cant catch NoClassDefFoundError

[Mike Kowalski]

Hi.
This is my code:

    try {
            final BasicService bs;
            final URL codeBase;
            try {
                bs = (BasicService) ServiceManager.lookup(
                        "javax.jnlp.BasicService");
                codeBase = bs.getCodeBase();
                System.out.println(codeBase);
            } catch (UnavailableServiceException ex) {
                Logger.getLogger(applet.class.getName()).log(Level.SEVERE, null, ex);
            }
        } catch (Exception catchMe) {
        }

and i get:

java.lang.NoClassDefFoundError: javax/jnlp/UnavailableServiceException
Caused by: java.lang.ClassNotFoundException: javax.jnlp.UnavailableServiceException
	at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
Exception in thread "main" Java Result: 1

I know that this code will only work when i lunch my app using JWS, but is there a way to catch the exception if i lunch my app using jar archiwe? I need this to find out if user is lunching my app localy (using jar archiwe) instead of lunching it through jnlp file.

Thank you very much for your time

[Jacob Anawalt]

NoClassDefFoundError seems to be uncatchable because you get tripped up twice. First javax.jnlp.ServiceManager.lookup triggers the NoClassDefFoundError, but the enclosing try/catch also contains an undefined class, javax.jnlp.UnavailableServiceException.

Since those are Errors, it is generally discouraged to try and catch them anyway, so lets find another way.

I don't know the canonical way of testing if Java Web Start is active or not, but using java.lang.Class.forName seems like a good way to throw a java.lang.ClassNotFoundException instead.

    try {
            Class sm = Class.forName("javax.jnlp.ServiceManager");
            final BasicService bs;
            final URL codeBase;
            try {
                bs = (BasicService) ServiceManager.lookup(
                        "javax.jnlp.BasicService");
                codeBase = bs.getCodeBase();
                System.out.println(codeBase);
            } catch (UnavailableServiceException ex) {
                Logger.getLogger(applet.class.getName()).log(Level.SEVERE, null, ex);
            }
        } catch (Exception catchMe) {
           // will catch the ClassNotFoundException here if not running under web start / jnlp / javaws.jar
        }