumber, viewshowing: viewshowing, buttonpress: buttonpress }; ..... +8 minutes added a fastclick.js , which removes a delay between tapping the screen and raising the 'click' event on phones. the mobile browser delays the raising of the click event by default to be sure the end-user will not perform a double tap. for the end-user, this looks as if the app is sluggish. you click buttons much faster than an app responds. fastclick.js handles the touchstart event and then creates all the click event process logic. btw, adding this library was a mistake; later i'll tell why. +4 minutes added a limitation to the length of user input numbers. corrected the font size for a better look-and-feel. +58 minutes added a choice of an expense category. added a scrollable pane with available categories below the input field. video . it took less time than it could be. in the phonejs component collection, i found dxtileview . it provides a kinetic scrolling with the required appearance out-of-the-box. it's not easy to implement kinetic scrolling by yourself and thus it’s great that this scrolling is enabled for ios only - android doesn't have it. it was 7:40 pm, so, i decided to continue the next day. place: tula, russia, date: january, 5, 2014 +3 hours 9 minutes storing data on a local storage. phonejs contains classes for working with data: selection, filtering, sorting, and grouping. there are several approaches to store data: odata and localstorage. i didn't want to implement a server side for a free app, and decided to use localstorage. later i found out that this was not an ideal decision. for example, when updating to ios 5.1 user data is erased , other people complained that localstorage is cleared regularly or even when shutting the device down. i didn't want to risk, so i used file api of phonegap. documentation says that this api is based on w3c file api. in fact, this means that this api differs in safari for mac os, chrome for mac os, cordova for ios and cordova for android. file api implementation is different for ios and android . e.g. android implementation doesn't contain the 'blob' class and 'window.permanent' constant. ii however implements the 'localfilesystem' and 'localfilesystem.persistent' classes. the laptop browser provides additional api for requesting an additional storage space, which mobile browsers don't provide. the available documentation for this api adds more problems. i found several articles searching by "html5 file api". and, i couldn't find an article that would cover all my questions. finally i created a new class for working with fileapi. this class supports cordova 3.3 on ios, android, and chrome 32 for mac os and windows 8. you can find it here: https://github.com/chebum/filestorage-for-phone.js/blob/master/filestorage.js you can use it as follows: // in this example i create data/records file in the documents folder of the app fs.initfileapi(1000000, true) .then(function () { var records = new fs.filearraystore({ key: "id", filename: "records" }); return records.insert({ customer: "peter" }) }) .then(function () { alert("record saved!"); }); // or use low-level api: fs.initfileapi(100000, true) .then(function() { return fs.writefile("file1", "file content") }) .then(function() { alert("file saved!"); }); +33 minutes saving the added records to the storage. category list is stored in arraystore , to simplify the selection operations. +26 minutes creating layout for the app's views. phonejs provides several layouts that are the placeholders for the views. my app's start page didn't fit into any of the available layout, so i have chosen the emptylayout. but, it doesn't provide animation effects when navigating through views. i copied the emptylayout code and added an attribute that had animation effects. +1 h. 51 min. template's about screen was redesigned to a report screen, empty by that moment. created a viewmodel that selects data for a current month. added localization date formatting for the screen caption. +59 minutes added the display of expenses grouped by categories for a current month. +28 minutes added the selection of months for which the report should be generated. end-users can tap the screen header to select the required month. +1 h. 20 min. added cordova-plugin statusbar that didn't work outof-the-box. i found that the reference to cordova.js was commented in the phonejs app template: as a result, the native part of my app didn't work. +39 minutes in the report screen, the upper part was changed to dxtoolbar . +22 minutes i discoveredwhy the dxbutton click event handler didn't work. removing the fastclick.js solved my problem, but caused a delay between tapping and event raising. i've changed the dxaction event subscription to 'touchstart'. +25 minutes formatting output strings when generating a report. at night i dreamed of crappy buttons in the application’s main screen. places: tula, vnukovo airport, date: january, 7-8, 2014 i had an early flight to budapest from vnukovo, and because i had no time in the afternoon, i gradually completed at the airport at night. as you know, it’s not very comfortable to sleep or sit in a café chair for a long time, but it turned out that programming was ok. +2 h. 5 min. in the morning, i decided to split the buttons in order to remove borders between them. i took the ios dialer keyboard as a sample. i created three keyboards. the button size changes