Programming in Java

交通大學資訊工程學系

Programming in Java

RMI

蔡文能交通大學資訊工程學系[email protected]

http://www.csie.nctu.edu.tw/~tsaiwn/java/

交通大學資訊工程學系蔡文能 RMI-第 2頁

Java RMI

AgendaRMI IntroductionRPC vs. RMI Remote Procedure Call Remote Method invocation

RPC exampleRMI Architecture Client stub and Server skeleton RMI Deployment and RMI registry RMI Example

From function to Distributed computing DLL, RPC/RMI, CORBA, Web Services


Java RMI


Java RMI


Java RMI

RMI Introduction RMI enables the programmer to create distributed Java

applications, in which the methods of remote Java objects can be invoked from other Java virtual machines, possibly on different hosts.

A Java program can make a call on a remote object once it obtains a reference to the remote object, either by looking up the remote object in the naming service provided by RMI or by receiving the reference as an argument or a return value. A client can call a remote object in a server, and that server can also be a client of other remote objects.

RMI uses object serialization to marshal and unmarshal parameters.


Java RMI

Serialization

Action of encoding of an object into a stream of bytes

RMI performs marshalling/unmarshalling via Java Serialization Marshalling is the process of encoding arguments and results for

transmission

Thus, objects to be marshalled or unmarshalled must be serializable ( should implements java.io.serializable)


Java RMI

RMI Overview

Remote Method Invocation Java version of RPC

ha.nctu.edu.tw hehe.nctu.edu.tw

networknetworkObjectClient

RemoteObjectServer

method invocation


Java RMI

blah, blah, blah

bar = foo(a,b);

blah, blah, blah

blah, blah, blah

bar = foo(a,b);

blah, blah, blah

int foo(int x, int y ) { if (x>100)

return(y-2); else if (x>10)

return(y-x); else

return(x+y);}

int foo(int x, int y ) { if (x>100)

return(y-2); else if (x>10)

return(y-x); else

return(x+y);}

ClientClient

ServerServer

protocol

Remote Procedure Call (RPC)

RPCRPC


Java RMI

Why RPC/RMI

Advanced form of communication Sockets and MPI: data transfer RPC/RMI: control transfer

Transparency in function calls No distinguish between local and remote calls (in theoretical) Also applied to IPC on the same machine

Ease of use Compiled-time argument type checking Automatic stub generation

Calling a function/method at a remote server:

IPC : Inter-Process Communication


Java RMI

Middleware Layers

Applications

Middlewarelayers Request reply

protocoleXternal Data Representation(XDR)

Operating System

RPC, RMI, and events

分層負責 , 分工合作


Java RMI

RPC – Remote Procedure CallThere are a number of popular RPC specifications.

Sun RPC is widely used.

NFS (Network File System) is RPC based.

RPC clients are processes that call remote procedures.

RPC servers are processes that include procedure(s) that can be called by clients.

Rich set of support tools.The RPC Library is a collection of tools for automating the creation of RPC clients and servers.


Java RMI

Sun RPCRPCGEN command There is a tool for automating the creation of RPC

clients and servers. The program rpcgen does most of the work for you.

This rpcgen is usually knows as RPC compiler. The input to rpcgen is a protocol definition in the form

of a list of remote procedures and parameter types.


Java RMI

RPCGEN

Input File

rpcgen

Client Stubs XDR filters header file Server skeleton

C Source CodeC Source Code

ProtocolProtocolDescriptionDescription

foo_clnt.c foo_svc.c

foo.xx

% rpcgen –C foo.xx

foo_xdr.c foo.h


Java RMI

RPC Programming

RPC Library XDR routines RPC run time library

call rpc service

register with portmapper

dispatch incoming request to correct procedure

Program Generatorrpcgen


Java RMI

RPC Run-time Library

High- and Low-level functions that can be used by clients and servers.

High-level functions provide simple access to RPC services. For client: int callrpc( . . . ) For server: int registerrpc( . . . ) svc_run() is a dispatcher on server

A dispatcher waits for incoming connections and invokes the appropriate function to handle each incoming request.


Java RMI

Procedure Arguments

To reduce the complexity of the interface specification, Sun RPC includes support for a single argument to a remote procedure.*Typically the single argument is a structure that contains a number of values.

