NoClassDefFoundError without any class name_问答_开发者

I am trying to run a java task from ant. I am trying to run the "org.apache.tools.ant.launch.Launcher" class. I keep on getting the "NoClassDefFoundError" without any class name being specified. I am also getting a "ClassNotFoundException" along with that displaying a message "Could not find the main class: . Program will exit". Here's a snippet of the error

 [java] Exception in thread "main" java.lang.NoClassDefFoundError: 
 [java] Caused by: java.lang.ClassNotFoundException: 
 [java]  at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
 [java]  at java.security.AccessController.doPrivileged(Native Method)
 [java]  at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
 [java]  at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
 [java]  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
 [java]  at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
 [java]  at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
 [java] Could not find the main c开发者_如何转开发lass: .  Program will exit.
 [java] Java Result: 1

Now I am trying to run an ant class from an ant jar and i specifiy the classpath where this class file resides using the "classpathref" attribute, however I still get this message. I checked the ant jar to check the Manifest and the "main" class is specified properly (it's "org.apache.tools.ant.launch.Launcher") . I have exhausted all my resources. Please help ! ! !

ps: My environment is Eclipse on Ubuntu 9.04

Most likely your classpath is misconfigured.

At a minimum the CLASSPATH should include:

ant.jar and ant-launcher.jar
jars/classes for your XML parser
the JDK's required jar/zip files

(from the ant manual)

Also you seem to be relaunching ant in the current directory (executing the same build.xml). Maybe you'll want to set the "dir" property.

It looks like the Ant task is trying to run Java, but is somehow passing an empty string to the JVM as the name of the class to run. I can get the same stacktrace if I run the JVM directly with a quoted empty string:

C:\>java ""
Exception in thread "main" java.lang.NoClassDefFoundError:
Caused by: java.lang.ClassNotFoundException:
        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)
Could not find the main class: .  Program will exit.

(This is on Windows, but I don't think that makes much of a difference.)

I can only suggest following up on Alexander Pogrebnyak's comment to akf's answer. Perhaps the webtest.lib property has spaces in it?

Also, is there a good reason for calling ant directly via java, rather than using the ant task?

https://blogs.oracle.com/sreekanth/entry/java_lang_noclassdeffounderror_org_codehaus

java.lang.NoClassDefFoundError: org/codehaus/plexus/classworlds/launcher/Launcher
By sreekanth on Nov 23, 2010

Recently when I am trying to run some Maven scripts, I am getting this exception:

Exception in thread "main" java.lang.NoClassDefFoundError: org/codehaus/plexus/classworlds/launcher/Launcher

Caused by: java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher
 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)

Could not find the main class: org.codehaus.plexus.classworlds.launcher.Launcher.  Program will exit.

After spending some time trying various combinations , I found that this is because I have both M2_HOME and M3_HOME set in my environment variables.Once I removed M2_HOME from my environment variables, I could get this working back again.May be this could save some serious time for some one.

This can be a misleading error that is not actually about a class missing from the classpath. If you are using Tomcat it can be due to missing conf files in $CATALINA_BASE/conf

It could also be a misconfigured ant installation, please check your JAVA_HOME and ANT_HOME env variables or try another ant installation.

Ant launcher expects the following params

java -Dant.home=c:\ant org.apache.tools.ant.launch.Launcher [options] [target]

I am affraid we can't proceed answering you if you don't paste your whole build.xml file.

Just try to give your full sample as below:

   <java
            classname="org.apache.tools.ant.launch.Launcher"
            fork="true"
            failonerror="true"
            dir="${sub.builddir}"
            timeout="4000000"
            taskname="startAnt"
    >
        <classpath>
            <pathelement location="${ant.home}/lib/ant-launcher.jar"/>
        </classpath>
        <arg value="-buildfile"/>
        <arg file="${sub.buildfile}"/>
        <arg value="-Dthis=this"/>
        <arg value="-Dthat=that"/>
        <arg value="-Dbasedir=${sub.builddir}"/>
        <arg value="-Dthe.other=the.other"/>
        <arg value="${sub.target}"/>
 </java>

This would be extremely helpful to provide you with a possible misunderstanding.

Hope this helps,

Ernani

From this line:

[java] Could not find the main class: .  Program will exit.

it looks as though your call to java.exe is finding a . where it expects a class name. Perhaps you are trying to indicate the classpath on the commandline but are neglecting to preface that with the -cp or -classpath flag.

When in doubt, invoke ant -v and watch all your variable declarations, and the whole commandline sent to Java.

Certain path-like quantities are eagerly evaluated, while others are lazily evaluated. I've had plenty of problems where I used one of the former, when my Ant script intended to create a jar that would be used by a later task. Then by the time I invoked the call, it had already pruned my jar from the classpath.

If I had to make a wild guess, I'd bet your commandline looked something like:

java ... -classpath org.apache.tools.ant.launch.Launcher

instead of

java ... -classpath foo.jar;bar.jar org.apache.tools.ant.launch.Launcher

like you expected

I had a similar problem recently. The culprits were 2 tags under the java task, that didn't have their values set, so they resulted in 2 empty command arguments and in the end in 2 spaces in the command line. For some reason Unix doesn't handle it right. Both Red Hat 5 and Ubuntu displayed the same error. It was OK on Windows 7. Setting those arguments to have default dummy values solved the issue.