Creating an XML-RPC Server

Now that you have a Java class that will handle XML-RPC requests, you're ready to develop a server that waits for these requests to arrive, dispatching them to the handler.

The LottoServer class drives a simple web server that looks for these requests.

Apache XML-RPC has two core packages: org.apache.xmlrpc for applications and org.apache.xmlrpc for applications.

The WebServer class in org.apache.xmlrpc functions as a bare-bones XML-RPC server that listens on a specified TCP/IP Internet port:

int port = 4404;

server = new WebServer(port);

The choice of port number 4404 is arbitrary; any port from 1,024 through 49,151 could be chosen.

By the way The Internet Assigned Numbers Authority, a group that decrees how ports below 1,024 are used, offers a directory of port numbers and the software using them on the Web: http://www.iana.org/assignments/port-numbers.

The server's addHandler() method designates a class that will handle XML-RPC requests:

LottoCounter counter = new LottoCounter();

server.addHandler("lotto", counter);

The method's arguments are an identifier that gives the handler a name and an object. The LottoCounter object counter has been assigned the name "lotto", so the public methods of that object may be called over XML-RPC.

There's one such method, sendRequest(), which will be called over XML-RPC as lotto.sendRequest. No parentheses should follow the method name—they are omitted in XML-RPC.

An XML-RPC server can add as many handlers as desired, which don't need to belong to the same class.

The server can be launched by calling its start() method:

server.start();

Enter the text of Listing 25.3 and save the file under the name LottoServer.java.

Listing 25.3. The Full Text of LottoServer.java

 1: import java.io.*;

 2: import nu.xom.*;

 3: import org.apache.xmlrpc.*;

 4:

 5: public class LottoServer {

 6:     int port = 4404;

 7:     WebServer server;

 8:

 9:     public LottoServer() throws IOException, ParsingException {

10:         // create the server

11:         System.out.println("Creating server on port " + port);

12:         server = new WebServer(port);

13:

14:         // register the request handler

15:         LottoCounter counter = new LottoCounter();

16:         server.addHandler("lotto", counter);

17:     }

18:

19:     public void start() {

20:         // start the server

21:         System.out.println("Now accepting requests");

22:         server.start();

23:     }

24:

25:     public static void main(String[] arguments) {

26:         try {

27:             LottoServer lotto = new LottoServer();

28:             lotto.start();

29:         } catch (Exception exception) {

30:             System.out.println("Error: " + exception.getMessage());

31:         }

32:     }

33: }

Compile and run the application, which requires no command-line arguments:

java LottoServer

The following output indicates the server's running and ready to receive requests:

Creating server on port 4404

Now accepting requests

On a Windows system, you must leave this running and open a second command-line window to create the XML-RPC client. On Linux, you can start the server in the background by putting an "&" character after the command:

java LottoServer &

When running the application in the background, to stop it later on, you must use the ps command to find its process ID, then the kill command to bring it to a halt.

Here's an example for the Bash shell on Linux:

ps auxw | grep LottoServer



rcade    10424  0.0  1.3 269764 14320 pts/0  S    Jul13   0:00 /usr/java/jdk1.5.0/bin/java

 LottoServer



kill -9 10424