* Newer versions can handle multiple args.


Java RMI

Procedure Identification

Each procedure is identified by: Hostname (IP Address) Program Identifier (32 bit integer) Procedure Identifier (32 bit integer)

Program Version identifierfor testing and migration.


Java RMI

Program Identifiers

Each remote program has a unique ID.

Sun divided up the IDs:

0x00000000 - 0x1fffffff

0x20000000 - 0x3fffffff

0x40000000 - 0x5fffffff

0x60000000 - 0xffffffff

SunSun

SysAdmin SysAdmin

TransientTransient

ReservedReserved


Java RMI

Procedure Identifiers &Program Version Numbers

Procedure Identifiers usually start at 1 and are numbered sequentially

Version Numbers typically start at 1 and are numbered sequentially.


Java RMI

Iterative ServerSun RPC specifies that at most one remote procedure within a program can be invoked at any given time.

If a 2nd procedure is called, the call blocks until the 1st procedure has completed.

Having an iterative server is useful for applications that may share data among procedures.

Example: database - to avoid insert/delete/modify collisions.

We can provide concurrency when necessary...


Java RMI

RPC example (1/7)This program shows you how to use a server program, a client program and an interface definition file to let the client program call the functions in the server program and get the results.Files: ① test_proc.c --- the server file ② test_client.c --- the client file ③ test.xx --- the Interface Definition file of RPC Files generated by rpcgen: rpcgen –C test.xx

test_clnt.c test_svc.c test.h


Java RMI

RPC example (2/7)File test_proc.c (1/1) for server side

#include "test.h"int *addd_1_svc(int *argp, struct svc_req *rqstp){ static int result; result = *argp + 1; return (&result);}int *decc_1_svc(int *argp, struct svc_req *rqstp){ static int result; result = *argp - 1; return (&result);}


Java RMI

RPC example (3/7)File test_client.c (1/3) for client side

#include "test.h" /* test_client.c , page1 */void test_prog_1(char *host){ CLIENT *clnt; int *result_1; int addd_1_arg; int *result_2; int decc_1_arg; #ifndef DEBUG clnt = clnt_create(host, TEST_PROG, TEST_VERS, "netpath"); if (clnt == (CLIENT *) NULL) /* NULL is 0 */ { clnt_pcreateerror(host); exit(1); } /* to be continued */


Java RMI


#endif /* DEBUG */ /* test_client.c , page2 */ scanf ("%d",&addd_1_arg); scanf ("%d",&decc_1_arg); result_1 = addd_1(&addd_1_arg, clnt); if (result_1 == (int *) NULL) { clnt_perror(clnt, "call failed"); } result_2 = decc_1(&decc_1_arg, clnt); if (result_2 == (int *) NULL) { clnt_perror(clnt, "call failed"); } printf ("addd_1_result = %d\n",*result_1); printf ("decc_1_result = %d\n",*result_2); #ifndef DEBUG clnt_destroy(clnt); #endif/* DEBUG */} /* test_prog_1 *//* to be continued */


Java RMI


/* test_client.c , page3 */main(int argc, char *argv[]){ char *host; if (argc < 2) /* no host name given */ { printf("usage: %s server_host\n", argv[0]); exit(1); } host = argv[1]; test_prog_1(host);}


Java RMI

RPC example (6/7)File : test.xx

program TEST_PROG{ version TEST_VERS { int ADDD(int)=1; int DECC(int)=2; }=1;}=0x31234567;

rpcgen –C test.xx


Java RMI

RPC example (7/7)Use rpcgen , C compiler, and Linking/loader By rpcgen test.xx , you can get test_clnt.c, test_svc.c and test.h. Compile/link on the client

gcc -o test test_client.c test_clnt.c -lnsl

Compile/link/run on the server (ccsun2.csie.nctu.edu.tw)

gcc -o test_svc test_svc.c test_proc.c -lrpcsvc -lnsl

./test_svc&

Run clien program on the client

./test ccsun2.csie.nctu.edu.tw

Demo on Sun machines


Java RMI

rpcgen –C test.xx


Java RMI

Test RPC -- Server Side


Java RMI

Test RPC -- Client Side

把第一個數加 1,

把第二個數減一

輸入兩列 : 57 89


Java RMI

Another example of rpcgen file

struct readargs {FileIdentifier f;FilePointer position;Length length;

};

program FILEREADWRITE { version VERSION {

void WRITE(writeargs)=1;Data READ(readargs)=2;2

}=2;} = 9999;

const MAX = 1000;typedef int FileIdentifier;typedef int FilePointer;typedef int Length;struct Data {

int length;char buffer[MAX];

};struct writeargs {

FileIdentifier f;FilePointer position;Data data;

};


Java RMI

High-Level Library Limitation

The High-Level RPC library calls support UDP only (no TCP).

