ClassNotFoundException with ant's java task and classpath

Question

Hello,

I am trying to compile and run a simple java class within eclipse. The compile task works fine, and since I do not specify a destination folder the build files are in the same directory as the source. Which is alright, at the moment all I need is to learn how I can run the class with the main() method.

I have tried using the fully qualified name of the class (with package name, etc) and the classname alone, but always I get a java.lang.ClassNotFoundException

    Buildfile: C:\Users....\build.xml
    run:
         [java] java.lang.NoClassDefFoundError: code/control/MyClass
         [java] Caused by: java.lang.ClassNotFoundException: code.control.MyClass
         [java]     at java.net.URLClassLoader$1.run(Unknown Source)
         [java]     at java.security.AccessController.doPrivileged(Native Method)
         [java]     at java.net.URLClassLoader.findClass(Unknown Source)
         [java]     at java.lang.ClassLoader.loadClass(Unknown Source)
         [java]     at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
         [java]     at java.lang.ClassLoader.loadClass(Unknown Source)
         [java]     at java.lang.ClassLoader.loadClassInternal(Unknown Source)
         [java] Could not find the main class: code.control.MyClass.  Program will exit.
         [java] Exception in thread "main" 
         [java] Java Result: 1
    compile:
    default:
    BUILD SUCCESSFUL
 Total time: 234 milliseconds

Below, are the targets taken from my build.xml file:

<target name="default" depends="compile" description="learn">

</target>

  <target name="compile" depends="run">
            <javac srcdir="src/" />
   </target>

  <target name="run">
  <java classname="code.control.MyClass" fork="true"/>
</target>

I can't figure out why the class is not found. MyClass contains the main() method and since i specify no classpath it should look at the current directory, which is the src/ right?

The development directory is the usual eclipse file structure:

projectName/src/code/control/MyClass

If it is a classpath problem how could I resolve it? I always had problem grasping the concept "put it on your classpath" ... If someone could provide a little bit of explanation with the classpath in the ant context, I would be very thankful.

Thanks for any help on this. The version of ant is 1.7.0

Answer 1

The classpath is where the Java runtime looks for your .class files, similar to how your OS uses the PATH variable to find executables.

Try this in your build script:

   <target name="run">
    <java fork="true" classname="code.control.MyClass">
        <classpath>
            <path location="src/"/>
        </classpath>
    </java>

There's a HelloWorld version for ant that walks through building a Java program with ant.

Answer 2

you should include classpath, e.g.

<java classpath="${bin}" classname="code.control.MyClass">

where ${bin} is your output folder.

Answer 3

I think you want to change your depends clause:

. . . . . .

Answer 4

hi..........everyone...........i am running java program thorgh ant using exec command..

but if classname or classpath is worng then in the output i am getting exception .and if everything is classname and classpath is correct am getting correct output.....my question how to determine the exception in ant?..........if anyone knows give d ans with code.....its realy urgent.........thanks.......