Wrong classpath? Why am I still getting NoClassDefFoundError?

Question

I'm writing school's project (discrete simulation library) in Java, and I am still getting this error when I'm running example app:

 [java] Exception in thread "main" java.lang.NoClassDefFoundError: /home/lut/Plocha/IMS/examples/Random/random/RandomTest
 [java] Caused by: java.lang.ClassNotFoundException: .home.lut.Plocha.IMS.examples.Random.random.RandomTest
 [java]     at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
 ...
 [java]     at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
 [java] Could not find the main class: /home/lut/Plocha/IMS/examples/Random/random.RandomTest. Program will exit.
 [java] Java Result: 1

(/home/lut/Plocha/IMS is root directory. In the file tree down here, it's marked as . - dot)

I have library in root directory. There is also directory examples, where are tiny, example applications using this library, each application has it's own build ant script.

The directory structure:

.
├── build.xml   <-- library build-file, examples are not included in this build
├── doc
├── examples
│   ├── Random
│   │   ├── build.xml    <-- example app buil-file
│   │   └── src
│   │       └── random
│   │           └── RandomTest.java  <-- main class of the example
│   └── Calendar
│       ├── build.xml, src, etc. inside
│       ...
├── dest      <-- after library build, dsim.jar is here
├── build
└── src       <-- source files of the library
    └── ims
        ├── Distribution
        │   └── RandomGenerator.java
        ├── Exception
        │   ├── RandomException.java
        │   └── SimulationException.java
        └── SimObjects
            ├── Entity.java
            ├── Event.java
            ├── Facility.java
            ...

I can build both main library (output is dsim.jar in ./dest folder) and example application (in ./examples/Random) without problems, but when I'm then trying to run the example app (ant run), I'm still getting NoClassDefFoundError.

The example app's build.xml (in ./examples/Random) looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<project name="Example - Random generator" default="compile" basedir=".">

  <property name="src"    location="src"/>
  <property name="build"      location="build"/>
  <property name="dest"       location="dest"/>
  <property name="dsim.dir"   location="../../dest"/>
  <property name="dest.jar"   location="${dest}/random.jar"/>
  <property name="main-class" location="random.RandomTest"/>

  <path id="dsim-classpath">
    <fileset dir="${dsim.dir}">
      <include name="*.jar"/>
    </fileset>
  </path>

  <target name="prepare" description="Create necesery directories">
    <mkdir dir="${build}"/>
    <mkdir dir="${dest}"/>
  </target>

  <target name="compile" depends="prepare">
    <javac srcdir="${src}" destdir="${build}" encoding="utf8">
      <classpath refid="dsim-classpath"/>
    </javac>    

    <jar destfile="${dest.jar}" basedir="${build}">
      <manifest>
        <attribute name="Main-Class" value="${main-class}"/>
      </manifest>
    </jar>
  </target>

  <target name="run" depends="compile">
    <java jar="${dest.jar}" fork="true" classpathref="dsim-classpath"/>
  </target>  
</project>

RandomTest.java file starts with lines:

package random;

import ims.Distribution.RandomGenerator;
import ims.Exception.SimulationException;
import ims.SimObjects.Histogram;

public class RandomTest {
    public static void main(String[] args) throws SimulationException {

I tried searching on google, there were several posts about classpath and problems with it, but even though I was not able to determine where could be problem. What am I doing wrong? What I miss?

Thanks a lot.

Answer 1

Ok, so the problem was bad property atribute name (I had location instead of value in main-class property definition).

<property name="main-class" location="random.RandomTest"/>
<!-- shoudl be -->
<property name="main-class" value="random.RandomTest"/>

Then loader finds main class, but another problem appeared: loader cannot find library classes (classes in ./src/)

[java] java.lang.NoClassDefFoundError: ims/Exception/SimulationException
[java] Caused by: java.lang.ClassNotFoundException: ims.Exception.SimulationException

but why? There is classpath reference. Or is it the problem of exclusivity of jar and classpath attribute (comments under frist @duffymo's answer)? How to fix my build.xml to make it work? Thanks.

Answer 2

The class name is random.RandomTest.

What's this?

.home.lut.Plocha.IMS.examples.Random.random.RandomTest

Why is the class loader looking for this?

