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杂谈socket编程

作者：xcbeyond
疯狂源自梦想，技术成就辉煌！微信公众号：《程序猿技术大咖》号主，专注后端开发多年，拥有丰富的研发经验，乐于技术输出、分享，现阶段从事微服务架构项目的研发工作，涉及架构设计、技术选型、业务研发等工作。对于Java、微服务、数据库、Docker有深入了解，并有大量的调优经验。

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();
       }
       @Override
       public 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;
       }
       @Override
       public 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，filename
                       saveFile(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());
           }
       }

   }
}

JAVA