Chapter 11 Socket Programming in Java · 2017-01-18 · Chapter 11: Objective We show how entities such as IP addresses, ports, and socket addresses are represented by corresponding

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.11.1 .

Chapter 11

Socket

Programming

in Java

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.11.2

Chapter 11: Outline

11.1 INTRODUCTION

11.2 PROGRAMMING WITH UDP

11.3 PROGRAMMING WITH TCP


Chapter 11: Objective

We show how entities such as IP addresses, ports, and socket

addresses are represented by corresponding classes in Java.

We introduce classes in Java that are used in UDP

programming. We then show how we can write simple client-

server programs using the iterative approach. Next, we show

how we can change the server program using the concurrent

approach.

We introduce classes in Java that are used in TCP programming.

We then show how we can write simple client-server programs

using the iterative approach. Finally, we show how we can

change the server program using the concurrent approach.


11-1 INTRODUCTION

In this section we discuss how general

ideas in C network programming, which

we discussed in Chapter 2, can be used

in Java network programming.


11.1.1 Addresses and Ports

Network programming in any language definitely

needs to deal with IP addresses and port numbers.

We briefly introduce how addresses and ports are

represented in Java. We recommend that the reader

compare the representations of these two entities in

C and Java.

IP Addresses

Port Numbers

InetSocketAddress


Table 11.1: Summary of InetAddress class


In this example, we show how we use the second and the

third static methods to get the InetAddress of a site and the

local host (Table 11.2). In line 7, we use the second static

method to get the IP address of the site “forouzan.biz”. In

line 9, we pass an IP address, as a string, to the getByName

method to change it to an InetAddress object. Lines 11 to 13

print the above addresses as stored in the InetAddress

objects. We can use the getHostAddress method to extract

the address part of an InetAddress object as a string in line

15. In line 16, we use the getHostName method to find the

name of a host given the address (using the DNS again).

Example 11.1


Table 11.2: Example 11.1


Table 11.2: Example 11.1 (continued)


In this example, we show how we use the second and the

third static methods to get the InetAddress of a site and the

local host (Table 11.2).

Example 11.2




Table 11.4: Summary of InetSocketAddress class


The program in Table 11.5 shows how we can create a

socket address. Note that the port number is separated by a

colon from the InetAddress in this presentation.

Example 11.3




11.1.2 Client-Server Paradigm

A server in a client-server paradigm can be designed

either as an iterative server or a concurrent server.

An iterative server handles the clients one by one. A

concurrent server can simultaneously serve as many

clients as the computer resources permit.

Client and Server Programs

Socket Interface in Java


11-2 PROGRAMMING WITH UDP

To be consistent with the socket

programming section of Chapter 2, we first

discuss network programming using the

service of UDP, a connectionless service.

We talk about the iterative approach first

and concurrent approach next.


11.2.1 Iterative Approach

UDP provides a connectionless service and

communication is done using chunks of data

called user datagrams. In the iterative

approach, the server serves one datagram at a

time. The rest of the arrived datagrams need to

wait, no matter whether they are coming from

the same client or other clients.


11.2.1 (continued)

Sockets Used for UDP

Classes

DatagramSocket Class

DatagramPacket Class

UDP Client Design

Client Program

The main Method

The Methods in UDPClient Class


11.2.1 (continued)

UDP Server

The main Method

The Methods in UDPServer Class

Server Program


Figure 11.1: Sockets for UDP communication

1 Request

2Response

4Response

3 Request


Table 11.6: Some methods in DatagramSocket class


Table 11.7: Some methods in DatagramPacket class


Figure 11.2: Design of the UDP Client


Table 11.8: A simple UDP client program


Table 11.8: A simple UDP client program (continued)






Figure 11.3: Design of the UDP Server


Table 11.9: A simple UDP server program


Table 11.9: A simple UDP server program (continued)






The simplest example is to simulate the standard echo

client/server. A short message is sent by the client. The

message is exactly echoed back. Although the standard uses

the well-known port 7, to simulate it, we use the port

number 52007 for the server.