Here's a generic build.xml that's worked well for me. Create the directory structure and see if it sorts you out:

<?xml version="1.0" encoding="UTF-8"?>
<project name="xslt-converter" basedir="." default="package">

    <property name="version" value="1.6"/>
    <property name="haltonfailure" value="no"/>

    <property name="out" value="out"/>

    <property name="production.src" value="src"/>
    <property name="production.lib" value="lib"/>
    <property name="production.resources" value="config"/>
    <property name="production.classes" value="${out}/production/${ant.project.name}"/>

    <property name="test.src" value="test"/>
    <property name="test.lib" value="lib"/>
    <property name="test.resources" value="config"/>
    <property name="test.classes" value="${out}/test/${ant.project.name}"/>

    <property name="exploded" value="out/exploded/${ant.project.name}"/>
    <property name="exploded.classes" value="${exploded}/WEB-INF/classes"/>
    <property name="exploded.lib" value="${exploded}/WEB-INF/lib"/>

    <property name="reports.out" value="${out}/reports"/>
    <property name="junit.out" value="${reports.out}/junit"/>
    <property name="testng.out" value="${reports.out}/testng"/>

    <path id="production.class.path">
        <pathelement location="${production.classes}"/>
        <pathelement location="${production.resources}"/>
        <fileset dir="${production.lib}">
            <include name="**/*.jar"/>
            <exclude name="**/junit*.jar"/>
            <exclude name="**/*test*.jar"/>
        </fileset>
    </path>

    <path id="test.class.path">                            
        <path refid="production.class.path"/>
        <pathelement location="${test.classes}"/>
        <pathelement location="${test.resources}"/>
        <fileset dir="${test.lib}">
            <include name="**/junit*.jar"/>
            <include name="**/*test*.jar"/>
        </fileset>
    </path>

    <path id="testng.class.path">
        <fileset dir="${test.lib}">
            <include name="**/testng*.jar"/>
        </fileset>
    </path>

    <available file="${out}" property="outputExists"/>

    <target name="clean" description="remove all generated artifacts" if="outputExists">
        <delete dir="${out}" includeEmptyDirs="true"/>
        <delete dir="${reports.out}" includeEmptyDirs="true"/>
    </target>

    <target name="create" description="create the output directories" unless="outputExists">
        <mkdir dir="${production.classes}"/>
        <mkdir dir="${test.classes}"/>
        <mkdir dir="${reports.out}"/>
        <mkdir dir="${junit.out}"/>
        <mkdir dir="${testng.out}"/>
        <mkdir dir="${exploded.classes}"/>
        <mkdir dir="${exploded.lib}"/>
    </target>

    <target name="compile" description="compile all .java source files" depends="create">
        <!-- Debug output
                <property name="production.class.path" refid="production.class.path"/>
                <echo message="${production.class.path}"/>
        -->
        <javac srcdir="src" destdir="${out}/production/${ant.project.name}" debug="on" source="${version}">
            <classpath refid="production.class.path"/>
            <include name="**/*.java"/>
            <exclude name="**/*Test.java"/>
        </javac>
        <javac srcdir="${test.src}" destdir="${out}/test/${ant.project.name}" debug="on" source="${version}">
            <classpath refid="test.class.path"/>
            <include name="**/*Test.java"/>
        </javac>
    </target>

    <target name="junit-test" description="run all junit tests" depends="compile">
        <!-- Debug output
                <property name="test.class.path" refid="test.class.path"/>
                <echo message="${test.class.path}"/>
        -->
        <junit printsummary="yes" haltonfailure="${haltonfailure}">
            <classpath refid="test.class.path"/>
            <formatter type="xml"/>
            <batchtest fork="yes" todir="${junit.out}">
                <fileset dir="${test.src}">
                    <include name="**/*Test.java"/>
                </fileset>
            </batchtest>
        </junit>
        <junitreport todir="${junit.out}">
            <fileset dir="${junit.out}">
                <include name="TEST-*.xml"/>
            </fileset>
            <report todir="${junit.out}" format="frames"/>
        </junitreport>
    </target>

    <taskdef resource="testngtasks" classpathref="testng.class.path"/>
    <target name="testng-test" description="run all testng tests" depends="compile">
        <!-- Debug output
                <property name="test.class.path" refid="test.class.path"/>
                <echo message="${test.class.path}"/>
        -->
        <testng classpathref="test.class.path" outputDir="${testng.out}" haltOnFailure="${haltonfailure}" verbose="2" parallel="methods" threadcount="50">
            <classfileset dir="${out}/test/${ant.project.name}" includes="**/*.class"/>
        </testng>
    </target>

    <target name="exploded" description="create exploded deployment" depends="testng-test">
        <copy todir="${exploded.classes}">
            <fileset dir="${production.classes}"/>
        </copy>
        <copy todir="${exploded.lib}">
            <fileset dir="${production.lib}"/>
        </copy>
    </target>

    <target name="package" description="create package file" depends="exploded">
        <jar destfile="${out}/${ant.project.name}.jar" basedir="${production.classes}" includes="**/*.class"/>
    </target>

</project>