You must use lower-level RPC library functions if you want to use TCP.

The High-Level library calls do not support any kind of authentication.


Java RMI

Low-level RPC Library

Full control over all IPC options TCP & UDP Timeout values Asynchronous procedure calls

Multi-tasking Servers

Broadcasting

IPC : Inter-Process Communication


Java RMI

The General RMI Architecture

The server must first bind its name to the registry

The client lookup the server name in the registry to establish remote references.

The Stub serializing the parameters to skeleton, the skeleton ( 框架 ) invoking the remote method and serializing the result back to the client stub ( 存根 ).

RMI Server

skeleton

stub

RMI Client

Registry

bind

lookupreturn call

Local Machine

Remote Machine


Java RMI

The Stub ( 存根 ) and Skeleton (框架 )

A client invokes a remote method, the call is first forwarded to stub.The stub is responsible for sending the remote call over to the server-side skeleton

The stub opening a socket to the remote server, marshaling the object parameters and forwarding the data stream to the skeleton.A skeleton contains a method that receives the remote calls, unmarshals the parameters, and invokes the actual remote object implementation.Java RMI is NOT an all-purpose ORB architecture like CORBA

Stu

b

RMI Client RMI Server

skeleton

return

call


Java RMI

Stub

Stub ( 存根 ; 客戶端代理 ) Client side Acts as an implementation of a remote interface Communicates with the real object over the network The stub class is generated from corresponding remote

class by the RMI compiler rmic

Note: As of the J2SE 5.0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5.0 VMs.


Java RMI

skeleton

Skeleton ( 框架 ; 服務端代理 ) Server side Carries on a conversation with the stub; Reads the parameters for the method call from the link Call the real remote service Writes the return value from the service back to the stub

Note: Before J2SE 5.0 (i.e., JDK 1.4 and older version,

rmic is required to generate the skeleton ???_Skel.classAnd ???_Stub.class for client (Where ??? Is your server Class name)


Java RMI

JVM Asociated

to ActivationGroup

RMI (in Java)

Client Code

network

NamingService

Server Object

ActivationDaemonClient

Stub

ServerSkeleton

Implement “Factories” using declarative descriptions of activatable objects

One JVM per ActivationGroup. Automatically launched by Activation daemon and contains (potentially) many small scale, semi-independent servers which can share resources (like connection pools) and which live under the same security restrictions

“Flat” directory structure which attempts to provide some notion of location transparency-- client code uses a single name to find a server


Java RMI

Java Interfaces

Similar to ClassNo implementation! All methods are abstract (virtual function for C++ ).Everything is public.No constructoran Interface is an API that can be implemented by a Class.

In Java a class can only extend a single superclass (single inheritence). But a Java class can implement any number of interfaces.


Java RMI

Serializable interface

In Java a class can only extend a single superclass (single inheritence).

A class can implement any number of interfaces. end result is very similar to multiple inheritence.

A class is Serializable if it implements the interface Serializable. A Serializable class is one whose instances can be marshaled (turned into a linear sequence of bits). Serializable objects can be transmitted from one computer to another, as well as be stored into a file.


Java RMI

Java RMI classesJava.rmi.Remote Interface supporting remote objects

java.rmi.server.UnicastRemoteObject Continuously running server

java.rmi.activation.Activatable Server started by rmid daemon

java.rmi.Naming Lookup: Returns stub given a name

Java.rmi.registry.Registry , LocateRegistryjava.rmi.RMISecurityManager Validates rights to access downloaded object


Java RMI

RMI Adds a few layers to TCP/IP

Server App.

Skeleton

Remote Reference

Transport

Client App.

