java programming: advanced topics 1 networking programming chapter 11

Java Programming: Advanced Topics

1

Networking Programming

Chapter 11


2

Objectives

• Perform network I/O using the core classes in the package java.net

• Write programs that establish connections to URLs and perform stream I/O between URLs

• Read and write data to local and remote sites using TCP/IP sockets and datagram sockets


3

Objectives (Cont.)

• Use Remote Method Invocation (RMI) to develop classes of objects that are accessible from a server

• Learn the steps involved in compiling and deploying an application that uses RMI


4

Objectives (Cont.)

• Be introduced to the Java Naming and Directory Interface (JNDI)

• Discover the relationship between CORBA, RMI-IIOP, and the Java Interface Definition Language (IDL)


5

Introduction

• The Java platform includes a package java.net to perform input and output (I/O) operations over the network

• Core classes of the java.net package support URLs, TCP/IP sockets, or datagram sockets


6

Working with URLs

• URLs begin with a protocol specification followed by a colon and two forward slashes (://) and the host name, along with optional file and port information

• To exchange information with a URL, you must create a URLConnection by calling the method openConnection for a URL


7

The Use of the URL and URLConnection Objects


8

The Use of the URL and URLConnection Objects (Cont.)


9

Working with URLs (Cont.)

• Uniform Resource Identifier (URI) technology has become commonly used in technical specifications in place of the term URL

• The class java.net.URI contains a method, toURL, which can be used to construct a URL object from a URI object


10

Working with Sockets

• Socket: an abstraction of the end points of connections between processes or applications

• The Java platform supports two types of sockets:– TCP/IP– datagram


11

TCP/IP Sockets

• A TCP/IP socket is connection-oriented• Create a Socket object, ask the socket for its

input stream and output stream• To perform stream I/O to and from a TCP/IP

socket, use the methods Socket.getInputStream and Socket.getOutputStream

• Use the ServerSocket class to create the server side of a TCP/IP socket


12

Datagram Sockets

• Datagram sockets send packets that contains information that identifies the network destination in addition to the content of your message

• The class DatagramPacket represents these packets

• The User Datagram Protocol (UDP) used by these sockets makes no attempt to recover from lost or damaged packets


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An Example Datagram Socket Server Program


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An Example Datagram Socket Server Program (Cont.)


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An Example Datagram Socket Server Program (Cont.)


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An Example Datagram Socket Client Program


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An Example Datagram Socket Client Program (Cont.)


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Remote Method Invocation• Remote Invocation Method (RMI) is a

technology that allows programmers to call directly the methods of Java objects that reside on other systems

• Client programs use Object Request Brokers (ORBs) to obtain references to these remote objects

• Marshaling: the technique used to forward the parameters to the remote object


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Remote Method Invocation• Stub classes act as local surrogates for remote

objects to provide access to the remote objects• Skeleton classes marshal and unmarshal

parameters and return values between the stub and the remote object

• On the remote system, a skeleton object receives this byte stream and uses a technique called unmarshaling to deserialize the contents of the parameter list


20

Flow of a Remote Method Call


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Developing a Remote Class of Objects

• The Remote interface is a marker interface• To make an interface available remotely via

RMI, it should extend the java.rmi.Remote• All methods in the interface must indicate that

they might throw a java.rmi.RemoteException


22

Remote Interface


23

Developing an RMI Server Class


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Developing an RMI Server Class (Cont.)


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Developing an RMI Client Class


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Developing an RMI Client Class (Cont.)


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Running the Server and Client Programs

• Compile server and client files using the javac compiler

• Create the stub and skeleton classes by using the rmic command

• Start the RMI registry program by typing:rmiregistry

• Start the server program and supply the codebase for the stub and skeleton files

• Start the client program


28

JNDI

• Sun developed the Java Naming and Directory Interface (JNDI)

• JNDI is not itself a naming or directory service, but is a unified interface to multiple naming and directory services that already exist for enterprise development


29

JNDI Packages


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JNDI Packages (Cont.)


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Corba, RMI-IIOP, and IDL• Common Object Request Broker Architecture

(CORBA) is a generic architecture for defining and using remote objects

• A consortium of companies, known as the Object Management Group (OMG), developed the CORBA standard

• CORBA ORBs use Internet Inter-ORB Protocol (IIOP)


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Corba, RMI-IIOP, and IDL (Cont.)

• The interfaces of CORBA objects are defined using a language called Interface Definition Language (IDL)

• Java platform SDK provides a tool called idlj that generates the Java bindings for the specified IDL file


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Summary

• The java.net package supports network programming

• The core classes of the java.net package support URLs, TCP/IP sockets, or datagram sockets

• To exchange information with a URL, you must create a URLConnection object

• TCP/IP sockets are connection-oriented, and datagram sockets use packets


34

Summary (Cont.)

• Remote Invocation Method (RMI) is a technology that allows programmers to call directly the methods of Java objects that reside on other systems

• The Java Naming and Directory Interface (JNDI) is a unified interface to multiple naming and directory services that already exist for enterprise development

• Common Object Request Broker Architecture (CORBA) is a more generic architecture for defining and using remote objects

java programming: advanced topics 1 networking programming chapter 11

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