J2EE Tutorial - Running RMI Example

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J2EE Tutorial - Running RMI Example

greeter.java

import java.rmi.*;

public interface greeter extends Remote

{

String greetme(String s) throws RemoteException;

}

greeterimpl.java

import javax.rmi.PortableRemoteObject;

import javax.naming.*;

import java.rmi.*;

import java.rmi.server.*;

import greeter.*;

public class greeterimpl extends

PortableRemoteObject implements greeter

{

String s;

public static void main(String args[])

{

try

{

Context initialNamingContext = new InitialContext();

// System.setSecurityManager(new RMISecurityManager());

greeterimpl obj = new greeterimpl("sam");

initialNamingContext.rebind("sam",obj);

System.out.println("remote server ready!");

System.out.println("sam is registered & waiting for call");

}

catch(Exception e1)

{

System.out.println("error"+e1);

}

public greeterimpl(String a) throws RemoteException

{

s = " SUN'S RMI-IIOP(RMI-CORBA) PROGRAM WELCOMES .........";

}

public String greetme(String a) throws RemoteException

{

return s+ a;

}

greeterclientservlet.java

import javax.servlet.*;

import java.io.*;

import javax.servlet.http.*;

import greeter.*;

import greeterimpl.*;

import _greeterimpl_Tie.*;

import java.rmi.*;

import java.rmi.server.*;

import javax.rmi.PortableRemoteObject;

import javax.naming.*;

import java.util.*;

public class greeterclientservlet extends HttpServlet

{

public void doPost(HttpServletRequest request,

HttpServletResponse response) throws

ServletException,IOException

{

response.setContentType("text/html");

PrintWriter out=response.getWriter();

try

{

String s1=request.getParameter("text1");

Hashtable hash1 = new Hashtable();

hash1.put("java.naming.factory.initial","com.sun.jndi.cosnaming.CNCtxFactory");

hash1.put("java.naming.provider.url","iiop://localhost:900");

Context context1 = new InitialContext(hash1);

greeter obj=

(greeter)PortableRemoteObject.narrow(context1.lookup("sam"),greeter.class);

String s = obj.greetme(s1);

out.println("<html>");

out.println("<body>");

out.println(s);

out.println("</body>");

out.println("</html>");

}

catch(Exception e1) { out.println("error"+e1); }

}

greeterclientservlet.htm

<html>

<body>

ENTER NAME <input type=text name="text1" size=20>

<br>

</form>

</body>

</html>

How to compile and run the RMI-IIOP program?

1) We require jndi package for running this program.

We create a folder in c:\jdk1.3\bin\rmicorba.

2) We brought jndi folder into c:\jdk1.3\bin\rmicorba.

3) cd to c:\jdk1.3\bin\rmicorba.

4) set path=c:\windows;c:\windows\command;c:\jdk1.3\bin;

5) set classpath=c:\jdk1.3\bin\rmicorba

6) create greeter.java in this folder.

7) compile greeter.java

8) create and compile greeterimpl.java

9) MOST IMPORTANT STEP.

>rmic -iiop greeterimpl

(creates corba style stub and tie class files.)

10) start tnameserv // ( this is transient name server)

>tnameserv

11) Go to another window ,set path & classpath as before.

start the server and register the remote object. (this line must be typed most carefully without break!) (continuously).

>java -Djava.naming.factory.initial=com.sun.jndi.cosnaming.CNCtxFactory

-Djava.naming.provider.url=iiop://localhost helloimpl

( -Djava means we are supplying runtime properties)

12) If every thing is done correctly , you will find the following

message in the console.

'remote server ready!'

'sam is registered and waiting for call'

13) Now compile greeterclientservlet.java

We have to set classpath=%classpath%;c:\jsdk2.0\src

14) After compiling copy all the classfiles in c:\jdk1.3\bin\rmicorba folder to

c:\tomcat\webapps\root\web-inf\classes folder

15) copy greeterclientservlet.htm to c:\tomcat\webapps\root directory.

16) Start the tomcat server as already seen.

17) type the URL as 'http://localhost:8080/greeterclientservlet.htm"

in the browser.

18) We get the form. Type your name ( say 'Thomas') and submit.

19) We will get the greeting :

" SUN'S RMI-IIOP(RMI-CORBA) PROGRAM WELCOMES ...Thomas"

20) Thus we have invoked the remote object's method in Corba style.

21) So far so good. But how about the automatic generation of IDL for non-java end? This is the best part of RMI--IIOP,

See step 9 listed above. We used the -iiop flag while invoking rmic compiler.