Stubs

Remote Reference

Transport


Java RMI

Remote reference layer

Defines and supports the invocation semantics of the RMI connection

Provides a RemoteRef object that represents the link to the remote service implementation object

The stub objects use the invoke( ) method in RemoteRef to forward the method call


Java RMI

Transport layer

Provides basic connectivity makes the connection between JVMs

Based on TCP/IP connections between machines in a network

The network works are done by the client stub and the server Skelton.


Java RMI

Finding Remote Objects

It would be awkward if we needed to include a hostname, port and protocol with every remote method invocation.

RMI provides a Naming Service through the RMI Registry that simplifies how programs specify the location of remote objects. This naming service is a JDK utility called rmiregistry that runs at a well known address (by default).


Java RMI

Find Servers using Naming Service

Simple interface to registry

Implemented via 5 static methods on an object:

public static String[] list(String name) public static Remote lookup(String name) public static void bind(String name, Remote obj) public static void rebind(String name, Remote obj) public static void unbind(String name)


Java RMI

java.rmi.Naming


Java RMI

java.rmi.registry.LocateRegistry


Java RMIjava.rmi.registry.Registry


Java RMI

Steps for Developing an RMI System

1. Define the remote interface extends java.rmi.Remote that declares the methods that will be available remotely.

2. Develop the remote server class by implementing the remote interface. The server program must create a remote object and register it with the naming service.

3. Develop the client program.4. Compile the Java source files.5. Use rmic to Generate the client stubs and server skeletons.6. Start the RMI registry.7. Start the remote server objects.8. Run the client


Java RMI

RMI Deployment

RMI Deployment( 佈署 ): Where does the server program finds it’s classes? Where does the client program find it’s classes? How are classes loaded from client to server and vice-versa?

Remember that Object Serialization does not send the classes, only the data

Deployment on client two ways to get the class files to the client

Copy class files for all stub classes to the client manually

Client dynamically download stub class from Web server


Java RMI

Dynamic Loading on Client (1/2)

In principle, modifying your RMI application to allow dynamic loading of stub classes is now straightforward: Install the stub classes in a Web Server document directory. Set the java.rmi.server.codebase property for the server application, to

reference that Web Server directory. (see below) Create a security policy file on the client. Set the java.security.policy property for the client application. Set a security manager in the client.

This also works for any classes (not just stubs) whose serialized form may be communicated via remote method calls. You just need to reinterpret “server” and “client” application according to

the direction the serialized object moves—as “source” and “destination” application.

javaw –Djava.rmi.server.codebase=http://www.mit.edu/ggyy/ HelloServer


Java RMI

Dynamic Loading on Client (2/2) Usual CLASSPATH variable “local codebase”

Set this while running both the server and the client but not rmiregistry RMI client needs stubs from server

Stubs downloaded from the server to the client using the java.rmi.server.codebase property

RMI server may need classes from the clientClasses downloaded from the client to the server using the java.rmi.server.codebase property setup by the client

RMI registry needs to find stub classesIf it finds them from CLASSPATH it will not convey the “true” code base associated with the stub class even if the server sets it.

Searches “local” code base initially, then searches the “java.rmi.server.codebase”


Java RMI

Setting the Security Manager

In an RMI application, if no security manager is set, stubs and classes can only be loaded from the local CLASSPATH.To enable dynamic loading, issue the command: System.setSecurityManager(new RMISecurityManager()) ;

at the start of the program.You should do this in any application that may have to download code—in the simple examples considered so far this means RMI clients that need to download stubs.This isn’t the end of the story. You also have to define a new property: the java.security.policy property. In simple cases this java.security.policy property is needed for

clients, whereas java.rmi.server.codebase is needed for servers.


Java RMI

Defining a Security Policy

The simplest security policy you can define is a plain text file with contents: grant { permission java.security.AllPermission "", "" ; } ;

This policy allows downloaded code to do essentially anything the current user has privileges to do: Read, write and delete arbitrary files; open, read and write to arbitrary

Internet sockets; execute arbitrary UNIX/Windows commands on the local machine, etc.

It is a dangerous policy if there is any chance you may download code from untrustworthy sources (e.g. the Web).

For now you can use this policy, but please avoid dynamically loading code you cannot trust!


