The Ancient Art of Programming

Gary Blomquist asked me to share the Spring ServiceExporter mentioned in the previous post. Here is is:

package jteam.remoting.xmlrpc;
 
import java.io.OutputStream;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.apache.xmlrpc.XmlRpcServer;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.remoting.support.RemoteExporter;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;
import org.springframework.web.servlet.support.WebContentGenerator;
 
/**
 * Web controller that exports the specified service bean as XML-RPC service
 * endpoint, accessible via a XML-RPC proxy.
 *
 * XML-RPC is a simple, SOAP-like protocol. For more information, see the
 * XML-RPC website.
 *
 * @author Arjen Poutsma
 */
public class XmlRpcServiceExporter
  extends RemoteExporter 
  implements Controller, InitializingBean {
    private XmlRpcServer server;
 
    public void afterPropertiesSet()
  throws Exception {
        server = new XmlRpcServer();
        server.addHandler(getServiceInterface().getName(), getProxyForService());
    }
 
    /**
     * Process the incoming XML-RPC request and create a XML-RPC response.
     *
     * @param request current HTTP request
     * @param response current HTTP response
     * @return null
     * @throws Exception in case of errors.
     */
    public ModelAndView handleRequest(HttpServletRequest request, 
                                      HttpServletResponse response)
    throws Exception {
        if (!WebContentGenerator.METHOD_POST.equals(request.getMethod())) {
            throw new ServletException(“XmlRpcServiceExporter only supports ” +
              “POST requests”);
        }
        byte[] result = server.execute(request.getInputStream());
        response.setContentType(“text/xml”);
        response.setContentLength(result.length);
        OutputStream output = response.getOutputStream();
        output.write(result);
        output.flush();
 
        return null;
    }
 
}

Nothing fancy. The full name of the service interface is used as a handler name. So if your interface is called jteam.businesslogic.TestManager, it gets exposed as jteam.businesslogic.TestManager.

This class depends on the Apache XML-RPC library to do the actual XML-RPC handling. This library does have it’s weaknesses: it uses the old, synchronized collections (Vector and Hashtable), and it does not handle XML-RPC structs very well, since it converts a struct into a Hashtable with the string names mapped to the value.

I would have preferred a more XStream-like approach, where the following struct:

<struct>
   <member>
      <name>lowerBound</name>
      <value><i4>18</i4></value>
   </member>
   <member>
      <name>upperBound</name>
      <value><i4>139</i4></value>
   </member>
</struct>

would have been converted into a bean with lowerBound and upperBound properties. If it bothers me too much, I will add this functionality myself.