GWT/ Eclipse: ClassNotFoundException com/google/gw

问题:

i recently updated from GWT 2.0.4 to 2.1.0. Since then I cannot compile my GWT application anymore. When I click on the GWT compile button of the GWT eclipse plugin I get the following error:

java.lang.NoClassDefFoundError: com/google/gwt/dev/Compiler
Caused by: java.lang.ClassNotFoundException: com.google.gwt.dev.Compiler
 at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
 at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Exception in thread "main"

Also I can't create a new GWT project in Eclipse. In the new New Web Application Project Dialog one can choose to use GWT and/or Google App Engine. When check "Use GWT" a error dialog raises up which says: "Creation of element failed. Reason: Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details."

In the log file (<workspace>/.metadata/.log) I can see the message:

!ENTRY org.eclipse.jdt.ui 4 10001 2010-11-02 08:34:50.085
!MESSAGE Internal Error
!STACK 1
Java Model Exception: Core Exception [code 0] Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.
 at org.eclipse.jdt.internal.core.BatchOperation.executeOperation(BatchOperation.java:50)
 at org.eclipse.jdt.internal.core.JavaModelOperation.run(JavaModelOperation.java:728)
 at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
 at org.eclipse.jdt.core.JavaCore.run(JavaCore.java:4777)
 at org.eclipse.jdt.internal.ui.actions.WorkbenchRunnableAdapter.run(WorkbenchRunnableAdapter.java:106)
 at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
Caused by: org.eclipse.core.runtime.CoreException: Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.
 at com.google.gwt.eclipse.core.runtime.tools.WebAppProjectCreatorRunner.createProject(WebAppProjectCreatorRunner.java:53)
 at com.google.gdt.eclipse.suite.wizards.WebAppProjectCreator.createGWTProject(WebAppProjectCreator.java:532)
 at com.google.gdt.eclipse.suite.wizards.WebAppProjectCreator.create(WebAppProjectCreator.java:294)
 at com.google.gdt.eclipse.suite.wizards.NewWebAppProjectWizard.finishPage(NewWebAppProjectWizard.java:147)
 at org.eclipse.jdt.internal.ui.wizards.NewElementWizard$2.run(NewElementWizard.java:117)
 at org.eclipse.jdt.internal.core.BatchOperation.executeOperation(BatchOperation.java:39)
 at org.eclipse.jdt.internal.core.JavaModelOperation.run(JavaModelOperation.java:728)
 at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1975)
 at org.eclipse.jdt.core.JavaCore.run(JavaCore.java:4777)
 at org.eclipse.jdt.internal.ui.actions.WorkbenchRunnableAdapter.run(WorkbenchRunnableAdapter.java:106)
 at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
!SUBENTRY 1 com.google.gwt.eclipse.core 4 0 2010-11-02 08:34:50.085
!MESSAGE Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details.

gwt-dev.jar, gwt-user.jar and many other google-jars are in the classpath...

Does anyone have an idea how to solve this issue? I also set up a new fresh Eclipse installation, installed the new GWT plugin, and chose a new workspace directory, but this still gives me the errors...

Additional information:

• Windows XP,
• Eclipse for Java EE 3.6 Helios,
• J2EE / Java 1.6.0_22-b04
• Google Plugin for Eclipse 3.6 1.4.0.v201010280102,
• Google App Engine Java SDK 1.3.8 1.3.8.v201010161055
• Google Web Toolkit SDK 2.1.0 2.1.0.v201010280102

回答1:

I had the same problem not being able to create a new GWT-project in Eclipse. Removing the Classpath variable from my windows environment variables (appearently interfering with the settings in Eclipse) solved the problem for me.

回答2:

In my case the jar (gwt-dev-2.1.0.jar) downloaded from the google maven repo was corrupt! I replace the jar in my repo with a one containing the classes and mvn gwt:run worked!

hope this helps.

回答3:

I was facing a similar issue where I was getting constantly java.lang.NoClassDefFoundError: com/google/gwt/dev/Compiler. While searching around I realized that the gwt version was missing a file from inside the gwt-dev folder inside the gwt installation directory.

Actually, I am using maven and gwt 2.5.0 for my project, and I discovered that inside .m2\repository\com\google\gwt\gwt-dev\2.5.0 folder should exist four files in order for gwt compiler to work. Those are

• gwt-dev-2.5.0.jar <-sometimes this is corrupted
• gwt-dev-2.5.0.jar.sha1 <- this one was missing
• gwt-dev-2.5.0.pom
• gwt-dev-2.5.0.pom.sha1

回答4:

Go to your Project Properties / Build Path there move the "GWT library" to the top of the BuildPath.

Now try to recompile again.

回答5:

I just, remove and include again gwt-dev.jar and start to work.

回答6:

I fix that problem doing this:

• remove GWT lib from your project
• update gwt plugins for eclipse
• put the lib back in your project
• Done

回答7:

I had the same problem, some java program had been installed declaring a "ClassPath" environment variable, and invalidating the gwt plugin for ANY version of eclipse, from 3.6 (helios) to 4.2 (juno). Note that environment variables are case-insensitive in Windows OSs. Solution: eliminate the system/user variable declaration and declare the variable in a/the launch script for the concerned program.

回答8:

My understanding is:

When GWT compiles a project, it needs the tool "com.google.gwt.dev.Compiler" (which has a "main" entry point); however, GWT does not use Eclipse project's "build path" setting to find the tool, instead, it looks at OS's "classpath" system variable.

So, I think the solution is to add "D:\Java\GWT\gwt-2.6.1\*;" (my case as example) into "classpath" and restart Eclipse. It works well for me since.