Handle Applet throwing java.lang.ExceptionInInitializerError preventing it from running

Question

We are developing java applet and embedding it in our web pages. When the applet is loaded via HTML APPLET tags, the browser/JVM prompts the user to allow it to run. When we hit cancel, the java console indicates the following exception:

java.lang.RuntimeException: java.lang.ExceptionInInitializerError
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ExceptionInInitializerError
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$12.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.security.AccessControlException: access denied (java.lang.RuntimePermission getenv.TEMP)
    at java.security.AccessControlContext.checkPermission(Unknown Source)
    at java.security.AccessController.checkPermission(Unknown Source)
    at java.lang.SecurityManager.checkPermission(Unknown Source)
    at java.lang.System.getenv(Unknown Source)
    at downLoadApp.<clinit>(downLoadApp.java:15)
    ... 21 more
Exception: java.lang.RuntimeException: java.lang.ExceptionInInitializerError

Now, I realize it's most likely because the class java tried to load was prevented from loading, and therefore the exception is thrown, but how do we gracefully handle this situation in the browser? I'd like to detect that the applet was denied and post a reasonable response to the condition, but I'm unaware of how to catch this exception since it appears to have been thrown by the JVM in reaction to not getting the jar file to load rather than code written in it...

Ideas?

Thanks!

Answer 1

You can catch the access control exception by putting the call to System.getenv in downLoadApp.java line 15 in a try-catch statement. That is, instead of this:

static String tmp = System.getenv("TEMP");

you should have:

static String tmp;

static {
    try {
        tmp = System.getenv("TEMP");
    } catch (java.security.AccessControlException ace) {
        // tmp is not set, maybe use some default value?
    }
}

Answer 2

Do you call System.getenv("TEMP") somewhere in the static context of the downLoadApp class? Most probably this is in the initializer of a static field, but it could be in a static code block.

This is the place where it fails (a java.security.AccessControlException is thrown). The rest of the stack trace are errors following from that. You need to catch this exception to detect that you don't have the appropriate permissions.

As you can't catch exceptions of static field initializers, you need to move the call to getenv into a method or a static code block.

Answer 3

我认为您无法捕获此异常，因为JVM在加载小程序时抛出了此异常。