Using RMI–IIOP in the Development of Distributed Applications Dr. P.G.Sarang, President &...

Using RMI–IIOP in the Using RMI–IIOP in the Development of Distributed Development of Distributed

ApplicationsApplicationsDr. P.G.Sarang, President & CEO, [email protected]

ABCOM Information Systems Private. Limited., Mumbai, India

Ms Nita P. Sarang, Consultant, [email protected]

CMC Limited, Mumbai, India

O'Reilly Conference on Java - Enterprise Java

Using RMI-IIOP in the Development of Distributed Applications

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RMIRMI

Remote Method InvocationSun’s programming model for

distributed objectsJava-based



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RMI – merits/demeritsRMI – merits/demerits

Advantages – Ease of programming – No complicated Interface Definition Language

(IDL) to learn

Disadvantages – Uses Proprietary Protocol

• Java Remote Method Protocol (JRMP)

– No cross-language support



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IIOPIIOP

Internet Inter-Operable ProtocolOMG’s programming model for

distributed objectsLanguage neutral



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IIOP – merits/demeritsIIOP – merits/demerits

Advantages– Interoperability

• Between different ORB vendors• Between different languages

Disadvantages– Need to learn Interface Definition Language

(IDL)– Complex Programming



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RMI/IIOP SuitabilityRMI/IIOP Suitability

A pure RMI Java solution is suitable for new developments

For legacy applications, a CORBA wrapper is required for protecting existing investments

How do we achieve How do we achieve best best

of both worlds?of both worlds?

RMI-IIOP Marriage



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ProposalProposal

A new protocol will confuse the userRMI-IIOP Merger should protect

investment in existing binariesReverse Mappings of RMI Interfaces

to CORBA IDLOMG is required to support Object

by Value (OBV)



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RequirementsRequirements

Existing RMI Clients and Servers both need upgrade to support IIOP



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RMI-IIOP ScenarioRMI-IIOP Scenario

RMI-IIOPClient

CORBAClient

CORBAServer

IIOP

IIOP

How do we convert How do we convert RMIRMI Application Application

to to RMI-IIOPRMI-IIOP Application? Application?



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Converting RMI to RMI-IIOPConverting RMI to RMI-IIOP

Use PortableRemoteObject class instead of UnicastRemoteObject

Use Java Naming & Directory Interface (JNDI) instead of RMIRegistry

Use narrow method instead of Java Casts



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ToolsTools

New rmic compiler– Converts Java Interfaces to IDL– Generates IIOP Stubs and tie classes

New idlj compiler– Maps IDL to Java– Generates IIOP Stubs and tie classes



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MigrationMigration

Converting existing RMI applications to RMI-IIOP applications.

Using Java-IDL to develop RMI-IIOP applications

Converting existing RMI Interfaces to CORBA IDL

Migration – Case 1

Existing RMI to RMI-IIOP



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RMI to RMI-IIOPRMI to RMI-IIOP

IIOP

RMI Java Client

RMI JavaServer

tie class

rmic -iiopComplier

stub class

RMIImplementation



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RMI to RMI-IIOPRMI to RMI-IIOP

1. Converting Server Extend your implementation class from

PortableRemoteObject rather than UnicastRemoteObject:

Use JNDI naming service rather than rmiregistry.

2. Converting Client Use JNDI naming service to locate object Use PortableRemoteObject.narrow() method

rather than Java type cast.



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Converting Server - Step 1Converting Server - Step 1

Use PortableRemoteObject rather than UnicastRemoteObject

import javax.rmi.PortableRemoteObject;…public class ComputeImpl extends

PortableRemoteObject implements Compute {

…}



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Converting Server - Step 2Converting Server - Step 2

Use JNDIimport javax.naming.*;…ReplaceNaming.rebind("//localhost/ComputeServer", obj);withjava.util.Properties env = System.getProperties();env.put ("java.naming.factory.initial",

"com.sun.jndi.cosnaming.CNCtxFactory");env.put ("java.naming.provider.url",

"iiop://localhost:900");Context ic = new InitialContext(env);ic.rebind ("//localhost/ComputeServer", obj);



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Converting Client - Step 1Converting Client - Step 1

Use JNDIReplace

Object obj = Naming.lookup ("ComputeServer");

With

java.util.Properties env = System.getProperties();

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

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

Context ic = new InitialContext(env);

