Gerard Davison [Deactivated] [Suspended]

Senior Principal Member of Technical Staff at Oracle

Reading, GB

Joined Dec 1997

About

Gerard Davison is a Senior Principal Software Engineer working at Oracle in the UK on SOAP and REST tooling. Currently he is contributing in the area of WADL generation and client generation in the Jersey project and is maintaining the Abbot swing automation project. He also maintain a small holding of Hudson nodes run all those tests. He graduated from the University of Reading with a degree in Human Cybernetic and can't help looking for feedback loops.

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Articles

A lot of REST services will use cookies as part of the authentication / authorisation scheme. This is a problem because by default the old Jersey client will use the singletonCookieHandler.getDefault which is most cases will be null and if not null will not likely work in a multithreaded server environment. (This is because in the background the default Jersey client will use URL.openConnection) Now you can work around this by using the Apache HTTP Client adapter for Jersey; but this is not always available. So if you want to use the Jersey client with cookies in a server environment you need to do a little bit of reflection to ensure you use your own private cookie jar. final CookieHandler ch = new CookieManager(); Client client = new Client(new URLConnectionClientHandler( new HttpURLConnectionFactory() { @Override public HttpURLConnection getHttpURLConnection(URL uRL) throws IOException { HttpURLConnection connect = (HttpURLConnection) uRL.openConnection(); try { Field cookieField = connect.getClass().getDeclaredField("cookieHandler"); cookieField.setAccessible(true); MethodHandle mh = MethodHandles.lookup().unreflectSetter(cookieField); mh.bindTo(connect).invoke(ch); } catch (Throwable e) { e.printStackTrace(); } return connect; } })); This will only work if your environment is using the internal implementation ofsun.net.www.protocol.http.HttpURLConnection that comes with the JDK. This appears to be the case for modern versions of WLS. For JAX-RS 2.0 you can do a similar change using Jersey 2.x specific ClientConfig classand HttpUrlConnectorProvider. final CookieHandler ch = new CookieManager(); Client client = ClientBuilder.newClient(new ClientConfig().connectorProvider(new HttpUrlConnectorProvider().connectionFactory(new HttpUrlConnectorProvider.ConnectionFactory() { @Override public HttpURLConnection getConnection(URL uRL) throws IOException { HttpURLConnection connect = (HttpURLConnection) uRL.openConnection(); try { Field cookieField = connect.getClass().getDeclaredField("cookieHandler"); cookieField.setAccessible(true); MethodHandle mh = MethodHandles.lookup().unreflectSetter(cookieField); mh.bindTo(connect).invoke(ch); } catch (Throwable e) { e.printStackTrace(); } return connect; } })));

February 24, 2015

· 7,337 Views · 0 Likes

Missing Stack Traces for Repeated Exceptions

A long while ago a optimisation was added to the JVM so that if the same exception is thrown again and again and again a single instance of the Exception is created without the stack trace filled in in order to increase performance. This is an excellent idea unless you are trying to diagnose a problem and you have missed the original error. If you forgot about this optimisation you send the afternoon looking at the following log output and weeping slightly. (In my defence I have a little one in the house hence the fuzzy brain and lack of blogging action this year) java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException java.lang.ArrayIndexOutOfBoundsException ... java.lang.Exception: Uncaught exceptions during test at oracle.jdevstudio-testware-tests.level0.testADFcMATS(/.../work/mw9111/jdeveloper/jdev/extensions/oracle.jdevstudio-testware-tests/abbot/common-adf/CreateNewCustomAppAndProjectWithName.xml:25) at oracle.jdevstudio-testware-tests.level0.testADFcMATS(/.../work/mw9111/jdeveloper/jdev/extensions/oracle.jdevstudio-testware-tests/abbot/level0/testADFcMATS.xml:94) at oracle.abbot.JDevScriptFixture.runTest(JDevScriptFixture.java:555) at junit.framework.TestCase.runBare(TestCase.java:134) at junit.framework.TestResult$1.protect(TestResult.java:110) at junit.framework.TestResult.runProtected(TestResult.java:128) at junit.framework.TestResult.run(TestResult.java:113) at junit.framework.TestCase.run(TestCase.java:124) at junit.framework.TestSuite.runTest(TestSuite.java:243) at junit.framework.TestSuite.run(TestSuite.java:238) at junit.textui.TestRunner.doRun(TestRunner.java:116) at junit.textui.TestRunner.doRun(TestRunner.java:109) at oracle.abbot.AbbotRunner.run(AbbotRunner.java:614) at oracle.abbot.AbbotAddin$IdeAbbotRunner.run(AbbotAddin.java:634) at java.lang.Thread.run(Thread.java:745) Caused by: java.lang.ArrayIndexOutOfBoundsException [Crickets] It turns out that you can turn off this optimisation with a simple flag: java -XX:-OmitStackTraceInFastThrow .... In my particular case the actual exception causing this trouble was a NPE from the GlyphView code in JDK8. (One that is being caused by a glitch in hotspot it seems) But that in turn was causing the AIOOBE in some logging code clouding the issue even more. This in particular is a good flag to add by default when running your automated tests, particularly in combination with the stack trace length override I have talked about before.

