计算机网络教程自顶而下方法(第十一章)

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.
Table 11.4: Summary of InetSocketAddress class
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Example 11.3
Client and Server Programs
Socket Interface in Java
1Байду номын сангаас.15
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11.4
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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.
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.
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Table 11.3: Example 11.2
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11.16
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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.
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Table 11.2: Example 11.1
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IP Addresses Port Numbers InetSocketAddress
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Table 11.1: Summary of InetAddress class
11.1 INTRODUCTION 11.2 PROGRAMMING WITH UDP 11.3 PROGRAMMING WITH TCP
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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.
Chapter 11 Socket Programming in Java
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Chapter 11: Outline
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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.
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 clientserver 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.
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Example 11.1
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 “”. 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).