java.lang.NoClassDefFoundError in Ant

Question

I faced with the problem, when I am creating build.xml in Ant. The jar file is created, but at run stage throws this error:

     [java] Exception in thread "main" java.lang.NoClassDefFoundError: org/springframework/boot/SpringApplication
     [java]     at com.example.DemoApplication.main(Unknown Source)
     [java] Caused by: java.lang.ClassNotFoundException: org.springframework.boot.SpringApplication
     [java]     at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
     [java]     at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
     [java]     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
     [java]     ... 1 more
     [java] Java Result: 1

This is my build.xml file:

    <path id="classpath">
        <fileset dir="lib" includes="**/*.jar" />
    </path>

    <target name="clean">
        <delete dir="build"/>
        <delete dir="lib"/>
    </target>

    <target name="compile">
        <mkdir dir="build/classes"/>
        <javac srcdir="src" destdir="build/classes" classpathref="classpath"/>
    </target>

    <target name="jar">
        <mkdir dir="build/jar"/>
        <jar destfile="build/jar/HelloWorld.jar" basedir="build/classes">
            <manifest>
                <attribute name="Main-Class" value="com.example.DemoApplication"/>
            </manifest>
        </jar>
    </target>

    <target name="run" depends="jar">
        <java jar="build/jar/HelloWorld.jar" fork="true" />
    </target>

    <target name="all" depends="clean,resolve, compile, jar, run"/>

    <target name="resolve">
        <ivy:retrieve />
    </target>

</project>

How could this problem be solved?