November 9, 2014

· 10,443 Views · 1 Like

Using UriTemplate to Change Path Parameters in a URI

I have been recently working on a client generator in the wadl.java.net project and I was solving a bug where I wanted to change path parameter on a URI. This turned out to be quite easy with existing classes that are part of the Jersey project. First of all you need a instance of UriTemplate, depending on the very of Jersey this is in a slightly different package - you IDE's automatic import will do the work for you. String template = "http://example.com/name/{name}/age/{age}"; UriTemplate uriTemplate = new UriTemplate(template); Then you use match(...) to extract them: String uri = "http://example.com/name/Bob/age/47"; Map parameters = new HashMap<>(); // Not this method returns false if the URI doesn't match, ignored // for the purposes of the this blog. uriTemplate.match(uri, parameters); Then you can replace the parameters at will and rebuild the URI: parameters.put("name","Arnold"); UriBuilder builder = UriBuilder.fromPath(template); URI output = builder.build(parameters);

March 1, 2013

· 41,387 Views · 1 Like

JSON-Schema in WADL

In between other jobs I have recently been reviewing the WADL specification with a view to fixing some documentation problems and to producing an updated version. One of the things that was apparent was the lack of any grammar support for languages other than XML - yes you can use a mapping from JSON<->XML Schema but this would be less than pleasant for a JSON purist. So I began to look at how one would go about attaching a JSON-Schema grammar of a JSON document in a WADL description of a service. This isn't a specification yet; but a proposal of how it might work consistently. Now I work with Jersey mostly, so lets consider what Jersey will currently generate for a service that returns both XML and JSON. So the service here is implemented using the JAX-B binding so they both use a similar structure as defined by the XML-Schema reference by the include. So the first thing we considered was re-using the existing element property, which is defined as a QName, on the representation element to reference an imported JSON-Schema. It is shown here both with another an arbitrary namespace so it can be told apart from XML elements without a namespace. Or xmlns:json="http://wadl.dev.java.net/2009/02/json" The problem is that the JSON-Schema specification as it stands doesn't have a concept of a "name" property, so each JSON-Schema is uniquely identified by its URI. Also from my read of the specification, each JSON-Schema contains the definition for at most one document - not the multiple types / documents that can be contained in XML-Schema. So the next best suggestion would be to just use the "filename" part of the URI as a proxy for the URI; but of course that won't necessarily be unique. I could see for example the US government and Yahoo both publishing there own "address" micro format. The better solution to this problem is to introduce a new attribute, luckily the WADL spec was designed with this in mind, that is a type of URI that can be used to directly reference the JSON-Schema definitions. So rather than the direct import in the previous example we have a URI property on the element itself. The "describedby" attribute name comes from the JSON-Schema proposal and is consistent with the rel used on atom links in the spec. xmlns:json="http://wadl.dev.java.net/2009/02/json-schema" xmlns:m="urn:message" The secondary advantage is that this format is backward-compatible with tooling that was relying on the XML-Schema grammar. Although this is probably only of interest to people who work in tooling / testing tools like myself. Once you have the JSON-Schema definition then some users are going to want to do away with the XML all together, so finally here is a simple mapping of the WADL to a JSON document that contains just the JSON-Schema information. It has been suggested by Sergey Breyozkin that the JSON mapping would only show the json grammars and I am coming around to that way of thinking. I would be interested to hear of a usecase for the JSON mapping that would want access to the XML Schema. { "doc":{ "@generatedBy":"Jersey: 1.16-SNAPSHOT 10/26/2012 09:28 AM" }, "resources":{ "@base":"http://localhost/", "resource":{ "@path":"/root", "method":{ "@id":"hello", "@name":"PUT", "request":{ "representation":[ { "@mediaType":"application/json", "@describedby":"application.wadl/requestMessage" } ] }, "response":{ "representation":[ { "@mediaType":"application/json", "@describedby":"application.wadl/responseMessage" } ] } } } } } I am currently using the mime type of "application/vnd.sun.wadl+json" for this mapping to be consistent with the default WADL mime type. I suspect we would want to change this in the future; but it will do for starters. So this is all very interesting but you can't play with it unless you have an example implementation. I have something working for both the server side and for a Java client generator in Jersey and wadl2java respectively, and that will be the topic of my next post. I have been working with Pavel Bucek and the Jersey team on these implementations and the WADL proposal. Thanks very much to him for putting up with me.

