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.javaimport 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.javaimport 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.javaimport 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 argumentsif (args.length < 3)throw new IllegalArgumentException("Wrong number of args");// Parse the argumentsString 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 ismessage = new byte[len]; // create a buffer big enoughFileInputStream in = new FileInputStream(f);int bytes_read = 0, n;do { // loop until we've read it alln = 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 hostInetAddress address = InetAddress.getByName(host);// Initialize a datagram packet with data and addressDatagramPacket 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.javaimport 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 lineint 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 bufferDatagramPacket packet = new DatagramPacket(buffer, buffer.length);// Now loop forever, waiting to receive packets and printing them.for(;;) {// Wait to receive a datagramdsocket.receive(packet);// Convert the contents to a string, and display themString 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/