<h3>最近复习计算机网络，复习完应用层之后对于理论知识还是没有一个深刻的概念，索性就动手用Java Socket API 模拟做一个HTTP服务器，巩固一下应用层的知识。</h3>
<blockquote>
HTTP基于TCP协议，协议采用了请求/响应模型。客户端向服务器发送一个请求，请求头包含请求的方法、URL、协议版本、以及包含请求修饰符、客户信息和内容的类似于MIME的消息结构。服务器以一个状态行作为响应，响应的内容包括消息协议的版本，成功或者错误编码加上包含服务器信息、实体元信息以及可能的实体内容——百度百科。

话不多说，还是直接上图。
</blockquote>

http.png

具体字段这里不作解释，不懂的请先自己了解http协议。这里主要是根据请求响应这一过程模拟HTTP服务器。
下面是代码：
<pre>

package com.example.httpserver;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class HttpServer {
    private static final Integer port = 80;//HTTP默认端口80
    
    public static void main(String[] args) {
        ServerSocket serverSocket;
        
        try {
            //建立服务器Socket,监听客户端请求
            serverSocket = new ServerSocket(port);
            System.out.println("Server is running on port:"+serverSocket.getLocalPort());
            //死循环不间断监听客户端请求
            while(true){
                final Socket socket = serverSocket.accept();
                System.out.println("biuld a new tcp link with client,the cient address:"+  
                        socket.getInetAddress()+":"+socket.getPort());
                //并发处理HTTP客户端请求
                service(socket);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    public static void service(Socket socket)
    {
        new Thread(){
            public void run(){
                InputStream inSocket;
                try {
                    //获取HTTP请求头
                    inSocket = socket.getInputStream();
                    int size = inSocket.available();
                    byte[] buffer = new byte[size];
                    inSocket.read(buffer);
                    String request = new String(buffer);
                    System.out.println("ClientBrowser:\n"+request+"\n"
                            + "------------------------------------------------------------------");
                    
                    String firstLineOfRequest = "";
                    String[] heads;
                    String uri = "/index.html";
                    String contentType ="";
                    if(request.length() > 0){
                        firstLineOfRequest = request.substring(0,request.indexOf("\r\n"));
                        heads = firstLineOfRequest.split(" ");
                        uri = heads[1];
                        
                        if(uri.indexOf("html") != -1){
                            contentType = "text/html";
                        }else{
                            contentType = "application/octet-stream";
                        }
                    }
                    //将响应头发送给客户端
                    String responseFirstLine = "HTTP/1.1 200 OK\r\n";
                    
                    String responseHead = "Content-Type:" + contentType +"\r\n";
                    
                    OutputStream outSocket = socket.getOutputStream();
                    System.out.println("ServerResponse:\n"+responseFirstLine+"\n"+responseHead+"\n"
                            + "--------------------------------------------------------------------");
                    outSocket.write(responseFirstLine.getBytes());
                    outSocket.write(responseHead.getBytes());
                    //通过HTTP请求中的uri读取相应文件发送给客户端
                    FileInputStream writehtml = new FileInputStream(new File("wwwroot"+uri));
                    outSocket.write("\r\n".getBytes());  
                    byte[] htmlbuffer = new byte[writehtml.available()];
                    if(writehtml !=null){
                        int len = 0;
                        System.out.println("writeHtml");
                        while((len = writehtml.read(htmlbuffer)) != -1){
                            outSocket.write(htmlbuffer, 0,len);
                        }
                    }
                    outSocket.close();
                    socket.close();
                
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }

}

</pre>

代码看注释也很容易理解。现在我们在浏览器中输入服务器地址+要访问的文件

request.png

在看我们控制台输出的内容：

response.png

<h5>以上就是Java Socket 简单的模拟HTTP服务器全过程。</h5>