If we use -idl flag instead, we get the idl file automatically generated.

We can then distribute this idl file to other corba customers.

You would have noticed that , we have changed the order in which distributed order technologies in the j2ee basket were mentioned. Instaed of taking up JAVA-IDL after RMI, we took up RMI-IIOP. This way, we can easily compare RMI & RMI-IIOP.

Just to complete the picture, we will now see the JAVA-IDL version of the same program and then on to the meat of J2EE (IE) EJB.

There are 4 files as follows:

1) greeter.idl

2) greeterserver.java

3) greeterservlet.java

4) greeterservlet.htm

We begin with greeter.idl , which is the interface file written in OMG-IDL.

Let us edit this file in say, c:\idl folder.

Set path for the dos window

c:\idl>set path=c:\windows\command;c:\jdk1.3\bin

Also set classpath:

c:\idl>set classpath=c:\idl

Create greeter.idl as given below.

greeter.idl

interface greeter

{

string greetme(in string s);

};

We now use the idl compiler in jdk1.3 as follows:

c:\idl>idlj -fall greeter.idl

This command creates a number of java source files as follows:

1) greeter.java

2) _greeterImplBase.java

3) _greeterStub.java

4) greeterHelper.java

5) greeterHolder.java

6) greeterOperations.java

These files are created in the same folder as greeter.idl because we have not specified 'module' in the idl file. This is a simple method.

Now, create greeterserver.java in the same folder as follows:

greeterserver.java

import org.omg.CORBA.*;

import org.omg.CosNaming.*;

import java.io.*;

public class greeterserver

{

public static void main(String[] args)

{

try

{

ORB orb = ORB.init(args,null);

greeterservant ref = new greeterservant();

orb.connect(ref);

org.omg.CORBA.Object objRef =orb.resolve_initial_references("NameService");

NamingContext ncRef = NamingContextHelper.narrow(objRef);

NameComponent nc = new NameComponent("greeter","");

NameComponent path[] = {nc};

ncRef.rebind(path,ref);

System.out.println("server ready...waiting for client");

java.lang.Object sync = new java.lang.Object();

synchronized(sync)

{

sync.wait();

}

catch(Exception e1)

{

System.out.println(" "+e1);

}

}//main

}//class

//-------------

class greeterservant extends _greeterImplBase

{

public String greetme(String s)

{

return "How are you....?"+s;

}

Compile all the java files as follows:

c:\idl>javac *.java

This compiles all the java files in the folder.

We now create the servlet file which is the client for the corba program.

greeterservlet.java

import org.omg.CORBA.*;

import org.omg.CosNaming.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

import java.util.*;

public class greeterservlet extends HttpServlet

{

greeter server;

public void init(ServletConfig config) throws ServletException

{

super.init(config);

try

{

ORB orb = ORB.init((String[])null,null);

org.omg.CORBA.Object objRef =

orb.resolve_initial_references("NameService");

NamingContext ncRef = NamingContextHelper.narrow(objRef);

NameComponent nc = new NameComponent("greeter","");

NameComponent path[] = {nc};

server = greeterHelper.narrow(ncRef.resolve(path));

System.out.println("servlet init ok!");

} catch(Exception e1){System.out.println(""+e1);}

} //init

public void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException

{

response.setContentType("text/html");

PrintWriter out=response.getWriter();

String a =request.getParameter("text1"); // name

System.out.println(a);

String s1=server.greetme(a);

out.println(s1);

}

} //--servlet over-----

To compile the servlet file, we should set classpath as follows:

c:\idl>set classpath=%classpath%;c:\jsdk2.0\src;

c:\idl>javac greeterservlet.java

This command compiles the servlet.

The following html file invokes the servlet.

<html>

<body>

</form>

</body>

</html>

Now, we copy greeterservlet.htm to c:\tomcat\webapps\root

Then we copy all the class files in c:\idl folder to:

c:\tomcat\webapps\root\web-inf\classes folder.

We are now ready to test our corba program.

Start Tomcat as before.

Start the browser and type the URL as:

"http://localhost:8080/greeterservlet.htm"

We get a form with a textbox. Fill up your name,say Thomas and

submit.

We will get :

"How are you...?Thomas".

We have completed the first leg of our long journey.

In the second part, we will take up EJB , XML etc. In the previous instalment , we familiarized ourselves with Servlet, JSP, JavaMail, JDBC, RMI, RMI-IIOP and IDL. as, these were preliminaries to grapple with EJB. Now , it is time to takeup EJB.

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