This section illustrates how to delegate to a CORBA server from a Web Service. In order to run this example you need an ORB such as the Novell exteNd Messaging Platform ORB installed on your system. In order to keep this section brief and to the point, we'll implement a very simple calculator service.
1 Calculator IDL Interface
The IDL interface for the calculator is shown below. It supports adding, subtracting, multiplying and dividing double precision numbers.
module corba
{
interface Calculator
{
| double add(in double x, in double y);
| double subtract(in double x, in double y);
| double multiply(in double x, in double y);
| double divide(in double x, in double y);
};
};
In order to generate CORBA stubs and skeletons for this interface, you need to run the idl2java compiler. This compiler is part of the ORB tools and you an look at the provided build file for an example of how to run it. Since the calculator is already in the 'corba' module, the generated classes will go into that Java package. The compiled .class files should be stored into the WEB-INF/classes directory as usual.
2 The Calculator CORBA Server
The implementation of the CORBA server is fairly straightforward: The server has a main method to bootstrap the server, and besides that an implementation of the four methods from the IDL interface.
package corba;
import java.io.FileOutputStream;
public class CorbaServer extends _CalculatorImplBase
{
public static void main(String[] args) throws Exception
{
| org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null);
| CorbaServer CS = new CorbaServer();
| FileOutputStream fos = new FileOutputStream("calc.ior");
| fos.write(orb.object_to_string(CS).getBytes());
| fos.flush();
| fos.close();
| System.out.println("CORBA calculator ready ...");
| orb.run();
}
public double add(double x, double y) {
| return x + y;
}
public double subtract(double x, double y) {
| return x - y;
}
public double multiply(double x, double y) {
| return x * y;
}
public double divide(double x, double y) {
| return x / y;
}
}
The main method store the IOR of the CORBA server into a file called 'calc.ior', which the Web Service can load as part of its initialization. The object reference for the CORBA server could also have been stored in a naming service.
3 Calculator RMI
In order to expose the above server as a Web Service, we need RMI for the calculator service. Since the interfaces generated by the IDL compiler are not proper RMI, we create a new interface, which is identical to the CORBA interface, but which extends java.rmi.Remote and where all methods throws java.rmi.RemoteException.
package corba;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface Calc extends Remote
{
double add(double x, double y) throws RemoteException;
double subtract(double x, double y) throws RemoteException;
double multiply(double x, double y) throws RemoteException;
double divide(double x, double y) throws RemoteException;
}
4 Calculator Web Service
At this point, we're back to using Novell exteNd WSSDK. We create a Web Service, which loads the 'calc.ior' file in its init method and delegates to the resulting CORBA object in the four business methods:
package corba;
import java.io.IOException;
import java.io.FileInputStream;
import javax.servlet.ServletException;
public class CalcImpl extends Calc_ServiceSkeleton
{
private Calculator calculator;
public void init() throws ServletException
{
| super.init();
|
| try {
| | String[] args = new String[0];
| | org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null);
| | FileInputStream fis = new FileInputStream("calc.ior");
| | byte[] b = new byte[fis.available()];
| | fis.read(b);
| | String ior = new String(b);
| | calculator = CalculatorHelper.narrow(orb.string_to_object(ior));
| | fis.close();
| } catch (IOException ex) {
| | throw new ServletException(ex.getMessage());
| }
}
public double add(double x, double y) {
| return calculator.add(x, y);
}
public double subtract(double x, double y) {
| return calculator.subtract(x, y);
}
public double multiply(double x, double y) {
| return calculator.multiply(x, y);
}
public double divide(double x, double y) {
| return calculator.divide(x, y);
}
}
In order to deploy the Web Service, you need to ensure that the ORB settings are correct. If the ORB is installed as a JDK extension, you can typically run without any additional settings. Please consult your ORB documentation for details.
5 Calculator Client
The client is similiar to any other client we have written in this tutorial. It creates a stub from the generated service and invokes each of the four business methods:
package corba;
import javax.xml.rpc.Stub;
import javax.naming.InitialContext;
public class Client
{
public static void main(String[] args) throws Exception
{
| // get the initial context
| InitialContext ctx = new InitialContext();
|
| // lookup the service for Hello
| CalcService svc = (CalcService)
| ctx.lookup("xmlrpc:soap:corba.CalcService");
|
| // get the hello stub
| Calc calc = (Calc) svc.getCalcPort();
|
| // set the end point address
| ((Stub)calc)._setProperty("javax.xml.rpc.service.endpoint.address",
| args.length > 0 ? args[0] :"http://localhost:9090/corba");
|
| System.out.println("2+3=" + calc.add(2,3));
| System.out.println("5-3=" + calc.subtract(5,3));
| System.out.println("2*3=" + calc.multiply(2,3));
| System.out.println("9/3=" + calc.divide(9,3));
}
}