depending on screen resolution: for 3.5'', 4'' and 5'' phones. each table cell contained a div with configured alignment. because of the lack of an incomplete vertical text alignment in html, the final css style for buttons ended to be quite complex: .home-view .buttons td div { color: #4a5360; border: 1px solid #4a5360; text-align: center; position: absolute; left: 50%; /* small buttons - default */ font-size: 26px; padding: 13px 0 13px 0; width: 52px; line-height: 26px; border-radius: 26px; margin-left: -27px; margin-top: -27px; } +1 h. 50 minutes i bought several vector icon sets on fotolia. i cut the required icons and converted them to png. it took me quite a long time, maybe, because it was 1.30 am :) +1 hour 10 minutes added a splash-screen for the app. +36 minutes created three sizes for the app icon. localized the app name for ios. +20 minutes hiding the splash screen after the app is completely loaded. +2 hours fixing multiple bugs. +2 hours creating screenshots for play store +30 minutes creating screenshots for app store +30 minutes writing an app description for two app stores. +1 h. 30 minutes submitting my app to the app store. here i faced with an issue with the app certification. my accountancy let's summarize the time i spent and divide it into categories. development: 21 hours 37 minutes graphics and texts: 8 hours 26 minutes totally: 30 hours 3 minutes as a result, i got a minimum-feature working app, though it is not as cool as the latest version of "spender". i couldn't create splitting expenses by days and income input. my app's ui could be more elegant as well. after analyzing the original 'spender' developer work, i got the following. they say that they involved four developers for three-four days. it is about 96-128 man-hours. i spent only 30 man-hours and got an app for three mobile platforms. ios and android versions are already in stores. the version for windows phone 8 requires a ui redesign. i can be proud of myself :). you can download complete apps here: ios , android

Lambda expressions are by far the most discussed and promoted feature of Java 8. While I agree that Lambdas are a large improvement I think that some other Java 8 feature go a bit short because of the Lambda hype. In this post I want to show a number of examples from another nice Java 8 feature: Type Annotations. Type Annotations are annotations that can be placed anywhere you use a type. This includes the new operator, type casts, implements clauses and throws clauses. Type Annotations allow improved analysis of Java code and can ensure even stronger type checking. In source code this means we get two new ElementTypes for annotations: @Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER}) public @interface Test { } The enum value TYPE_PARAMETER allows an annotation to be applied at type variables (e.g. MyClass). Annotations with target TYPE_USE can be applied at any type use. Please note that the annotations from the following examples will not work out of the box when Java 8 is released. Java 8 only provides the ability to define these types of annotations. It is then up to framework and tool developers to actually make use of it. So this is a collection of annotations frameworks could give us in the future. Most of the examples are taken from the Type Annotations specification and various Java 8 presentations. Simple type definitions with type annotations look like this: @NotNull String str1 = ... @Email String str2 = ... @NotNull @NotBlank String str3 = ... Type annotations can also be applied to nested types Map.@NonNull Entry = ... Constructors with type annotations: new @Interned MyObject() new @NonEmpty @Readonly List(myNonEmptyStringSet) They work with nested (non static) class constructors too: myObject.new @Readonly NestedClass() Type casts: myString = (@NonNull String) myObject; query = (@Untainted String) str; Inheritance: class UnmodifiableList implements @Readonly List { ... } We can use type Annotations with generic type arguments: List<@Email String> emails = ... List<@ReadOnly @Localized Message> messages = ... Graph<@Directional Node> directedGraph = ... Of course we can nest them: Map<@NonNull String, @NonEmpty List<@Readonly Document>> documents; Or apply them to intersection Types: public & @Localized MessageSource> void foo(...) { ... } Including parameter bounds and wildcard bounds: class Folder { ... } Collection c = ... List<@Immutable ? extends Comparable> unchangeable = ... Generic method invocation with type annotations looks like this: myObject.<@NotBlank String>myMethod(...); For generic constructors, the annotation follows the explicit type arguments: 1 new @Interned MyObject() Throwing exceptions: void monitorTemperature() throws @Critical TemperatureException { ... } void authenticate() throws @Fatal @Logged AccessDeniedException { ... } Type annotations in instanceof statements: boolean isNonNull = myString instanceof @NonNull String; boolean isNonBlankEmail = myString instanceof @NotBlank @Email String; And finally Java 8 method and constructor references: @Vernal Date::getDay List<@English String>::size Arrays::<@NonNegative Integer>sort Conclusion Type annotations are an interesting addition to the Java type system. They can be applied to any use of a type and enable a more detailed code analysis. If you want to use Type annotations right now you should have a look at the Checker Framework.