Example 11.4


Example 11.4 (Continued)


In this example, we change our server to a simple date/time

server. It returns the local date and time at the location

where the server is running.

Example 11.5


Example 11.5 (continued)


In this example, we need to use our simple client-server

program to measure the time (in milliseconds) that it takes

to send a message from the client to the server.

Example 11.6


Example 11.6 (continued)


11.2.2 Concurrent Approach

The iterative approach to the UDP server

program is good enough for most applications

because, after processing and sending one

datagram, the server is ready to serve other

clients. However, if the processing of a

datagram takes a long time, a client may

monopolize the server. The concurrent server

programs were designed to solve this problem

using threads.

Server Program


Table 11.10: A concurrent UDP server program


Table 11.10: A concurrent UDP server program (continued)






We repeat Example 11.5 using the concurrent approach. We

need several computers to simultaneously send the request

and get the response.

Example 11.7


We repeat Example 11.6 using the concurrent approach. We

need several computers to simultaneously send the request

and get the response.

Example 11.8


11-3 PROGRAMMING WITH TCP

We are now ready to discuss network

programming using the service of TCP, a

connection-oriented service. We first

discuss how to write a client and a server

program using the iterative approach. We

then show how we can change the server

program to make it concurrent.


11.3.1 Iterative Approach

Although the iterative approach to TCP

programming is rare, it is the foundation of the

concurrent approach. In this approach, a server

handles clients one by one. When the server starts

serving a client, the other clients need to wait.


11.3.1 (continued)

Two Types of Sockets

Classes

ServerSocket Class

Socket Class

TCP Client Design

TCP Client Program

The main Method

The Methods in TCPClient Class


Figure 11.4: ServerSocket and Socket objects in TCP communication

Connection establishment1

Connection establishment4

Create

2Data transfer and termination

3

Data transfer and termination

6

Create

5


Table 11.11: Summary of ServerSocket class


Table 11.12: Summary of Socket class


Figure 11.5: Design of the TCP Client


Table 11.13: A simple TCP client program


Table 11.13: A simple TCP client program (continued)






Figure 11.6: Design of the TCP Server for each client connection


Table 11.14: A simple TCP server program


Table 11.14: A simple TCP server program (continued)






11.3.2 Concurrent Approach

The iterative approach to the TCP server program

can allow a client to monopolize a server and does

not allow the server to pay attention to the

demands of other clients. The concurrent server

programs were designed to solve this problem. In

Java, this task is done using multiple threads.

Server Program


Table 11.15: A concurrent TCP server program


Table 11.15: A concurrent TCP server program (continued)






Chapter 11: Summary

Network programming definitely needs to deal with IP addresses

and port numbers. In Java, an IP address is an instance of the

InetAddress class. A port number is represented as an integer. In

Java, a socket address, a combination of an IP address and a

port number, is represented by the SocketAddress class.

In the client-server paradigm, communication occurs between

two application programs, a client and a server. A client is a

finite program that requests service from a server. A server in a

client-server paradigm can be designed either as an iterative

server or as a concurrent server. An iterative server handles the

clients one by one. A concurrent server can simultaneously serve

as many clients as the computer resources permit.


Chapter 11: Summary (continued)

Although there are a few ways to write a client or server

application program, we discussed only the socket interface

approach. The whole idea is to create a new abstract layer, the

socket interface layer, between the operating system and the

application layer.

Java implementation of application programming with UDP

uses two classes: DatagramSocket and DatagramPacket. The

first is to create a socket object; the second is to create the

datagrams exchanged. Java implementation of application

programming with TCP uses two classes: ServerSocket and

Socket. The first is used only during the connection

establishment; the second is used for the rest of the

communication.

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Chapter 11 Socket Programming in Java · 2017-01-18 · Chapter 11: Objective We show how entities such as IP addresses, ports, and socket addresses are represented by corresponding