Java RMI

The java.security.policy Property

If the text file containing our security policy is called (for example) policy.all, the original HelloClient example might now be run as follows:

java –Djava.security.policy=policy.all HelloClient

Alternatively this property can be set inside the program using System.setProperty().


Java RMI

RMI scenario (1/2)Downloading Stubs


Java RMI

RMI scenario (2/2)

Downloading Classes


Java RMI

Creating Remote object

1. Define an interface which extends Remote interface2. Create the server program which implements that interface3. Server class should extend UnicastRemoteObject or you

can use use UnicastRemoteObject.exportObject(svrObj, 0);4. Compile the Java program5. Create the Stub for client using rmic command or other tools



Java RMI

Create the Stub

A. In JBuilder use “JNI/RMI” tab in class properties to generate it automatically

B. By hand: use rmic tool:

rmic ComputeEngine



Java RMI

Server Details – extending Remote

Create an interface the extends the java.rmi.Remote interface. This new interface includes all the public methods that

will be available as remote methods.

import java.rmi.*;

public interface MyRemote extends Remote { public int foo(int x) throws RemoteException;

public String blah(int y) throws RemoteException;

. . .

}


Java RMI

How the interface will be used

Class for your Remote Object

Your Interface UnicastRemoteObject

Remote Interface Class RemoteServer

extends

implementsextends

extendsprovides methods needed by


Java RMI

Server Details – Implementation Class

Create a class that implements the interface. The class should also extend UnicastRemoteObject; or you

can create the server object svrObj and then use the static function UnicastRemoteObject.exportObject(svrObj, 0);

This class needs a constructor that throws RemoteException !

This class is now used by rmic to create the stub and skeleton code.



Java RMI

Generating stubs and skeleton

Compile the remote interface and implementation:

> javac MyRemote.java MyRemoteImpl.java

Use rmic to generate MyRemoteImpl_stub.class, MyRemoteImpl_skel.class

> rmic MyRemoteImpl



Java RMI

Server Detail – main( )

The server main( ) needs to: create a remote object. register the object with the Naming service.

public static void main(String args[]) {

try {

MyRemoteImpl r = new MyRemoteImpl();

javaNaming.bind(“joe”,r);

} catch (RemoteException e) {

. . .


Java RMI

Client DetailsThe client needs to ask the Naming service for a reference to a remote object. The client needs to know the hostname or IP address

of the machine running the server. The client needs to know the name of the remote

object.

The Naming service uses URLs to identify remote objects.

rmi://hostname/objectname


Java RMI

Using The Naming service

Naming.lookup() method takes a string parameter that holds a URL indicating the remote object to lookup.

rmi://hostname/objectname

Naming.lookup( ) returns an Object!

Naming.lookup( ) can throw RemoteException MalformedURLException


Java RMI


Java RMI


Java RMI


Java RMI


Java RMI


Java RMI

RMI registry (1/2)

A naming service Maps names to remote objects Provides clients with a mechanism to find remote services

running on RMI serversEssential operations: bind/rebind, unbind, lookup Bind adds a service entry to the registry Unbind removes a service entry from the registry Lookup allows clients to find the service’s address using

service nameNames in the registry use unique names Recommend the name of the remote class that implements

the remote interface


Java RMI

RMI registry (2/2)

To send a message to a remote “server object,” The “client object” has to find the object

Do this by looking it up in a registry The client object then has to marshal the parameters (prepare them for

transmission)Java requires Serializable parametersThe server object has to unmarshal its parameters, do its computation, and marshal its response

The client object has to unmarshal the responseFor accessing a remote registry, use the following URL form rmi://host:port/serviceName host is the machine on which the registry is running The registry is listening on the port (default 1099)


Java RMI


Java RMI


Java RMI


Java RMI

Start the Java RMI registryBy default, the registry runs on TCP port 1099. To start a registry on a different port, specify the port number from the command line. For example, to start the registry on port 2001 on a Windows platform:

start rmiregistry 2001 If the registry will be running on a port other than 1099, you'll need to specify the port number in the calls to LocateRegistry.getRegistry in the Server and Client classes. For example, if the registry is running on port 2001 in this example, the call to getRegistry in the server would be: Registry registry =

LocateRegistry.getRegistry(2001);


Java RMI


Java RMI

Stateful/Stateless Servers

Stateful servers: Servers keep track of client information. RPC/RMI reply depends on that client information. Pros: Simplify client design Cons: A server crash loses client information. A client crash leaves old

client information at server. At-most-once invocation semantics (Java RMI takes this design.)