The current release of Oracle WebLogic (12.1.2) added support to HTML5 WebSocket (RFC-6455) providing the bi-directional communication over a single TCP connection between clients and servers. Unlike the HTTP communication model, client and server can send and receive data independently from each other. The use of WebSocket is becoming very popular for highly interactive web applications that depend on time critical data delivery, requirements for true bi-directional data flow and higher throughput. To initiate the WebSocket connection, the client sends a handshake request to the server. The connection is established if the handshake request passes validation, and the server accepts the request. When a WebSocket connection is established, a browser client can send data to a WebLogic Server instance while simultaneously receiving data from that server instance. The WebLogic server implementation has the following components: The WebSocket protocol implementation that handles connection upgrades and establishes and manages connections as well as exchanges with the client. The WebLogic server fully implements the WebSocket protocol using its existing threading and networking infrastructure. The WebLogic WebSocket Java API, through the weblogic.websocket package, allows you to create WebSocket-based server side applications handling client connections, WebSocket messages, providing context information for a particular WebSocket connection and managing the request/response handshake. For additional information about the WebLogic WebSocket Java API interfaces and classes, visit the following resource: http://docs.oracle.com/middleware/1212/wls/WLPRG/websockets.htm#BABJEFFD To declare a WebSocket endpoint you use the @WebSocket annotation that allow you to mark a class as a WebSocket listener that's ready to be exposed and handle events. The annotated class must implement the WebSocketListener interface or extend from the WebSocketAdapter class. When you deploy the WebSocket-based application on WebLogic, you basically follow the same approach using the standard Java EE Web Application archives (WARs), either as standalone or WAR module. Either way, the WebLogic Application Server detects the @WebSocket annotation on the class and automatically establishes it as a WebSocket endpoint. Here is a simple application that creates a WebSocket endpoint at the /echo/ location path, receives messages from the client and sends the same message back to the client. import weblogic.websocket.WebSocketAdapter; import weblogic.websocket.WebSocketConnection; import weblogic.websocket.annotation.WebSocket; @WebSocket(pathPatterns={"/echo/*"}) public class Echo extends WebSocketAdapter{ @Override public void onMessage(WebSocketConnection connection, String msg){ try{ connection.send(msg); }catch(IOException ioe){ //Handle error condition } } } n the client side, you typically use the WebSocket JavaScript API that most of the web browsers already support. There are many samples out there that you can use to test the implementation above. One quick way of doing that is to navigate to http://www.websocket.org/echo.html and then point the location field to your WebLogic server. If you follow the sample available on https://github.com/mjabali/HelloWorld_WebSocket then you'll end up with something like ws://localhost:7001/HelloWorld_WebSocket/echo/ for the WebSocket server application. The sample client provided will be available at http://localhost:7001/HelloWorld_WebSocket/index.html after the WebLogic deployment. See the README.md file on GitHub for additional instructions. Have fun!

