杂谈socket编程

         最近在写一些与网络编程相关的小工具，不得不再把网络编程的知识再回顾回顾了。一提起网络编程，势必局想到了一位核心人物Socket，是她撑起了网络编程的半边天，使得网络编程得以继续。

         什么是Socket？

        通常也称作"套接字"，应用程序通过Socket向网络发出请求或者应答网络请求。它是在应用层与TCP/IP协议族通信的中间软件抽象层，它是一组接口，用来组织传输的数据。下面就用一张图来说明下“三次握手”：

        

         网络间的通信，是建立在授受双方的，即：服务器与客户端。服务器端时刻处于启动状态，不停地监听着客户端发来的请求信息，并给予应答，当客户端向服务器发来一条数据请求时，服务器接受到了这条请求后，验证成功后，给出回复，建立链接通信，即一次握手。类似数据传输交换、断开链接又是两次握手。下面就以一段代码来做一分析说明吧。（Java版）

服务端：

<span style="font-size:14px;">import java.io.BufferedInputStream;import java.io.BufferedReader;import java.io.File;import java.io.FileFilter;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.PrintWriter;import java.net.ServerSocket;import java.net.Socket;/** * FTP服务器端 * @author xcbeyond * 2014-6-7 22:12:21 */public class FtpServer {public static void main(String[] args) throws Exception{FtpServer server = new FtpServer();server.listen(8800);}        //用来时刻监听来自客户端请求的监听者public void listen(int port) throws Exception{ServerSocket ss = new ServerSocket(port);while(true) {System.out.println("等待客户端连接...");Socket socket = ss.accept();System.out.println("客户连接进来了。");new ClientAgent(socket).start();}}class ClientAgent extends Thread{Socket socket;InputStream in;OutputStream out;public ClientAgent(Socket socket) throws Exception{this.socket = socket;in = socket.getInputStream();out = socket.getOutputStream();}@Overridepublic void run() {BufferedReader in = new BufferedReader(new InputStreamReader(this.in));PrintWriter out = new PrintWriter(this.out,true);//true自动清除缓存   相当于fulsh()try{out.println("text,1");out.println("你好欢迎使用FTP Demo!");while(true) {String cmd = in.readLine();if("?".equals(cmd)) {out.println("text,1");out.println("支持命令：ls,get,?,bye");}else if("ls".equals(cmd)) {listDir(out);}else if(cmd.matches("^get\\s+.+")) {sendFile(cmd,out,this.out);}else{out.println("text,1");out.println("不知可否！");}}}catch(Exception e) {e.printStackTrace();}}private void sendFile(String cmd, PrintWriter out,OutputStream os) throws IOException{String name = cmd.split("\\s+")[1];File file = new File(name);if(!file.exists()){out.println("text,1");out.println("没有找到文件！ "+name);return;}out.println("file,"+file.length()+","+name);InputStream in = new BufferedInputStream(new FileInputStream(file));int b;while((b = in.read())!=-1){os.write(b);}os.flush();in.close();}/** * 列出文件目录 * @param out */private void listDir(PrintWriter out) {File dir = new File(".");File[] files = dir.listFiles(new FileFilter() {public boolean accept(File pathname) {return pathname.isFile();}});out.println("text,"+files.length+1);out.println("在目录："+dir+"中，有文件："+files.length);for (File file : files) {out.println(file.getName());}}}}</span>

客户端：

import java.io.BufferedOutputStream;import java.io.BufferedReader;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.PrintWriter;import java.net.Socket;/** *  * @author xcbeyond * 2014-6-7 23:16:53 */public class FtpClient {Socket socket;OutputStream out;InputStream in;public static void main(String[] args) throws Exception{FtpClient client = new FtpClient();client.open("localhost",8800);}public void open(String host,int port) throws Exception{socket = new Socket(host,port);   //对指定IP，端口的服务程序发出请求，建立通信in = socket.getInputStream();out =socket.getOutputStream();new RequestSender(out).start();new ResponseReceiver(in).start();}class RequestSender extends Thread{OutputStream out;public RequestSender(OutputStream out) {this.out = out;}@Overridepublic void run() {PrintWriter out = new PrintWriter(this.out,true);BufferedReader in = new BufferedReader(new InputStreamReader(System.in));String str;try{while((str = in.readLine())!=null) {out.println(str);}}catch(Exception e){e.printStackTrace();}}}class ResponseReceiver extends Thread {InputStream in;public ResponseReceiver(InputStream in) {this.in = in;}public void run() {BufferedReader in = new BufferedReader(new InputStreamReader(this.in));try{String str;while((str = in.readLine())!=null) {if(str.startsWith("text")) {String num = str.substring(str.indexOf(",")+1);printText(in,Integer.parseInt(num));}else if(str.startsWith("file")){//file,4567，filenamesaveFile(this.in,str);}}}catch(Exception e) {e.printStackTrace();}}/** * 保存文件  * @param in * @param size */private void saveFile(InputStream in, String head) throws IOException{String[] data = head.split(",");int length = Integer.parseInt(data[1]);String name  = data[2];OutputStream out = new BufferedOutputStream(new FileOutputStream("ftp-"+name)); for (int i = 0; i < length; i++) {int b = in.read();out.write(b);}out.close();System.out.println("下载了文件："+name);} /** * 打印出文本内容 * @param in * @param num * @throws Exception */private void printText(BufferedReader in, int num) throws Exception{for (int i = 0; i < num; i++) {System.out.println(in.readLine());}}}}