Object obj = ic.lookup ("//localhost/ComputeServer");



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Converting Client - Step 2Converting Client - Step 2

Replace java typecast with a call to narrow methodReplace

Compute TaxObj = (Compute)obj;

With

Compute TaxObj = (Compute)PortableRemoteObject.narrow (obj, Compute.class);



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CompilingCompiling

Compile Java Source Filesjavac –d . *.java

Generate Stub and Tie Classesrmic –iiop <ImplClass>

Example:

rmic –iiop –d . com.abcom.tax.ComputeImpl



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Running – Step 1Running – Step 1

Use JNDI Name Server rather than rmiregistry

Start the JNDI Name Server with following command

start tnameserv (on Windows)

tnameserv & (on unix)



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Running – Step 2Running – Step 2

Start the Serverjava <RemoteServer>

Example:

java com.abcom.tax.ComputeImpl

Start the clientJava <RemoteClient>

Example:

java Client


IDL to RMI-IIOP



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StepsSteps

Write Java IDLUse idlj compiler – Generates Java Mappings– Generates stubs and skeletons

Implement ServerRun Server and register with JNDI

serviceDevelop Client and test



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ExampleExample

Sample Java IDLmodule abcom{

interface tax {

float CalculateTax(in float Amount);

};

};

idlj –fall sample.idl



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Generated FilesGenerated Files

Compiler generates following files in abcom Java package– _taxImplBase.java– _taxStub.java– tax.java– taxHelper.java– taxHolder.java– taxOperations.java


Existing

Java Interfaces to IDL



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RMI to IDLRMI to IDL

Use rmic to produce idlrmic –idl <ImplClass>

Map the generated idl to the desired language and provide implementation.



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RMI to IDLRMI to IDL

RMIInterface

Impl. class

rmic -idl IDL IDL to C++

C++ CORBAServer

rmic -iiop RMI-IIOPClient

IIOP



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Sample Java Remote InterfaceSample Java Remote Interface

package com.abcom.tax;

import java.rmi.Remote;import java.rmi.RemoteException;

public interface Compute extends Remote {float SalesTax (float Amount) throws RemoteException;

}



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Generated IDLGenerated IDL

#include "orb.idl"…module com {

module abcom {module tax { interface Compute { float SalesTax(in float arg0 );

};…};

};};



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LimitationsLimitations

RMI supports passing objects by value in both parameters and method return types

CORBA 2.3 specification now supports Object by Value (OBV)

CORBA inout, out parameters not supported



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OBV – Parameter ObjectsOBV – Parameter Objects

Examplepublic class Server extends PortableRemoteObject implements Compute {…public void printInvoice(Invoice inv)throws RemoteException {

…}

} rmic –idl Server



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Parameter Objects – Generated Parameter Objects – Generated FilesFiles

Following IDL files are generated– Compute.idl– Invoice.idl



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Parameter Objects – Parameter Objects – Compute.idlCompute.idl

valuetype Invoice;

…

interface Compute {

void printInvoice(in ::Invoice arg0 );

};



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Parameter Objects – Invoice.idlParameter Objects – Invoice.idl

valuetype Invoice { private long quantity;

private long totalAmt;

private ::CORBA::WStringValue itemDesc;

factory create( );

};



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OBV – Returning objectsOBV – Returning objects

Examplepublic class Server extends PortableRemoteObject implements Compute {…public Invoice computeInvoice()throws

RemoteException {…

}} rmic –idl Server



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Return Objects – Generated Return Objects – Generated FilesFiles

Following IDL files are generated.– Compute.idl– Invoice.idl



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Return Objects – Compute.idlReturn Objects – Compute.idl

valuetype Invoice;

…

interface Compute {

…

::Invoice computeInvoice( );

};

Invoice.idl is same as in previous case



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OBV – Dynamic DownloadingOBV – Dynamic Downloading

Remote classes for parameter objects can be dynamically downloaded using RMI class loading mechanism– Requires setting of java.rmi.server.codebase

environment variable



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Support for Objects by ValueSupport for Objects by Value

Supported in CORBA 2.3 specification

Initial support by Java IDL ORBSupport now added by Major ORB

vendorsSupport defined for Java and C++

ConclusionsConclusions

Thank YouThank You

Using RMI–IIOP in the Development of Distributed Applications Dr. P.G.Sarang, President &...

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