If you are a programmer and have to deal with cryptography issues, you've surely heard about keywords such as encryption, decryption and key management. The last key word, key management, is defined as a group of operations such as generating, exchanging, storing and protecting security artifacts (i.e. keys and certificates). Security artifacts are essential parts of any cryptography operations. Without effective management of such valuable resources, the system can be easily compromised by attackers. Java supports key management by introducing two utilities; Java Keys Store or JKS as short and Java Keytool Utility. Java Key Store is a handy and safe storage to store keys and certificates. Java key store API describes methods and properties of Java keystore class which makes it possible to work with keystore file programmatically. To manage keys and certificates, Java provides a second utility named Java Keytool Utility. Keytool utility is included and delivered with JDK (Java Development Kit) distributions. The Keytool manual introduces and describes various commands and options that are available and provides by Java Keytool utility. Key management is feasible by services that are offered by both Java keystore and Java Keytool utility together. The Key management that Java provides is covering most of programming scenarios. Unfortunately there is only one limitation. Java Keytool utility as the main key management unit does not support any means to import custom created keys to Java keystore. It only supports key generation which results in auto generated keys. This is a major shortcoming in situations where there must be key exchange between application peers. In such situations key specifications are specific to the security models which are agreed between developers. Sometimes the keys are byte streams which are not accompanied with any certificates. These streams are defined as cryptography artifacts and must be protected and saved by Java keystore. One solution to this problem is to use third party utilities such as Openssl. Openssl utility offers a mechanism which is a hack to the unavailability of key import in Java Keytool utility. The trick is to save keys in PKCS12 format using the Openssl utility, and treating the created artifact as a new keystore. Fortunately Java Keytool utility supports key store merge option. The created keystore by Openssl utility then can be merged into any Java keystore by Java Keytool utility. Unfortunately I could not succeed in following this solution. One reason could be that my key had customized specifications such as size and value, plus there was no certificate available to accompany it as well. It seemed that there was no other way to overcome such limitation. I found a solution, pretty easy and quick that helped me achieving the result I wanted without being dependent on any third party tools. One advantage of this method is the use of current options that are offered by both Keytool and Java Keystore utilities. Let’s name this method “Key Replacement”. Firstly a new key must be created, for example, a secret key. The secret key will be auto generated by the Keytool utility and will be saved under a known ALIAS inside a new key store or in an existing one. Open your command prompt and issue the following command: keytool -genseckey -alias mykey -keyalg DES -keysize 56 -storetype jceks -keystore Make sure you have set your Java runtime environment correctly. Description and details of the above command and options can be found on Keytool manual. After issuing the above command, you will be asked to provide a password for the keystore. If the keystore already exists, provide its password; otherwise enter a password to be set for the newly created keystore. If the operation was successful, you can list the keystore entries by issuing the following command: keytool -list -v -storetype JCEKS -keystore The result of list command will be a list of keystore's entries. In our case, the record we seek is something like : Keystore type: JCEKS Keystore provider: SunJCE Your keystore contains 1 entry Alias name: mykey Creation date: Sep 30, 2013 Entry type: SecretKeyEntry As you can see the newly created key is represented by the alias we have set. This key is auto generated by Java Keytool utility. We are one step closer to what we needed. We have created a key entry with the alias we want. The final step is to change the key entry value with our customized value. Remaining steps consists of, locating the target key entry inside the keystore by its alias and change its value with our own value programmatically. The following simple java program will do the job. KeyStore ks = KeyStore.getInstance("JCEKS"); char[] password = "PASSWORD TO KEYSATORE".toCharArray(); java.io.FileInputStream fis = null; try { ks.load(new FileInputStream("PATH TO KEY STORE"), password); } finally { if (fis != null) { fis.close(); } } SecretKey mySecretKey = new SecretKeySpec(Util.hex2byte("5A5A5A5A5A5A5A5A"), 0, Util.hex2byte("5A5A5A5A5A5A5A5A").length, "DES"); KeyStore.SecretKeyEntry skEntry = new KeyStore.SecretKeyEntry(mySecretKey); ks.setEntry("mykey", skEntry, new KeyStore.PasswordProtection(password)); java.io.FileOutputStream fos = null; try { fos = new java.io.FileOutputStream("PATH TO KEYSTORE"); ks.store(fos, password); } finally { if (fos != null) { fos.close(); } } This java program will: · Open the keystore. · Load the key store prior to any operation. · Build a secret key with desired specs (Custom value and Custom length). · Replace the value of target key by using the setEntry() method of keystore object by providing its alias and a new key value. · Finally close and save the