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Asked: 2026-05-23T08:19:18+00:00

I’m trying to make an applet with jPCT. Using jPCT requires that the jPCT

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I’m trying to make an applet with jPCT. Using jPCT requires that the jPCT jar be added to the classpath. I thought I had it, but I’m still getting a class not found exception about one of jPCT’s classes.

My commands:

$ javac -classpath /var/www/html/jpct.jar:.  /var/www/html/HelloWorld.java
$ jar cf /var/www/html/HelloWorld.jar /var/www/html/HelloWorld.class

My HTML:

<html>
    <head>
        <title>Hello World</title>
    </head>
    <body>
        <applet code="HelloWorld"
              width=640
              height=480
              archive="http://applet/HelloWorld.jar,http://applet/jpct.jar">
        </applet>
    </body>
</html>

I’m using Apache and I have verified that my jars are downloadable from the URLs in my code.

The exact error message:

$ firefox http://applet/HelloWorld.html
java version "1.6.0_22"
OpenJDK Runtime Environment (IcedTea6 1.10.2) (6b22-1.10.2-0ubuntu1~11.04.1)
OpenJDK Server VM (build 20.0-b11, mixed mode)

(firefox-bin:15296): LIBDBUSMENU-GTK-CRITICAL **: dbusmenu_menuitem_property_set_shortcut: assertion `gtk_accelerator_valid(key, modifier)' failed
Unable to use Firefox's proxy settings. Using "DIRECT" as proxy type.
java.lang.NoClassDefFoundError: com/threed/jpct/World
    at HelloWorld.init(HelloWorld.java:18)
    at sun.applet.AppletPanel.run(AppletPanel.java:436)
    at net.sourceforge.jnlp.NetxPanel.run(NetxPanel.java:69)
    at java.lang.Thread.run(Thread.java:679)
Caused by: java.lang.ClassNotFoundException: com.threed.jpct.World
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at net.sourceforge.jnlp.runtime.JNLPClassLoader$CodeBaseClassLoader.findClass(JNLPClassLoader.java:1348)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
    ... 4 more
Exception in thread "TimerQueue" java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:155)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1262)
    at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:459)
    at java.util.concurrent.DelayQueue.take(DelayQueue.java:205)
    at javax.swing.TimerQueue.run(TimerQueue.java:167)
    at java.lang.Thread.run(Thread.java:679)

What am I doing wrong?

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1 Answer

  1. Editorial Team

    You have to put your dependencies on the same web server that is serving the Applet .jar file and give the locations either absolutely or relative to the root context of the Applet.

    And you have to load your Applet into your web browser from the web server, not from the file system.

    Here is the relevant reading materials.

    ARCHIVE = archiveList

    This OPTIONAL attribute describes one
    or more archives containing classes
    and other resources that will be
    “preloaded”. The classes are loaded
    using an instance of an
    AppletClassLoader with the given
    CODEBASE. The archives in archiveList
    are separated by “,”. NB: in JDK1.1,
    multiple APPLET tags with the same
    CODEBASE share the same instance of a
    ClassLoader. This is used by some
    client code to implement inter-applet
    communication. Future JDKs may provide
    other mechanisms for inter-applet
    communication. For security reasons,
    the applet’s class loader can read
    only from the same codebase from which
    the applet was started. This means
    that archives in archiveList must be
    in the same directory as, or in a
    subdirectory of, the codebase. Entries
    in archiveList of the form ../a/b.jar
    will not work unless explicitly
    allowed for in the security policy
    file (except in the case of an http
    codebase, where archives in
    archiveList must be from the same host
    as the codebase, but can have “..”‘s
    in their paths.    )

    if your applet is at /var/www/html/Applet.jar then the simplest thing to do is put your dependencies in the exact same location /var/www/html/jcpt.jar and then you can just refer to it without having to worry about calculating the relative path.

    Example

        <applet code="HelloWorld"
          width=640
          height=480
          archive="HelloWorld.jar,jpct.jar">
    </applet>
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