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Editorial Team
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Asked: 2026-05-14T19:26:28+00:00

I hate starting a post with this but I’m new to Java… I’ve followed

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I hate starting a post with this but I’m new to Java… I’ve followed this tutorial to create a socket server (mines in Eclipse). I can run the server within Eclipse, all is well. But when I try to export the project I can’t figure out how to run it. I keep getting this error (it varies depending on how I run it)

Exception in thread "main" java.lang.NoClassDefFoundError: xsocketserver/Main
Caused by: java.lang.ClassNotFoundException: xsocketserver.Main
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:315)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330)
at java.lang.ClassLoader.loadClass(ClassLoader.java:250)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:398)

I’ve read this problem relates to class paths being set. I’ve tried the following:

java -cp libs/xSocket-2.8.12.jar xsocketserver.Main
java -jar xSocketServer.jar    
java -classpath xSocketServer:xSocketServer/libs/xSocket-2.8.12.jar xsocketserver.Main

plus many others.
The file structure within the JAR is as follows:

xSocketServer.jar
    -> xsocketserver
        -> Main.class
        -> xSocketDataHandler.class
    -> META-INF
        -> MANIFEST.MF
    -> libs
        -> xSocket-2.8.12.jar

Incidentally I’ve tried adding my own manifest file which contains the Class-Path but when I check it it always reads:

Manifest-Version: 1.0
Main-Class: xsocketserver.Main

I’m guessing this is a common problem based on the number of hits I’ve seen in Google but I can’t fathom what I’m doing wrong. Wrong Export settings maybe??

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1 Answer

  1. Editorial Team

    I don’t believe a jar-file can include another jar (as you’ve included xSocket-2.8.12.jar). If xSocket is your own code, let it be included directly in the “outer” jar instead.

    Check out
    http://www.velocityreviews.com/forums/t143595-jars-containing-jars.html
    and
    Classpath including JAR within a JAR

    Otherwise it looks right to me. Make sure you’re not trying to run an old/stale version of the jar. (Delete the jar and make sure eclipse exports a new one.)

    How are you exporting the .jar file from eclipse? The generated jar-file will usually be based on one of your run-configurations. Make sure you use the one that you use when it works from eclipse.

    Unless you’ve already tried it, try following the steps (listed at the site below)

    http://forums.sun.com/thread.jspa?threadID=5358121

    1-Right click on your project and select export option.A export window will get pop-up.

    2-Select jar file option from the poped-up window which will be in java option of window.

    3-After Clicking JarFile option a new window will get pop-up.

    4-Select the export destination for ur jar file and click next.

    5-After clicking the next a new screen you will see, click on next button again.

    6-Now u will see a new screen which has a field name as “Main Class” browse for your main class of appliaction.main class is once which has main method.

    7-Now select finish.

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