我正在用Java编写学校的项目（离散模拟库），当我运行示例应用程序时，我仍然收到此错误：
[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$1.run(URLClassLoader.java:202)
...
[java] at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
[java] Could not find the main class: /home/lut/Plocha/IMS/examples/Random/random.RandomTest. Program will exit.
[java] Java Result: 1
（/ home / lut / Plocha / IMS是根目录。在这里的文件树中，它标记为.-- dot）
我在根目录中有库。还有目录examples，其中使用此库的示例应用程序很小，每个应用程序都有自己的构建ant脚本。
目录结构：
.
├── build.xml <-- library build-file, examples are not included in this build
├── doc
├── examples
│ ├── Random
│ │ ├── build.xml <-- example app buil-file
│ │ └── src
│ │ └── random
│ │ └── RandomTest.java <-- main class of the example
│ └── Calendar
│ ├── build.xml, src, etc. inside
│ ...
├── dest <-- after library build, dsim.jar is here
├── build
└── src <-- source files of the library
└── ims
├── Distribution
│ └── RandomGenerator.java
├── Exception
│ ├── RandomException.java
│ └── SimulationException.java
└── SimObjects
├── Entity.java
├── Event.java
├── Facility.java
...
我可以构建两个主库（dsim.jar文件夹中的输出为./dest）和示例应用程序（在./examples/Random中）而没有问题，但是当我尝试运行该示例时应用（ant run），我仍然会收到NoClassDefFoundError。
示例应用的build.xml（在./examples/Random中）如下所示：
<?xml version="1.0" encoding="UTF-8"?>
<project name="Example - Random generator" default="compile" basedir=".">
<property name="src" location="src"/>
<property name="build" location="build"/>
<property name="dest" location="dest"/>
<property name="dsim.dir" location="../../dest"/>
<property name="dest.jar" location="${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="${dest.jar}" fork="true" classpathref="dsim-classpath"/>
</target>
</project>
RandomTest.java文件以行开头：
package random;
import ims.Distribution.RandomGenerator;
import ims.Exception.SimulationException;
import ims.SimObjects.Histogram;
public class RandomTest {
public static void main(String[] args) throws SimulationException {
我尝试在谷歌搜索，有几篇关于类路径的帖子及其问题，但即使我无法确定哪里可能有问题。我究竟做错了什么？我错过了什么？
非常感谢。
答案 0 :(得分：2)
班级名称为random.RandomTest。
这是什么？
.home.lut.Plocha.IMS.examples.Random.random.RandomTest
为什么类加载器正在寻找这个？
这是一个适用于我的通用build.xml。创建目录结构，看看它是否排序：
<?xml version="1.0" encoding="UTF-8"?>
<project name="xslt-converter" basedir="." default="package">
<property name="version" value="1.6"/>
<property name="haltonfailure" value="no"/>
<property name="out" value="out"/>
<property name="production.src" value="src"/>
<property name="production.lib" value="lib"/>
<property name="production.resources" value="config"/>
<property name="production.classes" value="${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>
答案 1 :(得分：1)
好的，所以问题是错误的属性属性名称（我在main-class属性定义中有位置而不是值）。
<property name="main-class" location="random.RandomTest"/>
<!-- shoudl be -->
<property name="main-class" value="random.RandomTest"/>
然后loader找到主类，但出现了另一个问题：loader无法找到库类（./src/中的类）
[java] java.lang.NoClassDefFoundError: ims/Exception/SimulationException
[java] Caused by: java.lang.ClassNotFoundException: ims.Exception.SimulationException
但为什么呢？有类路径引用。或者是jar和classpath属性的排他性问题（frist @ duffymo的答案下的评论）？如何修复我的build.xml以使其工作？ 感谢。