Stateless servers: Clients must maintain Inter-call information. RPC/RMI reply is always the same. At-least-once invocation semantics (Some RPC implementations take

this design.)


Java RMI

Other Technologies CORBA XML based

SOAP / Web Service J2EE/EJB MicroSoft’s COM, DCOM MicroSoft’s .NET

Has Common Language RuntimeTight Integration of Web Services and XMLMultiple language integration

However only one platform Windows


Java RMI

Reference RMI docs

java.sun.com/products/jdk/rmi/ Java Tutorial on RMI:

http://java.sun.com/j2se/1.5.0/docs/guide/rmi

JavaIDLjava.sun.com/docs/books/tutorial/idl

java.sun.com/products/jdk/idl/

www.omg.org/news/begin.htm

Jini -- http://www.jini.org/www.artima.com/jini/resources


Java RMI

Programming Paradigms

Imperative Programming (FORTRAN, C, Pascal, …) The most common programming paradigm

Functional Programming (LISP, …)

Logic Programming (Prolog)

(Declarative programming language; 宣告式語言 )

Object-Oriented Programming

(Smalltalk, C++, Java, …)

Simply using C++/Java constructs does not automatically lead to well-organized Object-Oriented Programs.


Java RMI

Why OO Programming?Better concepts and tools to model and represent the real world as closely as possible (including concurrency, e.g., in Windows GUI)=> model of reality=> behavior modelingBetter reusability & extensibility (inheritance)=> reduce the time/cost of development

Enhanced maintainability & improved reliability – “Encapsulation” and “Information Hiding” Object only accessible through the external interface Internal implementation details are not visible outside Localized changes to implementation of classes Completeness: all required operations are defined Independent testing and maintenance

Help writing good program more easily


Java RMI

From function to Distributed computingFunction, Subroutine, ProcedureDLL (share Library)RPC, RMICORBA (Common Object Request Broker Architecture)XML, SOAP, Web serviceODBC, JDBCJava EE (J2EE), EJBDCOM, .NET (dot NET), C# ( 請寫出 C# 要如何唸 ?)parallel computingpervasive computing(普及計算 )、 ubiquitous computingGrid computing(網格運算 )Cloud computing(雲端運算 )

JINI: Jini Is Not Initials GNU: GNU Is Not Unix


Java RMI

RMI example from Sun Java(1/4)C:\jtest\RMI>java lineno < Hello.java 1 //Hello.java 2 //package example.hello; 3 import java.rmi.Remote; 4 import java.rmi.RemoteException; 5 public interface Hello extends Remote { 6 String sayHello() throws RemoteException; 7 }// interface HelloC:\jtest\RMI>java lineno < Server.java 1 //Server.java 2 //package example.hello; 3 import java.rmi.registry.Registry; 4 import java.rmi.registry.LocateRegistry; 5 import java.rmi.RemoteException; 6 import java.rmi.server.UnicastRemoteObject; 7 public class Server implements Hello { 8 public Server( ) {} 9 public String sayHello() { 10 return "Hello, world!"; 11 }


Java RMI

RMI example from Sun Java(2/4)

12 public static void main(String args[]) { 13 try { 14 Server obj = new Server(); 15 Hello stub = (Hello)

UnicastRemoteObject.exportObject(obj, 0); 16 17 // Bind the remote object's stub in the registry 18 Registry registry = LocateRegistry.getRegistry(); 19 registry.bind("Hello", stub); 20 21 System.err.println("Server ready"); 22 } catch (Exception e) { 23 System.err.println("Server exception: " +

e.toString()); 24 e.printStackTrace(); 25 } 26 } // main( 27 }//class Server


Java RMI

RMI example from Sun Java(3/4)C:\jtest\RMI>java lineno < Client.java 1 //Client.java 2 //package example.hello; 3 import java.rmi.registry.LocateRegistry; 4 import java.rmi.registry.Registry; 5 public class Client { 6 private Client() {} 7 public static void main(String[] args) { 8 String host = (args.length < 1) ? null : args[0]; 9 try { 10 Registry registry = LocateRegistry.getRegistry(host); 11 Hello stub = (Hello) registry.lookup("Hello"); 12 String response = stub.sayHello( ); 13 System.out.println("response: " + response); 14 } catch (Exception e) { 15 System.err.println("Client exception: " + e.toString()); 16 e.printStackTrace(); 17 } 18 }//main( 19 }// class Client