December 17, 2012

· 38,170 Views · 1 Like

Comments

How Java 8 Binds Generic Types to Method References

Aug 23, 2016 · Duncan Brown

Looks like based on the language spec this is unresolvable.

https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.13.1

How Java 8 Binds Generic Types to Method References

Aug 23, 2016 · Duncan Brown

Sure, I use them in other posts but they would look something like this:

@FunctionalInterface
public interface ThrowingSupplier<T, E extends Exception> {

T get() throws E;
}

@FunctionalInterface
public interface ThrowingFunction<T, R, E extends Exception> {

R apply(T v) throws E;
}

How Java 8 Binds Generic Types to Method References

Aug 23, 2016 · Duncan Brown

Yes sorry about that, I made the mistake when doing a final consistency tidy up before I posted, there is acually a interesting error as the problem is that I was very unlucky to have:

1. A instance of type Integer has a method that returns a String

2. A static method that take a int and return a string.

Both of these are valid matches and since you cannot specify the overloaded parameters for a method reference, well hence the compile error.

I was just very unlucky with the example I picked, I haven't yet figured out a way to resolve the first one, I will think on it some more.

Remembering to Reset Thread Context Class Loader

Aug 15, 2016 · Alan Hohn

We used a standard ThrowableFunction<T,E>() because in JDK 8 the compiler can work out the most specific excpeiton thrown and bind to E when calling the enclusore, this prevents all calling code having toe deal with "Exception" rathern than say IOException.

This would means your jDK 8 example should look like this:

returnedClassLoaderString = ClassLoaderSwitcher.executeActionOnSpecifiedClassLoader(

urlClassLoader, this::mightThrowException);

Although passing in a class to provide the classloader context is sometimes more useful.

returnedClassLoaderString = ClassLoaderSwitcher.executeActionOnSpecifiedClassLoader(

someClass, this::mightThrowException);

Why Does JavaScript Loop Only Use the Last Value?

Jun 23, 2016 · Dave Fecak

Just use a forEach to capture the context:

_.range(0,10).forEach(function (i) {
setTimeout(function(){
console.log(i);
},1000);
});

Much simpler and uses standard notation.

Lambda of Lambda, if/Else From an Optional

Mar 14, 2016 · Dave Fecak

Fair comment, I wil update the original blog, thanks for the pointer.

Useful OpenID Provider for internal installations

May 28, 2013 · Prabath Siriwardena

It looks like you are right, thanks for the link.

Gerard

Useful OpenID Provider for internal installations

May 28, 2013 · Prabath Siriwardena

It looks like you are right, thanks for the link.

Gerard

Using Java WebSockets, JSR 356, and JSON mapped to POJO's

May 28, 2013 · Allen Coin

It looks like you are right, thanks for the link.

Gerard

Using Java WebSockets, JSR 356, and JSON mapped to POJO's

May 28, 2013 · Allen Coin

It looks like you are right, thanks for the link.

Gerard

Lightweight Live Online User Count WebControl for ASP.NET

May 23, 2013 · Yoann Besson

Hi,

You say that @PathParam can only be of type string, this is a mistake in the spec. You can also use primitive and boxed primitive types, see this issue:

https://java.net/jira/browse/WEBSOCKET_SPEC-200

Cheers,

Gerard

JSR 356, Java API for WebSocket

May 23, 2013 · James Sugrue

Hi,

You say that @PathParam can only be of type string, this is a mistake in the spec. You can also use primitive and boxed primitive types, see this issue:

https://java.net/jira/browse/WEBSOCKET_SPEC-200

Cheers,

Gerard

Useful OpenID Provider for internal installations

May 14, 2013 · Prabath Siriwardena

Jason,

Nothing special but sometimes I use it when crossing over to a different meta level. So when you end up doing reflection to you have $someField for the Field object that represents a give field and someField for the actual value of that field.

