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POGetting an object out of Equinox/Eclipse
 

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  1. POGetting an object out of Equinox/Eclipse
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    <p>I am facing a problem that is a combination of "plain" Java, Equinox, and the communication between the two. I have read other related questions (<a href="https://stackoverflow.com/questions/904050/how-to-run-an-osgi-framework-within-usual-java-code">here</a>, <a href="https://stackoverflow.com/questions/11413235/how-to-get-a-bundle-object-returned-by-a-service-out-of-the-equinox-framework">here</a>, and <a href="https://stackoverflow.com/questions/4673406/programatically-start-osgi-equinox">there</a> as well as other Web sites, such as <a href="http://wiki.osgi.org/wiki/Boot_Delegation" rel="nofollow noreferrer">this one</a> and <a href="http://www.macrobug.com/blog/wp-content/uploads/2009/01/osgiwrapperjava.html" rel="nofollow noreferrer">that one</a>) but could not find a satisfying (or working!) solution.</p> <p>I have a set of plug-ins: P1, P2, and P3. P1 export some classes, which are used by P2. P2 additionally exports other classes and interfaces, which are used by P3. In particular, P2 defines and exports <strong>interface MyInterface</strong> and its implementation <strong>class MyInterfaceImpl implements MyInterface</strong>. P3 is an application and, thus, contains a <strong>class Launcher implements IApplication</strong> and defines the <strong>public Object start(IApplicationContext)</strong> method. Everything compiles fine. When I run the Launcher as an Eclipse application from Eclipse, it runs fine. The launcher uses <strong>MyInterface</strong> and <strong>MyInterfaceImpl</strong> fine.</p> <p>Now, I programmatically run my application using the following (simple) code, which seems to be a "okay" way of running an Equinox/Eclipse application, according to various posts:</p> <pre><code>void callApplication() { final String[] args = new String[] { "-application", "Launcher", ... }; EclipseStarter.run(args, null); } </code></pre> <p>Again, this piece of code works fine and I can "see" my application run and produce its expected results.</p> <p>Now, here comes my problem: I would like to obtain an instance of <strong>MyInterfaceImpl</strong> built by my application, running in Equinox, back inside the "outer" Java code. My naïve solution was to return this object in the <strong>public Object start(IApplicationContext)</strong> method and modify my calling code as follows:</p> <pre><code>MyInterface callApplication() { final String[] args = new String[] { "-application", "Launcher", ... }; return (MyInterface) EclipseStarter.run(args, null); } </code></pre> <p>But this naïve solution does not work. I receive a <strong>java.lang.ClassCastException: MyInterfaceImpl cannot be cast to MyInterface</strong>. Thinking of it, it makes sense because, at the end of <strong>callApplication()</strong>, I have two "versions" of the pairs {<strong>MyInterface</strong>, <strong>MyInterfaceImpl</strong>}: one from the "outer" Java code, loaded by the JVM class-loader, and another from Equinox, loaded by Equinox class-loader. I modified my code to print the class-loaders of the returned object and of <strong>MyInterface</strong>: </p> <pre><code>final Object o = EclipseStarter.run(args, null); System.out.println(o.getClass().getClassLoader()); System.out.println(MyInterface.class.getClassLoader()); </code></pre> <p>and, indeed, I obtained: </p> <pre><code>org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader@7e66458c[P2:1.5.0(id=413)] sun.misc.Launcher$AppClassLoader@1efc3d2 </code></pre> <p>Note that the class-loader of the returned object is said to come from P2, as expected, because P2 is the plug-in that defines and exports <strong>MyInterface</strong> and <strong>MyInterfaceImpl</strong>. </p> <p>I tried different ways to get "compatible" pairs of {<strong>MyInterface</strong>, <strong>MyInterfaceImpl</strong>} but with no luck so far (I always get the same <strong>java.lang.ClassCastException: MyInterfaceImpl cannot be cast to MyInterface</strong>):</p> <ul> <li><p>I tried setting the properties -Dorg.osgi.framework.bootdelegation=* -Dorg.osgi.framework.system.packages.extra=MyInterface,MyInterfaceImpl. </p></li> <li><p>I also tried intercepting the <strong>DefaultClassLoader</strong> in the <strong>start()</strong> method. </p></li> </ul> <p>So, my question is: <em>Is there a way for a Java program, which uses some classes defined in a project, which is also a plug-in and which export these classes, to exchange instances of these classes with an instance of Eclipse started programmatically?</em> Thanks!</p>
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