Java RMI

RMI example from Sun Java(4/4)C:\jtest\RMI>javac *java

C:\jtest\RMI>start rmiregistryC:\jtest\RMI>javaw Server

C:\jtest\RMI>java Clientresponse: Hello, world!

C:\jtest\RMI>java Client 192.168.1.2response: Hello, world!

C:\jtest\RMI>java Client 192.168.1.1Client exception: java.rmi.ConnectException: Connection refused to host:

192.168.1.1; nested exception is: java.net.ConnectException: Connection timed out: connect


Java RMI

Hint to deploy RMI

JDK 1.4 and Older version Compile all *.java rmic Server Copy *stub*class to Client side Copy *skel* to Server Server side: start rmiregistry Server side: javae Server Client side: java Client

JDK 1.5 and later version ( rmic is no longer needed ) Compile all *.java Server side: start rmiregistry Server side: javae Server Client side: java Client

Server requires: Hello.java, Server.javaClient requires: Hello.java, Client.java


Java RMI

Web servicesA collection of XML-based technologies developed by the e-business community to address issues of: Service discovery : UDDI + WSDL Interoperable data exchange and/or application invocation :

HTTP + XML + SOAP (Simple Object Access Protocol) Service compositions (workflow, business processes)

The programming effort and maintainability is roughly the same both for Web Services and CORBAMajor developers include: Apache, IBM, HP, SUN & Microsoft (.NET)

http://www.webservices.org/


Java RMI

W3C (working group) Web service definition

"A Web service is a software application identified by a URI, whose interfaces and bindings are capable of being defined, described and discovered as XML artefacts. A Web service supports direct interactions with other software agents using XML based messages exchanged via internet-based protocols."

http://www.w3c.org/TR/2002/WD-wsa-reqs-20020819


Java RMI

Web Services Protocol Stack


Java RMI

SOAPSimple Object Access Protocol http://www.w3c.org/TR/SOAP/

A lightweight protocol for exchange of information in a decentralised, distributed environmentTwo different styles to use: to encapsulate RPC calls using the extensibility and

flexibility of XML …or to deliver a whole document without any method

calls encapsulated


Java RMI

WSDL

Web Services Definition Language http://www.w3.org/TR/wsdl/

An XML-based language for describing Web Services what the service does (description) how to use it (method signatures) where to find the service

WSDL does not depend on the underlying protocol


Java RMI

UDDI (and alternatives)

Universal Description, Discovery and Integration http://www.uddi.org

UDDI creates a platform-independent, open framework & registry for: Describing services Discovering businesses Integrating business services

The UDDI may be less used than predicted, especially on the Internet levelBioMoby - an alternative for Life Sciences domain?


Java RMI

Sending requests,

getting results

Sending requests,

getting results

Waiting for requests

(known location,known port)



Data as name/value pairs

Traditional CGI-based approach

cgi-bin scripts: Data transmitted as name-value pairs (HTML forms) Transport over (state-less) HTTP protocol no standards for keeping user sessions (state-fullness) server side: a script is called


Java RMI

Sending requests,

getting results

Sending requests,

getting results





Data in binary format

CORBA-based approach

CORBA: (Common Object-Request-Broker Architecture) Data transmitted as objects (at least it looks like that) Transport (usually) over well standardised IIOP protocol user sessions (state-fullness) very inter-operable server side: an RPC call is made


Java RMI

Sending requests,

getting results

Sending requests,

getting results





Data in XML format

SOAP-based communication(Web Service)

SOAP: (Simple Object Access Protocol) Data in a well-defined XML format Transport over various protocols

HTTP, SMTP are the most used, perhaps because they are firewall-friendly

server side: either an RPC call or a message delivered


Java RMI

RPC / RMI

謝謝捧場http://www.csie.nctu.edu.tw/~tsaiwn/java/

蔡文能

Documents

Programming in Java