服务器端

package httpProxyServer;

import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;

public class HttpServer1 {
    private static Map<String,Servlet> servletCache = new HashMap<String,Servlet>(); // 存放Servlet实例的缓存

    public static void main(String[] args) {
        // test，我们先用helloWorld测试一下
        int port;// 定义服务器需要绑定的本地端口号
        ServerSocket serverSocket;// 定义服务器套接口对象

        // 不得不吐槽这异常抛的真不正规
        try {
            port = Integer.getInteger(args[1]);// 将第二个命令行参数转化为整数
        } catch (Exception e) {
            System.out.println("port = 8880 (默认)");
            port = 8880;
        }

        try {
            serverSocket = new ServerSocket(port);
            System.out.println("服务器正在监听端口：" + serverSocket.getLocalPort());

            while (true) {
                try {
                    final Socket socket = serverSocket.accept();
                    System.out.println("建立了与客户的新的TCP连接，该客户的地址为：" + socket.getInetAddress() + ":" + socket.getPort());
                    service(socket);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void service(Socket socket) throws Exception {
        // 读取http请求信息
        InputStream socketIn = socket.getInputStream();// 创建输入流通道
        Thread.sleep(500);
        int size = socketIn.available();// 获取输入流中缓存的大小
        byte[] buffer = new byte[size];// 根据缓存大小在缓存外面建立缓存buffer
        socketIn.read(buffer);// 读取缓存信息到buffer中
        String request = new String(buffer);// 将缓存buffer中的字节放到字符串中
        System.out.println(request);// 输出字符串

        // 解析http请求信息
        String firstLineOfRequest = request.substring(0, request.indexOf("\n\r"));
        String[] parts = firstLineOfRequest.split(" ");
        String uri = parts[1];

        
        if (uri.indexOf("servlet") != -1) {
            // 获取servlet的名字
            String servletName = null;
            if(uri.indexOf("?") != -1)
                servletName = uri.substring(uri.indexOf("servlet/") + 8,uri.indexOf("?"));
            else
                servletName = uri.substring(uri.indexOf("servlet/") + 8,uri.length());
            //尝试从servlet缓存获取servlet对象
            Servlet servlet = (Servlet)servletCache.get(servletName);
            //如果servlet缓存中不存在servlet对象，就创建它，并将它放到servlet缓存中
            if (servlet == null) {
                //这边由于Servlet是抽象接口，必须由子类实现，所以子类必须都要强转为父类
                servlet = (Servlet)Class.forName("servlet." + servletName).newInstance();//这边先简单理解为创建一个对象,动态加载类，和new Servlet()的具体区别请参考反射原理
                servlet.init();
                servletCache.put(servletName, servlet);
            }
            
            //调用Servlet的service()方法
            servlet.service(buffer,socket.getOutputStream());
            
            Thread.sleep(1000);
            socket.close();
            return;//这边有个小细节，如果能找到动态加载的时候，就不需要再执行下面的静态加载方法，直接返回就好
        }
        //....由于演示的是动态加载，为了降低理解难度，静态加载就省略
    }
}

package httpProxyServer;

import java.io.OutputStream;

//这是一个接口类，类中的所有方法都必须在子类中实现
public interface Servlet {

    public void init() throws Exception;

    public void service(byte[] buffer, OutputStream outputStream) throws Exception;

}

package servlet;

import java.io.OutputStream;
import java.io.StreamCorruptedException;

import httpProxyServer.Servlet;

public class HelloServlet implements Servlet {

    @Override
    public void init() throws Exception {
        System.out.println("这边是servlet的初始化!");
    }

    @Override
    public void service(byte[] buffer, OutputStream outputStream) throws Exception {
        String request = new String(buffer);
        //获取http请求的第一行
        String firstLineOfReqest = request.substring(0,request.indexOf("\r\n"));
        //解析http请求的第一行
        String[] parts = firstLineOfReqest.split(" ");
        String method = parts[0];
        String uri = parts[1];
        String username = null;
        //如果请求方式为get
        if(method.equalsIgnoreCase("get") && uri.indexOf("username=") != -1){
            String parameters = uri.substring(uri.indexOf("?"),uri.length());
            parts = parameters.split("&");
            parts = parts[0].split("=");
            username = parts[1];
        }
        //如果请求方式为post
        if (method.equalsIgnoreCase("post")) {
            int locate = request.indexOf("\r\n\r\n");
            //获得响应正文
            String content = request.substring(locate+4,request.length());
            if(content.indexOf("username") != -1){
                parts = content.split("&");
                parts = parts[0].split("=");
                username = parts[1];
            }
        }
        
        //创建并发送http响应
        outputStream.write("HTTP/1.1 200 OK\r\n".getBytes());//响应首部
        outputStream.write("Content-type: text/html\r\n\r\n".getBytes());//响应头
        outputStream.write("<html><head><title>HelloWorld</title></head><body>".getBytes());
        outputStream.write(new String("<h1>Hello:"+username+"</h1></body></html>").getBytes());
    }
}

客户端

package httpProxyServer;

import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

public class HttpClient1 {

    public static void main(String[] args) {
        //相比较于静态客户端，这边uri变了，servlet是给服务器去判断是不是需要通过servlet类动态加载资源，/后面是要求处理业务的具体的servlet子类
        String uri = "servlet/HelloServlet";
        if(args.length != 0) uri=args[0];//这边需要区别c语言下的参数，这边的第一个参数是不包括命令行自身的。
        doGet("localhost",8880,uri);
    }

    private static void doGet(String host, int port, String uri) {
        Socket socket = null;
        try {
            socket = new Socket(host,port);
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        try {
            //创建http请求
            StringBuffer sb = new StringBuffer("GET " + uri + " HTTP/1.1\r\n");
            sb.append("Accept: */*\r\n");
            sb.append("Accept-Encoding: gzip,deflate\r\n");
            sb.append("Accept-Language: zh-cn\r\n");
            sb.append("User-Agent: HTTPClient\r\n");
            sb.append("Connection: Keep-Alive\r\n\r\n");
            
            //发送http请求
            OutputStream socketOut = socket.getOutputStream();
            socketOut.write(sb.toString().getBytes());
            Thread.sleep(2000);
            
            //接收响应结果
            InputStream socketIn = socket.getInputStream();
            int size = socketIn.available();
            byte[] buffer = new byte[size];
            socketIn.read(buffer);
            System.out.println(new String(buffer));
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                socket.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}