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XML-RPC – Examples

To demonstrate XML-RPC, we’re going to create a server that uses Java to process XML-RPC messages, and we will create a Java client to call procedures on that server.

The Java side of the conversation uses the Apache XML Project’s Apache XML-RPC, available at http://xml.apache.org/xmlrpc/

Put all the .jar files in appropriate path and let us create one client and one small XML-RPC server using JAVA.

XML-RPC Client

Let us write an XML-RPC client to call a function called sum function. This function takes two parameters and returns their sum.

import java.util.*;
import org.apache.xmlrpc.*;

public class JavaClient {
   public static void main (String [] args) {
   
      try {
         XmlRpcClient client = new XmlRpcClient("http://localhost/RPC2"); 
         Vector params = new Vector();
         
         params.addElement(new Integer(17));
         params.addElement(new Integer(13));

         Object result = server.execute("sample.sum", params);

         int sum = ((Integer) result).intValue();
         System.out.println("The sum is: "+ sum);

      } catch (Exception exception) {
         System.err.println("JavaClient: " + exception);
      }
   }
}

Let us see what has happened in the above example client.

  • The Java package org.apache.xmlrpc contains classes for XML-RPC Java clients and XML-RPC server, e.g., XmlRpcClient.
  • The package java.util is necessary for the Vector class.
  • The function server.execute(…) sends the request to the server. The procedure sum(17,13) is called on the server as if it were a local procedure. The return value of a procedure call is always an Object.
  • Here “sample” denotes a handler that is defined in the server.
  • Note that all the parameters of the procedure call are always collected in a Vector.
  • The XmlRpcClient class is constructed by specifying the “web address” of the server machine followed by /RPC2.
    • localhost – means the local machine
    • You can specify an IP number instead of localhost, e.g. 194.80.215.219
    • You can specify a domain name like xyz.dyndns.org
    • You can specify a port number along with domain name as xyz.dyndns.org:8080. The default port is 80
  • Note that the result of the remote procedure call is always an Object and it has to be casted to the appropriate type.
  • When problems occur (no connection, etc.), an Exception is thrown and it has to be caught using catch statement.

Due to the above call, a client sends the following message to the server. Note that this is handled by server.execute(…) internally and you have nothing to do with it.

<?xml version="1.0" encoding="ISO-8859-1"?>
<methodCall>
   <methodName>sample.sum</methodName>
   <params>
      <param>
         <value><int>17</int></value>
      </param>
		 
      <param>
         <value><int>13</int></value>
      </param>
   </params>
</methodCall>

XML-RPC Server

Following is the source code of XML-RPC Server written in Java. It makes use of built-in classes available in org.apache.xmlrpc.*

import org.apache.xmlrpc.*;

public class JavaServer { 

   public Integer sum(int x, int y){
      return new Integer(x+y);
   }

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

         System.out.println("Attempting to start XML-RPC Server...");
         
         WebServer server = new WebServer(80);
         server.addHandler("sample", new JavaServer());
         server.start();
         
         System.out.println("Started successfully.");
         System.out.println("Accepting requests. (Halt program to stop.)");
         
      } catch (Exception exception){
         System.err.println("JavaServer: " + exception);
      }
   }
}

Let us see what we have done in the above example server.

  • The package org.apache.xmlrpc contains the class WebServer for a XML-RPC Server implementation.
  • The procedure sum that is called remotely is implemented as a public method in a class.
  • An instance of the same server class is then associated with a handler that is accessible by the client.
  • The server is initialized by the port number (here: 80).
  • When problems occur, an Exception is thrown and has to be caught using the catch statement.

For the call mentioned in the given example client, the server sends the following response back to the client:

<?xml version="1.0" encoding="ISO-8859-1"?>
<methodResponse>
   <params>
      <param>
         <value><int>30</int></value>
      </param>
   </params>
</methodResponse>

Now your server is ready, so compile and run it at your prompt as follows:

C:\ora\xmlrpc\java>java JavaServer
Attempting to start XML-RPC Server...
Started successfully.
Accepting requests. (Halt program to stop.)

Now to test the functionality, give a call to this server as follows:

C:\ora\xmlrpc\java>java JavaClient
30

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