java.lang.ClassNotFoundException when running java -jar

Question

I'm using ant to build my build.xml file, it compiles ok, but then getting a runtime java.lang.NoClassDefFoundError when running the resulting jar via "java -jar my_jar.jar". It seems like this comes up a lot but none of the related questions' solutions worked for me.

My classpath for javac contains only "/usr/local/lib/libthrift.jar" and the main .java file imports a bunch of thrift packages such as org.apache.thrift.transport.TTransportException.

When I try running the program via:

java -jar MyClass.jar

, I get the error:

Exception in thread "main" **java.lang.NoClassDefFoundError**: org/apache/thrift/transport/TTransportException
Caused by: java.lang.ClassNotFoundException: org.apache.thrift.transport.TTransportException
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
Could not find the main class: **MyClass**. Program will exit.

Here are the things I've tried so far that don't work:

• adding a flag on the command line like "java -cp /usr/local/lib/libthrift.jar -jar my_jar.jar", the result is the same error as above

• adding <attribute name="Class-Path" value="./:/usr/local/lib/libthrift.jar"/> inside my jar's manifest> tag, the result is the same error as above

• adding -Xbootclasspath/a:/usr/local/lib/libthrift.jar:./ to the java command line. it solves the first error but a different error comes up:

  Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/log4j/Logger at org.apache.thrift.transport.TServerSocket.<clinit>(TServerSocket.java:36) at MyClass.start(Unknown Source) at MyClass.main(Unknown Source)

EDIT:

If I comment out the code that instantiates the missing classes but leave the imports, the code executes fine.

EDIT:

I moved my java classes to a server and referenced the MainClass with the server in the manifest attribute, but that didn't fix anything.

Answer 1

Could not find the main class: MyClass

The error seems actually related to your MANIFEST which:

• may not have a complete classpath Class-Path: see this HowTo

The best solution when you have a jar is to try to include the required jars into the manifest declaration.

Manifest-Version: 1.0 
Class-Path:  
 customer_client.jar  
 mailer_client.jar  
 signon_client.jar 

• or may not define adequately the MainClass within your 'my_jar.jar'.

See this HowTo:

<target name="jar" depends="compile">
     <delete file="hello.jar"/>
     <delete file="MANIFEST.MF"/>
     <manifest file="MANIFEST.MF">
        <attribute name="Built-By" value="${user.name}"/>
        <attribute name="Main-Class" value="howto.Hello"/>
    </manifest>

      <jar destfile="hello.jar"
           basedir="."
           includes="**/*.class"
           manifest="MANIFEST.MF"
           />
  </target>

the <attribute name="Main-Class" value="howto.Hello"/> needs to specify the full path (packages) of the MainClass, not just MainClass.

If your main class is in the default package (the unnamed package), I am not sure it can be referenced by the loader (see this SO question)
So move your JarRunner into a package, and declare it appropriately in the <attribute name="Main-Class" value="myPackage.JarRunner"/> element.