Apache Ant java.lang.NoClassDefFoundError

I am new in Ant , I am doing a program client-server with Eclipse , I am using external libraries: JMapViewer-1.14.1.jar , the server works correctly the client sends me an error.

When executing from the Ubuntu terminal:

ant clean compile jar run

I receive a error in the target run :

     [java] Error: A JNI error has occurred, please check your installation and try again
     [java] Exception in thread "main" java.lang.NoClassDefFoundError: org/openstreetmap/gui/jmapviewer/JMapViewer
     [java]     at java.lang.Class.getDeclaredMethods0(Native Method)
     [java]     at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
     [java]     at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
     [java]     at java.lang.Class.getMethod0(Class.java:3018)
     [java]     at java.lang.Class.getMethod(Class.java:1784)
     [java]     at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
     [java]     at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
     [java] Caused by: java.lang.ClassNotFoundException: org.openstreetmap.gui.jmapviewer.JMapViewer
     [java]     at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
     [java]     at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
     [java]     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
     [java]     at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
     [java]     ... 7 more
     [java] Java Result: 1

My file build.xml:

<project>

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

    <target name="compile">
        <mkdir dir="build/classes" />
        <javac includeantruntime="false" srcdir="src" destdir="build/classes">
            <classpath>
                <pathelement path="/home/bryan/Scrivania/Libraries/JMapViewer-1.14.1.jar" />
                <pathelement path="/home/bryan/Scrivania/Libraries/mail.jar" />
                <pathelement path="/home/bryan/Scrivania/Libraries/postgresql-42.0.0.jre6.jar" />
            </classpath>

        </javac>
    </target>

    <target name="jar">

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

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

</project>