import java.net.URL;
import java.net.URLClassLoader;

public class ClassLoaderTest {

    public static void main(String[] args) throws Exception {
        URL[] url = { new URL("file:D:/ant/gao-util/dest/gao-jpa.jar") };
        URLClassLoader classloader = new URLClassLoader(url);        
        Class<?> clazz = classloader.loadClass("net.blogjava.frankiegao123.jpa.query.DateQuery");
        Object dateQuery = clazz.newInstance();
        System.out.println(dateQuery);
    }
}

------解决方案--------------------
Java code

    public static void main(String[] args) {
        try {

            URL url = new URL("file:///D:/workspace/test/bin/test.jar");

            URLClassLoader urlCL = new URLClassLoader(new URL[] { url });

            Class c = urlCL.loadClass("TestClassA");

            Method m = c.getMethod("method");
            
            m.invoke(c.newInstance(), null);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }