带有.jar lib的Java ant build.xml编译得很好，但执行失败

Question

我是一个学习创建ant构建文件的学生，我在/ src中有一些.java源文件，在/ lib中有一个.jar库（json.jar）。我已经在build.xml中的javac的类路径中包含了.jar，它编译得很好，但是在执行时失败了：

     [echo] command line execute: java -cp classes:lib/json.jar Main
 [java] Exception in thread "main" java.lang.NoClassDefFoundError: org/json/JSONString
 [java]     at java.base/java.lang.ClassLoader.defineClass1(Native Method)
 [java]     at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1007)
 [java]     at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174)
 [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:801)
 [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:699)
 [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:622)
 [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:580)
 [java]     at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
 [java]     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
 [java]     at Main.main(Unknown Source)
 [java] Caused by: java.lang.ClassNotFoundException: org.json.JSONString
 [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
 [java]     at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
 [java]     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
 [java]     ... 10 more
 [java] Java Result: 1

这是我的build.xml：

<?xml version="1.0"?>
<project name="Ant-Test" default="targets" basedir=".">
    <!-- Sets variables which can later be used. -->
    <!-- The value of a property is accessed via ${} -->
    <property name="src.dir" location="src" />
    <property name="build" location="classes" />
    <property environment="env"/>
    <property name="lib" value="lib" />
    <property name="user" value="${env.USERNAME}"/>

    <path id="compile.classpath">
        <pathelement location="${build}"/>
        <pathelement path="lib/json.jar"/>
    </path>

    <target name="targets">
        <echo message="Targets are clean, prepare, build, execute, and targets"/>
    </target>

    <path id="compile.classpath">
        <pathelement location="${build}"/>
    </path>

    <!-- Deletes the existing build, docs and dist directory-->
    <target name="clean">
        <delete dir="${build}" />
    </target>

    <!-- Creates the  build, docs and dist directory-->
    <target name="prepare">
        <mkdir dir="${build}" />
    </target>

    <!-- Compiles the java code (including the usage of library for JUnit -->
    <target name="build" depends="prepare">
        <javac srcdir="${src.dir}" includeantruntime="false" destdir="${build}" classpath="lib/json.jar">
            <classpath refid="compile.classpath"/>
        </javac>
    </target>

    <target name="execute" depends="build" description="Run the program">
        <echo message="command line execute: java -cp classes:lib/json.jar Main" />
        <java classname="Main" fork="yes">
            <classpath refid="compile.classpath"/>
        </java>
    </target>
</project>

我不确定还有什么可以尝试，感谢任何帮助！