This page describes some advanced topics.

Dynamic proxies

Dynamic proxies are an extremely comfortable way of Client programming. Basically, the idea is as follows: All request processors on the server side are splitted into interface and implementation. The interfaces are shared between client and server, typically within some common jar file. Now, rather than using the XmlRpcClient directly, the programmer creates an instance of ClientFactory, which is configured with an XmlRpcClient.

The factory can take an interface as input and returns an implementation, which internally calls the server by using the XmlRpcClient.

Perhaps some code shows more than words. First of all, let's create a request processor interface.

    package com.foo;

    public interface Adder {
      public int add(int pNum1, int pNum2);
    }

The server contains the request processors implementation:

    package com.foo;

    public class AdderImpl implements Adder {
      public int add(int pNum1, int pNum2) {
        return pNum1 + pNum2;
      }
    }

And here is how the client would use this:

    import com.foo.Adder;
    import org.apache.xmlrpc.client.XmlRpcClient;
    import org.apache.xmlrpc.client.XmlRpcClientConfigImpl;
    import org.apache.xmlrpc.client.util.ClientFactory;

    XmlRpcClientConfigImpl config = new XmlRpcClientConfigImpl();
    config.setServerUrl("http://127.0.0.1:8080/xmlrpc");
    XmlRpcClient client = new XmlRpcClient();
    client.setConfig(config);
    ClientFactory factory = new ClientFactory(client);
    Adder adder = (Adder) factory.newInstance(Adder.class);
    int sum = adder.add(2, 4);

Exception handling

Currently, exceptions are a problem: If the server throws an exception (for example an IOException), then the client receives an XmlRpcException. Consequently, the generated implementation will attempt to throw the XmlRpcException.

Unfortunately, the method signature will of course contain an IOException, but rarely an XmlRpcException. As the XmlRpcException cannot be thrown, it is converted into an UndeclaredThrowableException.

This is no problem, if you are prepared for runtime exceptions by enclosing your code with proper exception handlers. (Of course, the exception handlers may be in a calling method.) Only if you want to catch the exception (for example, because you expect an error at a certain point), then you need to consider, which exception is being trapped: If the method exposes XmlRpcException, then you'll need to catch the XmlRpcException. Otherwise, it's UndeclaredThrowableException.

Custom data types

Apache XML-RPC was built with extensibility in mind. In particular, it was written to support custom data types.

The data type handling is completely left to the TypeFactory. In other words, adding support for custom data types is as simple as providing your own type factory. This is typically done by subclassing TypeFactoryImpl.

We'll illustrate the concept by creating a type factory, which uses a non-standard date format for transmitting date values. First of all, we've got to implement the subclass:

    import java.text.DateFormat;
    import java.text.SimpleDateFormat;
    import org.apache.xmlrpc.common.TypeFactoryImpl;
    import org.apache.xmlrpc.common.XmlRpcController;
    import org.apache.xmlrpc.parser.DateParser;
    import org.apache.xmlrpc.parser.TypeParser;
    import org.apache.xmlrpc.serializer.DateSerializer;
    import org.apache.xmlrpc.serializer.TypeSerializer;
    import org.apache.ws.commons.util.NamespaceContextImpl;

    public class MyTypeFactory extends TypeFactoryImpl {
        public MyTypeFactory(XmlRpcController pController) {
            super(pController);
        }

        private DateFormat newFormat() {
            return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
        }

        public TypeParser getParser(XmlRpcStreamConfig pConfig, NamespaceContextImpl pContext, String pURI, String pLocalName) {
            if (DateSerializer.DATE_TAG.equals(pLocalName)) {
                return new DateParser(pFormat);
            } else {
                return super.getParser(pConfig, pContext, pURI, pLocalName);
            }
        }

        public TypeSerializer getSerializer(XmlRpcStreamConfig pConfig, Object pObject) throws SAXException {
            if (pObject instanceof Date) {
                return new DateSerializer(newFormat());
            } else {
                return super.getSerializer(pConfig, pObject);
            }
        }
    }

On the client side, we've got to tell the XmlRpcClient to use the new factory. That's as simple as typing

    XmlRpcClient client = new XmlRpcClient();
    client.setTypeFactory(new MyTypeFactory());

Things are a little bit more difficult on the server side. Basically all we need to do is setting the type factory on the XmlRpcServer. The question is, how to obtain the server object. That depends on the environment. If you are using the XmlRpcServlet, then you've got to derive a subclass:

    import org.apache.xmlrpc.webserver.XmlRpcServletServer;
    import org.apache.xmlrpc.webserver.XmlRpcServlet;

    public class MyXmlRpcServlet extends XmlRpcServlet {
        protected XmlRpcServletServer newXmlRpcServer(ServletConfig pConfig) {
            XmlRpcServletServer server = super.newXmlRpcServer(pConfig);
            server.setTypeFactory(new MyTypeFactory(server));
            return server;
        }
    }

And, if you are using the WebServer, you've got to override a similar method:

    import java.net.InetAddress;
    import org.apache.xmlrpc.server.XmlRpcStreamServer;
    import org.apache.xmlrpc.webserver.WebServer;
    
    public class MyWebServer extends WebServer {
        public MyWebServer(int pPort) {
            super(pPort);
        }

        public MyWebServer(int pPort, InetAddress pAddr) {
            super(pPort, pAddr);
        }

            protected XmlRpcStreamServer newXmlRpcStreamServer() {
                XmlRpcStreamServer server = new ConnectionServer();
                server.setTypeFactory(new MyTypeFactory());
                return server;
            }
        }