It also helps a lot when writing code generators to make this distinction; but that is a far less common use case.

Gerard

Using Java WebSockets, JSR 356, and JSON mapped to POJO's

May 14, 2013 · Allen Coin

Jason,

It also helps a lot when writing code generators to make this distinction; but that is a far less common use case.

Gerard

Useful OpenID Provider for internal installations

May 10, 2013 · Prabath Siriwardena

Vidhya,

Appart from a main method to wrap the final two snippets there is no other code. This is a slight escaping issue in the EchoBeanClient that I have asked the DZone people to fix; but otherwise all the code is there.

Gerard

Using Java WebSockets, JSR 356, and JSON mapped to POJO's

May 10, 2013 · Allen Coin

Vidhya,

Gerard

Marco Casario,hands on Adobe world: Why Java developers should learn and use Flex 2

Nov 12, 2009 · Gerd Storm

Rainer,

Thanks for your reply, I do have to call you up on two points though.

First of all JDeveloper is not based on a JBuilder kernel, this was true in the early versions which use the JBuilder hybrid IDE written in Java,C,Pascal, Asembler and chicken entrails*. Since version 5.0 of JDeveloper we have used a new tool base re-written in Java. I will claim to be an authoritative person on this as I have worked on Oracle tools on and off for over a decade now. (Yes there are some classes with similar names; but that is to be expected given the heritage)

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

You can also work with over databases so you are not entirely stuck in the Oracle world with ADF. Part of the reason for this flexibility is that ADF is the basis for upcoming Fusion Applications which can be deployed to different application servers etc.

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

You will have to excuse my enthusiasm for ADF, I guess this seems like a bit of astro turfing on my part, the tools org in Oracle has been given on day a week out of there normal duties to build interesting ADF applications. I had never played much with ADF in anger to until they started us all on courses and I was pleasantly supprised how easy it was to use.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Marco Casario,hands on Adobe world: Why Java developers should learn and use Flex 2

Nov 12, 2009 · Gerd Storm

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Marco Casario,hands on Adobe world: Why Java developers should learn and use Flex 2

Nov 12, 2009 · Gerd Storm

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Marco Casario,hands on Adobe world: Why Java developers should learn and use Flex 2

Nov 12, 2009 · Gerd Storm

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Java Can Be Saved

Nov 12, 2009 · Jeff Martin

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Java Can Be Saved

Nov 12, 2009 · Jeff Martin

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Java Can Be Saved

Nov 12, 2009 · Jeff Martin

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Java Can Be Saved

Nov 12, 2009 · Jeff Martin

Rainer,

Thanks for your reply, I do have to call you up on two points though.

It is also worth mentioning that the ADF components can be deployed to other JEE application servers / even just plain Tomcat:

http://blogs.oracle.com/dana/2009/01/how_to_deploy_a_11g_adf_applic_1.html

http://www.oracle.com/technology/products/jdev/htdocs/11/database.html

You might find that ADF is interesting even in cases where you are using a different database and application servers.

Anyway, enough rambling back to my day job

Gerard

Oracle JDeveloper WebService / Spring / SCA Lite tooling

* This was a nightmare to maintain but apparently required to get the right perfromance in a java ide.

Marco Casario,hands on Adobe world: Why Java developers should learn and use Flex 2

Nov 11, 2009 · Gerd Storm

What about frameworks such as Oracle ADF:

http://www.oracle.com/technology/products/adf/index.html

Most simple web apps are drag and drop operations that build JSF apps. I would guess I could take someone from school have have them productively building apps in only a few months.

Of course disclaimer, I work on the JDeveloper product; but not ADF directly.

Gerard

Java Can Be Saved

Nov 11, 2009 · Jeff Martin

What about frameworks such as Oracle ADF:

http://www.oracle.com/technology/products/adf/index.html

Most simple web apps are drag and drop operations that build JSF apps. I would guess I could take someone from school have have them productively building apps in only a few months.

Of course disclaimer, I work on the JDeveloper product; but not ADF directly.

Gerard