Why do I get “A Java Exception has occurred” after I export my application to Jar?

问题

Well, I exported my application into JAR with eclipse, but now whenever I try running it I get the: "A Java Exception has occurred". When I try to run it through command line it says:

C:\Users\Arturas>java -jar D:\Dropbox\EclipseWorkspace\Exports\Dantracio_skaiciu
oklis3.jar
Exception in thread "main" java.lang.NoClassDefFoundError: org/eclipse/swt/widge
ts/Composite
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)
        at sun.launcher.LauncherHelper.getMainMethod(Unknown Source)
        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.eclipse.swt.widgets.Composite
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 6 more

C:\Users\Arturas>

Any solutions to this? I just hate java for this... It never works on desktops when you want it to... sorry I'm really stressed out from this, I'm overreacting...

Any ideas what could cause this? I doesn't work on other computers as well. Right now it's using Java 1.7. And the application runs perfectly on Eclipse.

回答1:

You need to get your dependencies. Looks like you are depending on swt, which is not part of the core java language. You'll need to get all the third party jars that you depend on and include them in your classpath. It runs perfectly on eclipse because eclipse takes care of setting up the classpath for you.

You can set the classpath in your manifest file as described in the documentation, or you could include a script to start your application that will use the -cp command when running the jar, or you can use something that will package everything into one monster jar like the solutions to this question.

来源：https://stackoverflow.com/questions/13078505/why-do-i-get-a-java-exception-has-occurred-after-i-export-my-application-to-ja