谈谈TCP和UDP的一些简单应用

<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> 网络编程中最重要的就是SOCKET，它其实也就是监听端口的原理。和我们用手机发短信的原理应该是大致无二（我是这样理解的），而JAVA最出色的一点也就是“无痛苦连网”。 网络最基本的精神就是让两台机器连接起来，“被呼叫的一方”也就是服务器，而“找人的一方”则叫做客户机，所以说在连接中服务器、客户机也就是一个相对的概念了。而我们对机器的标识主要是通过IP地址和端口来区分的。 “传输控制协议”TCP和“用户数据报协议”是两种不同的协议，JAVA对这两种协议的支持基本是一致的，而它们本身最大的区别也就是发送的可靠性和速率，前者相比后者是可靠协议，后者当然是速度快得多了，下面我们分别用两个SOCKET下演示： eg1: //Clients.java import java.io.*; import java.net.*; public class Clients { public static void main(String[] args) throws Exception { InetAddress addr = InetAddress.getByName(null); Socket socket = new Socket(addr,2000); PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( socket.getOutputStream())),true); byte[] b = new byte[2048]; String msg = new String(b,0,System.in.read(b)); out.println(msg); socket.close(); } } //Servers.java import java.io.*; import java.net.*; public class Servers { public static void main(String[] args) throws Exception { ServerSocket s = new ServerSocket(2000); try{ while(true){ Socket socket = s.accept(); try{ BufferedReader in = new BufferedReader( new InputStreamReader( socket.getInputStream())); StringBuffer sb = new StringBuffer(); int c; while( (c = in.read()) != -1 ){ char ch = (char)c; sb.append(ch); } System.out.println(sb.toString()); }catch(IOException e){ socket.close(); }finally{ socket.close(); } }//while }finally{ s.close(); }//try }//main } 此程式主要用Servers来进行无限监听，而Clients是客户机发送程式，他们的端口全采用2000。 eg2: //UDPsend.java import java.io.*; import java.net.*; /** * This class sends the specified text or file as a datagram to the * specified port of the specified host. **/ public class UDPSend { public static final String usage = "Usage: java UDPSend .../n" " or: java UDPSend -f "; public static void main(String args[]) { try { // Check the number of arguments if (args.length < 3) throw new IllegalArgumentException("Wrong number of args"); // Parse the arguments String host = args[0]; int port = Integer.parseInt(args[1]); // Figure out the message to send. // If the third argument is -f, then send the contents of the file // specified as the fourth argument. Otherwise, concatenate the // third and all remaining arguments and send that. byte[] message; if (args[2].equals("-f")) { File f = new File(args[3]); int len = (int)f.length(); // figure out how big the file is message = new byte[len]; // create a buffer big enough FileInputStream in = new FileInputStream(f); int bytes_read = 0, n; do { // loop until we've read it all n = in.read(message, bytes_read, len-bytes_read); bytes_read = n; } while((bytes_read < len)&& (n != -1)); } else { // Otherwise, just combine all the remaining arguments. String msg = args[2]; for (int i = 3; i < args.length; i ) msg = " " args[i]; message = msg.getBytes(); } // Get the internet address of the specified host InetAddress address = InetAddress.getByName(host); // Initialize a datagram packet with data and address DatagramPacket packet = new DatagramPacket(message, message.length, address, port); // Create a datagram socket, send the packet through it, close it. DatagramSocket dsocket = new DatagramSocket(); dsocket.send(packet); dsocket.close(); } catch (Exception e) { System.err.println(e); System.err.println(usage); } } } //UDPreceive.java import java.io.*; import java.net.*; /** * This program waits to receive datagrams sent the specified port. * When it receives one, it displays the sending host and prints the * contents of the datagram as a string. Then it loops and waits again. **/ public class UDPReceive { public static final String usage = "Usage: java UDPReceive "; public static void main(String args[]) { try { if (args.length != 1) throw new IllegalArgumentException("Wrong number of args"); // Get the port from the command line int port = Integer.parseInt(args[0]); // Create a socket to listen on the port. DatagramSocket dsocket = new DatagramSocket(port); // Create a buffer to read datagrams into. If anyone sends us a // packet containing more than will fit into this buffer, the // excess will simply be discarded! byte[] buffer = new byte[2048]; // Create a packet to receive data into the buffer DatagramPacket packet = new DatagramPacket(buffer, buffer.length); // Now loop forever, waiting to receive packets and printing them. for(;;) { // Wait to receive a datagram dsocket.receive(packet); // Convert the contents to a string, and display them String msg = new String(buffer, 0, packet.getLength()); System.out.println(packet.getAddress().getHostName() ": " msg); // Reset the length of the packet before reusing it. // Prior to Java 1.1, we'd just create a new packet each time. packet.setLength(buffer.length); } } catch (Exception e) { System.err.println(e); System.err.println(usage); } } } 在UDP中主要的类是DatagramSocket()和DatagramPacket()，而在UDPreceive中，被接受的字节是受限制，这些感觉不是太好，既然buf是一个字节数组，我们实在是很奇怪为什么构建器自己不能调查出数组的长度呢？唯一能猜测的原因就是C风格的编程使然，那里的数组不能自己告诉我们它有多大。 而我们实际使用的过程中，当然不仅仅限于这些，其中要考虑有多台客户机来连接服务器，所以要考虑到线程Thread的使用，如果再加上SWING，就可以做一个类似于QQ的SOCKET功能了，这仅仅限于我在学习SOCKET时的一些领悟。供大家参考。 - 主页： http://www.fls-cts.com/kkjvk/