keystore object. To double check the modification, use the following code to locate and display the modified key value by loading the keystore object again. try { ks.load(new FileInputStream("PATH TO KEY SOTRE"), password); } finally { if (fis != null) { fis.close(); } } Key key = ks.getKey("mykey ", password); System.out.println("-----BEGIN PRIVATE KEY-----"); System.out.println(new BASE64Encoder().encode(key.getEncoded())); System.out.println("-----END PRIVATE KEY-----"); The steps are straight forward: · Load the key store object. · Load the target key by using the getKey() method and specifying its alias. · Fetch the key value and output its value in PEM format (Base 64 encoding). Voila! That’s our key. This article shows some simple steps which can be used to import a custom created secret key to java keystore. Hope this article will be helpful in cases where the tools such as Openssl utility has no use. Sam,

I needed to diff some OPML files today and came across this project. Even through it's 10 years old, it still mostly worked and the best part is it's a source distrib... :) The XML Diff and Patch GUI Tool Amol Kher Microsoft Corporation July 2004 Applies to: the XML Diff and Patch GUI tool Summary: This article shows how to use the XmlDiff class to compare two XML files and show these differences as an HTML document in a .NET Framework 1.1 application. The article also shows how to build a WinForms application for comparing XML files. Contents Introduction An Overview of the XML Diff and Patch API XML Diff and Patch Meets Winforms Working with XML DiffGrams Other Features of the XML Diff and Patch Tool Introduction There is no good command line tool that can be used to compare two XML files and view the differences. There is an online tool called XML Diff and Patch that's available on the GotDotNet website under the XML Tools section. For those who have not, you can find it at Microsoft XML Diff and Patch 1.0 [GD: yes, this link is busted... you can download it below]. It is a very convenient tool for those who want to compare the difference between two XML files. Comparing XML files is different from comparing regular text files because one wants to compare logical differences in the XML nodes not just differences in text. For example one may want to compare XML documents and ignore white space between elements, comments or processing instructions. The XML Diff and Patch tool allows one to perform such comparisons but it is primarily available as an online web application. We cannot take this tool and use it from command line. This article focuses on developing a command-line tool by reusing code from the XML Diff and Patch installation and samples. The tool works very similar to the WinDiff utility; it presents the differences in a separate window and highlights them. The XML Diff and Patch tool contains a library that contains an XmlDiff class, which can be used to compare two XML documents. The Compare method on this class takes two files and either returns true, if the files are equal, or generates an output file called an XML diffgram containing a list of differences between the files. The XmlDiff class can be supplied an options class XmlDiffOptions that can be used to set the various options for comparing files. ... Microsoft Downloads - XML Diff & Patch GUI Tool Winforms application that can be used to compare 2 XML files. Version: 1.0 Date Published: 7/14/2004 xmldiffgui.msi, 278 KB This code sample shows how to build a Windows forms application that utilizes the XML Diff & Patch library to show the difference between 2 XML files. There's a bug somewhere in it in that it was giving me an error when trying to load the HTML into an IE window, but that's likely a path thing. In the end, it executed and diff'd the two XML files. And since we do have the source... :) Another blast from the past is that this was available on the old GotDotNet site. I miss that site... :(

At the end of last year I was playing around with running scheduled tasks to monitor a Neo4j cluster and one of the problems I ran into was that the monitoring would sometimes exit. I eventually realised that this was because a RuntimeException was being thrown inside the Runnable method and I wasn’t handling it. The following code demonstrates the problem: import java.util.ArrayList; import java.util.List; import java.util.concurrent.*; public class RunnableBlog { public static void main(String[] args) throws ExecutionException, InterruptedException { ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor(); executor.scheduleAtFixedRate(new Runnable() { @Override public void run() { System.out.println(Thread.currentThread().getName() + " -> " + System.currentTimeMillis()); throw new RuntimeException("game over"); } }, 0, 1000, TimeUnit.MILLISECONDS).get(); System.out.println("exit"); executor.shutdown(); } } If we run that code we’ll see the RuntimeException but the executor won’t exit because the thread died without informing it: Exception in thread "main" pool-1-thread-1 -> 1391212558074 java.util.concurrent.ExecutionException: java.lang.RuntimeException: game over at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252) at java.util.concurrent.FutureTask.get(FutureTask.java:111) at RunnableBlog.main(RunnableBlog.java:11) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120) Caused by: java.lang.RuntimeException: game over at RunnableBlog$1.run(RunnableBlog.java:16) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) At the time I ended up adding a try catch block and printing the exception like so: public class RunnableBlog { public static void main(String[] args) throws ExecutionException, InterruptedException { ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor(); executor.scheduleAtFixedRate(new Runnable() { @Override public void run() { try { System.out.println(Thread.currentThread().getName() + " -> " + System.currentTimeMillis()); throw new RuntimeException("game over"); } catch (RuntimeException e) { e.printStackTrace(); } } }, 0, 1000, TimeUnit.MILLISECONDS).get(); System.out.println("exit"); executor.shutdown(); } } This allows the exception to be recognised and as far as I can tell means that the thread executing the Runnable doesn’t die. java.lang.RuntimeException: game over pool-1-thread-1 -> 1391212651955 at RunnableBlog$1.run(RunnableBlog.java:16) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) pool-1-thread-1 -> 1391212652956 java.lang.RuntimeException: game over at RunnableBlog$1.run(RunnableBlog.java:16) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) pool-1-thread-1 -> 1391212653955 java.lang.RuntimeException: game over at RunnableBlog$1.run(RunnableBlog.java:16) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) This worked well and allowed me to keep monitoring the cluster. However, I recently started reading ‘Java Concurrency in Practice‘ (only 6 years after I bought it!) and realised that this might not be the proper way of handling the RuntimeException. public class RunnableBlog { public static void main(String[] args) throws ExecutionException, InterruptedException { ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor(); executor.scheduleAtFixedRate(new Runnable() { @Override public void run() { try { System.out.println(Thread.currentThread().getName() + " -> " + System.currentTimeMillis()); throw new RuntimeException("game over"); } catch (RuntimeException e) { Thread t = Thread.currentThread(); t.getUncaughtExceptionHandler().uncaughtException(t, e); } } }, 0, 1000, TimeUnit.MILLISECONDS).get(); System.out.println("exit"); executor.shutdown(); } } I don’t see much difference between the two approaches so it’d be great if someone could explain to me why this approach is better than my previous one of catching the exception and printing the stack trace.

Learn how to convert XML objects to Java, and vice versa.

Within this blog post I describe how you can use AspectJ to automatically translate one type of exception to another. The problem Sometimes we are in situations where we have to convert an exception (often thrown by a third-party library) to another type of exception. Assume you are using a persistence framework like hibernate and you do not want to leak hibernate specific exceptions out of a certain application layer. Maybe you are using more than one persistence technology and you want to wrap technology specific exceptions into a common base exception. In such situations, one can end with code like this: public class MyRepository { public Object getSomeData() { try { // assume hibernate is used to access some data } catch(HibernateException e) { // wrap hibernate specific exception into a general DataAccessException throw new DataAccessException(e); } } } Of course this becomes ugly if you have to do this every time you access a certain framework. The AspectJ way AspectJ is an aspect oriented programming (AOP) extension for Java. With AspectJ we can define Cross-cutting concerns that take care of the exception translation process for us. To get started we first have to add the AspectJ dependency to our project: org.aspectj aspectjrt 1.7.4 Next we have to set up ajc, the compiler and bytecode weaver for AspectJ. This step depends on the developing environment you are using, so I will not go into details here. Eclipse users should have a look at theAspectJ Development Tools (AJDT) for Eclipse. IntelliJ IDEA users should make sure the AspectJ plugin is enabled. There is also an AspectJ Maven plugin available (check this pom.xml for an example configuration). Now let's define our aspect using AspectJ annotations: @Aspect public class ExceptionTranslationAspect { @Around("execution(* com.mscharhag.exceptiontranslation.repository..*(..))") public Object translateToDataAccessException(ProceedingJoinPoint pjp) throws Throwable { try { return pjp.proceed(); } catch (HibernateException e) { throw new DataAccessException(e); } } } Using the @Aspect annotation we can declare a new aspect. Within this aspect we use the @Aroundannotation to define an advice that is always executed if the passed pointcut is matched. Here, the pointcut execution(* com.mscharhag.exceptiontranslation.repository..*(..)) tells AspectJ to call translateToDataAccessException() every time a method of a class inside thecom.mscharhag.exceptiontranslation.repository package is executed. Within translateToDataAccessException() we can use the passed ProceedingJoinPoint object to proceed the method execution we intercepted. In this example we just add a try/catch block around the method execution. Using the ProceedingJoinPoint instance we could also do more interesting things like analyzing the method signature using pjp.getSignature() or accessing method parameters withpjp.getArgs(). We can now remove the try/catch block from the example repository implementation shown above and use a simple test to verify our aspect is working: public class MyRepositoryTest { private MyRepository repository = new MyRepository(); @Test(expected = DataAccessException.class) public void testExceptionTranslation() { this.repository.getSomeData(); } } Conclusion Using AspectJ we can easily automate the conversion of Java runtime exceptions. This simplifies our code by removing try/catch blocks that would otherwise be required for exception translation. You can find the full source of the example project on GitHub.