URLClassLoader

This example shows how a service implementation can be loaded with a URLClassLoader.

    The files.
        HelloService.java:

        public interface HelloService {
            public void sayHello();
        }


        HelloServiceImpl.java:

        public class HelloServiceImpl implements HelloService {
            @Override
            public void sayHello() {
        	System.out.println("Hello!");
            }
        }


        ServiceFactory.java uses URLClassLoader to load the service implementation:

        import java.io.*;
        import java.net.*;

        public class ServiceFactory {
            private static URL[] classLoaderUrls;

            public static void setURLs(URL[] urls) {
        	classLoaderUrls = urls;
            }

            public static HelloService getHelloService() throws Exception {
        	URLClassLoader loader = new URLClassLoader(classLoaderUrls);
        	return (HelloService) Class.forName("HelloServiceImpl", true, loader).newInstance();
            }
        }


        Test.java:

        import java.io.*;
        import java.net.*;

        public class Test {
            public static void main(String[] args) throws Exception {
        	ServiceFactory.setURLs(new URL[] { 
        	    new URL("file:service.jar")
        	});

        	HelloService h = ServiceFactory.getHelloService();
        	System.out.println("Class Loader: " + h.getClass().getClassLoader());
        	h.sayHello();
            }
        }



    Create a runnable client jar:

    C:\>jar -cfe client.jar Test Test.class ServiceFactory.class HelloService.class


    Create a service jar:

    jar -cf service.jar HelloServiceImpl.class


    Test:

    C:\>java -jar client.jar
    Class Loader: java.net.URLClassLoader@addbf1
    Hello!