The current Java Persistence API (JPA) standard does not mandate JPA provider to support data type conversions through annotations, not even a with simple boolean field. For readers who are unfamiliar with JPA, what I mean is, to persist a boolean field, JPA expects the database data type to be integer, where value of "1" means true, and value of "0" means false. We simply just can't annotate the boolean field, specifying our own boolean field value, such as "True/False", "T/F", "Yes/No", "Y/N", "-1/0" and then let the JPA provider to convert those boolean field on the fly. As an example, I am expecting JPA will allow me to annotate a boolean field @boolean(trueValue="Yes", falseValue="No") private boolean enabled; For me, this is a very annoying limitation, espeically when you have to deliver applications on an existing database with hundreds of tables. After some research, I decided to create my own Java Annotation Processing Tool (APT) Compile Time Annotation, called @BooleanMagic, with a compile time Java APT preprocessing factory, which will automatically generate additional code to work around the issue. I've also made some changes on the original code: Fixed the bug of Null pointer exception, when JPA return null on the annotated field. Introduce a new properties call ifNull, which allows user to configure what to return if JPA returns null, it expect enum of org.jbpcc.util.jpa.ReturnType, which have values of ReturnType.True, ReturnType.FALSE, and ReturnType.Null,. The default value of ifNull is ReturnType.Null So here is an example, assuming we have model class defined as below: package org.jbpcc.domain.model; import javax.persistence.Entity; import javax.persistence.Id; import org.jbpcc.util.jpa.BooleanMagic; import org.jbpcc.util.jpa.BooleanMagic.ReturnType; @Entitypublic class SomeVO { @Id private Integer id; @BooleanMagic(trueValue = "Yes", falseValue = "No", columnName = "OVERDUED", ifNull = ReturnType.FALSE) private transient Boolean overdued; public Boolean isOverdued() { return overdued; } public void setOverdued(Boolean overdued) { this.overdued = overdued; } } Using Java APT with JPABooleanMagicConverter factory, the code above will be now be converted to: @Entitypublic class SomeVO { @Id private Integer id; private transient Boolean overdued; //--- Lines below are generated by JBPCC BooleanMagicConvertor PROCESSOR //--- START : @Column(name="OVERDUED") private String magicBooleanOverdued; public Boolean isOverdued() { if (this.magicBooleanOverdued == null) return false; return this.magicBooleanOverdued.equals("Yes") ? Boolean.TRUE : Boolean.FALSE; } public Boolean getOverdued() { if (this.magicBooleanOverdued == null) return false; return this.magicBooleanOverdued.equals("Yes") ? Boolean.TRUE : Boolean.FALSE; } public void setOverdued(Boolean trueFlag) { this.magicBooleanOverdued = trueFlag ? "Yes" : "No"; } //--- END //--- GENERATED BY JBPCC BooleanMagicConvertor PROCESSOR } I have put the annotation with it compile time process factory under my open source project - Java Batch Process control center, at http://code.google.com/p/jbpcc, I also posted an article at my blog detailing the usage of the annotation. I hope some readers will find the annotation and the APT preprocessing factory useful. Do share your thoughts and suggestions.
This turns a class name (like LineItem) into a nice string (like "line item") line_item = LineItem.new puts line_item.class.name.underscore.humanize.lowcase #spits out "line item"
# Array#to_ranges # Converts an array of values (which must respond to #succ) to an array of ranges. For example, # [3,4,5,1,6,9,8].to_ranges => [1,3..6,8..9] class Array def to_ranges array = self.compact.uniq.sort ranges = [] if !array.empty? # Initialize the left and right endpoints of the range left, right = self.first, nil array.each do |obj| # If the right endpoint is set and obj is not equal to right's successor # then we need to create a range. if right && obj != right.succ ranges << Range.new(left,right) left = obj end right = obj end ranges << Range.new(left,right) end ranges end end
A simple time based cache build around a map store. import java.util.Map; import java.util.WeakHashMap; /** * Simple time-based cache. */ public class SimpleCache { private long maxAge; private Map store; /** * Instanciate a cache with max age of 1 hour and a WeakHashMap as store. * @see java.util.WeakHashMap */ public SimpleCache() { this.maxAge = 1000 * 60 * 60; this.store = new WeakHashMap(); } /** * @param maxAge maximum age of an entry in milliseconds * @param store map to hold entries */ public SimpleCache(long maxAge, Map store) { this.maxAge = maxAge; this.store = store; } /** * Cache an object. * @param key unique identifier to retrieve object * @param value object to cache */ public void put(Object key, Object value) { store.put(key, new Item(value)); } /** * Fetch an object. * @param key unique identifier to retrieve object * @return an object or null in case it isn't stored or it expired */ public Object get(Object key) { Item item = getItem(key); return item == null ? null : item.payload; } /** * Fetch an object or store and return output of callback. * @param key unique identifier to retrieve object * @param block code executed when object not in cache * @return an object */ public synchronized Object get(Object key, Callback block) { Item item = getItem(key); if (item == null) { Object value = block.execute(); item = new Item(value); store.put(key, item); } return item.payload; } /** * Remove an object from cache. * @param key unique identifier to retrieve object */ public void remove(Object key) { store.remove(key); } /** * Get an item, if it expired remove it from cache and return null. * @param key unique identifier to retrieve object * @return an item or null */ private Item getItem(Object key) { Item item = (Item) store.get(key); if (item == null) { return null; } if (System.currentTimeMillis() - item.birth > maxAge) { store.remove(key); return null; } return item; } /** * Value container. */ private static class Item { long birth; Object payload; Item(Object payload) { this.birth = System.currentTimeMillis(); this.payload = payload; } } /** * A visitor interface. */ public static interface Callback { Object execute(); } } And a couple of junit tests: import java.util.HashMap; import junit.framework.TestCase; public class SimpleCacheTest extends TestCase { public void testPutGet () { SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap()); c.put("key1", "value1"); assertEquals("value1", c.get("key1")); c.put("key1", "value1.0"); assertEquals("value1.0", c.get("key1")); c.put("key2", "value2"); assertEquals("value2", c.get("key2")); assertEquals("value1.0", c.get("key1")); } public void testMaxAge () throws InterruptedException { SimpleCache c = new SimpleCache(1000, new HashMap()); c.put("key1", "value1"); assertEquals("value1", c.get("key1")); Thread.sleep(1500); assertNull(c.get("key1")); c.put("key2", "value2"); Thread.sleep(750); c.put("key3", "value3"); Thread.sleep(750); assertNull(c.get("key2")); assertNotNull(c.get("key3")); Thread.sleep(750); assertNull(c.get("key3")); } public void testRemove () { SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap()); c.remove("key"); assertNull(c.get("key")); c.put("key", "value"); assertNotNull(c.get("key")); c.remove("key"); assertNull(c.get("key")); } public void testCallBack () { SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap()); assertEquals("value1", c.get("key1", new SimpleCache.Callback() { public Object execute() { return "value1"; } })); assertEquals("value1", c.get("key1")); // again with a new callback (value) c.get("key1", new SimpleCache.Callback() { public Object execute() { return "value2"; } }); assertEquals("value1", c.get("key1")); } }
class Array def swap!(a,b) self[a], self[b] = self[b], self[a] self end end You can now do stuff like.. [1,2,3,4].swap!(2,3) # = [1,2,4,3] etc.. Many thanks to Sam Stephenson and technoweenie for their suggestions.
