Reflection + libraries java

Question

Edit: this is the Project Setup:

IDE: Eclipse:

Project1 : "Server"

src:
com/mainpackage/main.java
libs:
commons-x-0.jar
PluginInterface.jar

all jar in libs-folder are on the buildpath.

Project2 : "PluginInterface"

src:
com/interfaces/plugininterface

Project3 : "Plugin"

src:
com/package/class1.java - (this implements plugininterface)
libs:
library1.jar
PluginInterface.jar

all jar in libs-folder are on the buildpath

so when i export the Plugin (Project3) i get a jar like this (excluded PluginInterface.jar from export)

com/
com/package/
com/package/class1.class
com/package/class1.java
libs/
libs/library1.jar

library1.jar looks as follows - it is not written by me:

com/
com/stuff/
com/stuff/libclass.java
com/stuff/libclass.class

now i Want to utilize class1 in the "Server" over the Interface:

ClassLoader loader=URLClassLoader.newInstance( 
                new URL[]{new URL("file:path/to/plugin.jar")},
                ClassLoader.getSystemClassLoader()
        );

Class<?> pluginclass = Class.forName("com.package.class1", true, loader);
plugininterface ref = (plugininterface)pluginclass.newInstance();

i can now call methods from class1 using the interface both projects know, because both of them include "PluginInterface.jar" in their buildpath.

THE PROBLEM:

"Server" does not recognize "libclass", because is neither in its path nor did i load the class from the plugin.jar in which the library1 is nested.

how do i access this class if an import as library is not possible at the server?

Thanks for any help!

Edit: just for the sake if someone ever has this Problem again, i'll add the ANT files' build-target that makes it work:

<target name="build">
     <javac destdir="bin" includeantruntime="false" source="1.7" target="1.7">
        <src path="src"/>
        <classpath refid="Plugin.classpath"/>
     </javac>
    <unzip src="${libs}/library1.jar" dest="bin/">
        <patternset>
            <include name="**/*.class"/>
        </patternset>
</unzip>
    <jar destfile="plugin.jar" basedir="bin"></jar> 
</target>

Just copy the contents of the Library-jar into the build directory (in my case ./bin/). it then isn't even necessary to feed the libraryclasses to the Classloader, it finds them when loading the Classes use them.

Answer 1

The standard class loader does not support nested jar files. You could programmatically extract the jar, or write your own classloader which will decompress the nested files on demand. However, you'd be swimming against the current: such packaging is just not recommended. Instead it is recommended to explode the nested jar into its parent. This is, for example, what Maven dependency plugin does, and the default way to publish a Clojure application with Leiningen.

To achieve your goal from Eclipse the best approach seems be this:

1. have Eclipse's Export JAR wizard save the ant build scripts it internally generates to build your JAR;

2. adapt the resulting script to meet your specific needs;

3. in the future don't run the wizard anymore, but the ant script.