因为对java的network programmiing不太了解，所以就试着写个simple proxy server练练手。
虽然问题很多，而且处理简直就可以说是“没有处理”。但是，还是可以通过这个代理浏览网页，并且统计有多少流量流出和流入。代码如下。（这篇帖子就是同个这个proxy发的）。
1. 将serverSocket.close()改成if (serverSocket!=null) serverSocket.close();后，异常打印少了很多。没有null pointer exception了。
2. 将第一次从浏览器读取的request的count进行判断，如果<=0，就直接关掉socket；如果大于0，才进行其他处理。浏览网页速度变快了。不知道为什么。
package network.proxy;import java.io.*;import java.net.*;import java.util.*;// internet server <--serverSocket--> proxy <--clientSocket--> client public class MyProxy { public static void main(String[] args) { try { new Thread(new SimpleProxyServer(8989)).start(); } catch (IOException e) { e.printStackTrace(); } }}class SimpleProxyServer implements Runnable { private ServerSocket listenSocket; public SimpleProxyServer(int port) throws IOException { this.listenSocket = new ServerSocket(port); } public void run() { for (;;) { try { Socket clientSocket = listenSocket.accept(); System.out.println("Create a new Thread to handle this connection"); new Thread(new ConnectionHandler(clientSocket)).start(); } catch (IOException e) { e.printStackTrace(); } } }}class ProxyCounter { static int sendLen = 0; static int recvLen = 0; public static void showStatistics() { System.out.println("sendLen = " + sendLen); System.out.println("recvLen = " + recvLen); }}// must close sockets after a transaction class ConnectionHandler extends ProxyCounter implements Runnable { private Socket clientSocket; private Socket serverSocket; private static final int bufferlen = 8192; public ConnectionHandler(Socket clientSocket) { this.clientSocket = clientSocket; } public void run() { // receive request from clientSocket, //extract hostname, //create a serverSocket to communicate with the host // count the bytes sent and received try { byte[] buffer = new byte[bufferlen]; int count = 0; InputStream inFromClient = clientSocket.getInputStream(); count = inFromClient.read(buffer); String request = new String(buffer, 0, count); String host = extractHost(request); // create serverSocket Socket serverSocket = new Socket(host, 80); // forward request to internet host OutputStream outToHost = serverSocket.getOutputStream(); outToHost.write(buffer, 0, count); outToHost.flush(); sendLen += count; showStatistics(); // forward response from internet host to client InputStream inFromHost = serverSocket.getInputStream(); OutputStream outToClient = clientSocket.getOutputStream(); while (true) { count = inFromHost.read(buffer); if (count < 0) break; outToClient.write(buffer, 0, count); outToClient.flush(); recvLen += count; showStatistics(); } } catch (IOException e) { e.printStackTrace(); } finally { try { clientSocket.close(); serverSocket.close(); } catch (IOException e) { e.printStackTrace(); } } } private String extractHost(String request) { int start = request.indexOf("Host: ") + 6; int end = request.indexOf('\n', start); String host = request.substring(start, end - 1); return host; }}