MyServer

 //一、设置一个8089端口的本地IP服务器
 1 package myserver;

 import java.io.IOException;
 import java.net.ServerSocket;
 import java.net.Socket;

 public class MyServer {
     public MyServer() {
         try {
             ServerSocket socket = new ServerSocket(8089);
             while (true) {
                 Socket s = socket.accept();
                 new SocketThread(s);
             }
         } catch (IOException e) {
             e.printStackTrace();
         }
     }
     public static void main(String[] args) {
         new MyServer();
     }
 }

 //二、多线程监听客户端连接
 1 package myserver;

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

 public class SocketThread implements Runnable{
     private Socket socket;

     public SocketThread(Socket socket) {
         this.socket = socket;

         Thread th = new Thread(this);
         th.start();
     }

     @Override
     public void run() {
         InputStream in = null;
         OutputStream out = null;
         try {
             in = socket.getInputStream();//获取文件读取流
             out = socket.getOutputStream();//获取文件写入流
             Response response = new Response(out);//相应数据到浏览器
             Request request = new Request(in);//从网页获取数据
             System.out.println("********"+request);
             String url = request.getUrl();//获取URL路径
             //response.sendMessage("hello");
             response.sendFile(url);
             out.flush();
         } catch (IOException e) {
             e.printStackTrace();
         }finally{
             try {
                 out.close();
                 in.close();
                 socket.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
     }
 }

 //三、请求相应处理
 1 package myserver;

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;

 public class Response {
     private OutputStream out;

     public Response(OutputStream out) {
         this.out = out;
     }

     //发送消息到浏览器
     public void sendMessage(String msg) {
         try {
             out.write(msg.getBytes());
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

     public void sendFile(String filePath) throws IOException {
         File f = new File(filePath);
         if (f.exists() == false) {//判断文件是否存在
             return;
         }
         InputStream in = null;
         try {
             in = new FileInputStream(filePath);
             byte[] by = new byte[1024];
             int len = 0;
             while ((len=in.read(by)) != -1) {
                 out.write(by, 0, len);//读取1024字节并写入到浏览器
             }
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         }finally{
             in.close();
         }
     }
 }

//接受客户端请求
 1 package myserver;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.HashMap;
 import java.util.Map;

 public class Request {
     private String url;
     //封装表单数据
     private Map<String,String> paramMap = new HashMap<String,String>();

     public Request(InputStream in) {
         byte[] by = new byte[1024];
         try {
             in.read(by);
             String str = new String(by).trim();//去掉两边空格
             System.out.println(str);

             if (str.startsWith("GET")){//GET开头的流数据
                 this.getGet(str);
             }else{//POST开头的流数据
                 this.getPOST(str);
             }
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

     private void getPOST(String str) {//获取POST的URL和表单数据
         String[] s = str.split("\\s+");//按空格割分字符串为字符串数组
         this.url = s[1].substring(1);//表单的POST提交
         getMap(s[s.length-1]);//获取表单数据
     }

     private void getGet(String str) {//获取GET的URL和表单数据
         String[] s = str.split("\\s+");//按空格割分字符串为字符串数组
         if (s[1].indexOf("?") == -1){
             this.url = s[1].substring(1);//文本的GET提交
         }else{
             String s1 = s[1];
             //表单的GET提交
             this.url = s1.split("[?]")[0].substring(1);
             this.getMap(s1.split("[?]")[1]);//获取表单数据
         }
     }
     //GET /url    POST|GET /url?userName=""&pwd=""&age=""&sex=""
     private Map<String,String> getMap(String string) {//获取表单数据
         String[] s = string.split("[&]");
         for (String str : s) {
             this.paramMap.put(str.split("[=]")[0], str.split("[=]")[1]);
         }
         return this.paramMap;
     }

     public String getUrl() {
         return this.url;
     }

     @Override
     public String toString() {
         return "Request [url=" + url + ", paramMap=" + paramMap + "]";
     }
 }

 //模拟GET，POST请求表单提交的登录界面
 1 <!DOCTYPE html>
 <html>
 <head>
 <meta charset="UTF-8">
 <title>login</title>
 </head>
 <body>
     <img alt="" src="1.jpg" width="300" height="200"/><br/>
     <img alt="" src="1.jpg" width="300" height="200"/><br/>
     <p>智商不够，努力来凑</p>

     <form action="login" method="PUT">
         <input type="text" name="userName"><br/>
         <input type="password" name="pwd"><br/>
         <input type="submit" value="登录">
     </form>
 </body>
 </html>

相应的数据流信息如下：

GET /login.html HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Accept-Language: zh-CN
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=login.html, paramMap={}]

GET /1.jpg HTTP/1.1
Accept: */*
Referer: http://localhost:8089/login.html
Accept-Language: zh-CN
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=1.jpg, paramMap={}]

GET /login?userName=123&pwd=123 HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Referer: http://localhost:8089/login.html
Accept-Language: zh-CN
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=login, paramMap={userName=123, pwd=123}]

GET /login?userName=123&pwd=123 HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Accept-Language: zh-CN
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=login, paramMap={userName=123, pwd=123}]

GET /a.txt HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Accept-Language: zh-CN
Cache-Control: no-cache
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=a.txt, paramMap={}]

GET /1.jpg HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Accept-Language: zh-CN
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=1.jpg, paramMap={}]

GET / HTTP/1.1
Accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, */*
Accept-Language: zh-CN
Cache-Control: no-cache
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
Host: localhost:8089
Connection: Keep-Alive
********Request [url=, paramMap={}]

总结：以上是用代码模拟实现的一个tomcat。