深入剖析Tomcat-手写简单的HTTP服务器

首先需要了解HTTP请求和响应

1.1 HTTP请求

一个HTTP请求包含3个部分：

1. 请求方法（GET/POST/DELETE等） 统一资源标识符（URI） 协议/版本（HTTP/1.1）
2. 请求头（Key-value）
3. 实体

1.2 HTTP响应

一个HTTP响应也包含3个部分

1. 协议（HTTP/1.1） 状态码（200/404/500等） 描述（OK）
2. 响应头（K-V）
3. 响应实体段

2.1 Java网络编程的两个类

Java中的网络编程主要用到的类有Socket（客户端）和ServerSocket（服务端）两个。
客户端主要是通过Socket向服务端发送请求。
服务端主要是在监听客户端发送的请求并处理请求，因此服务端需要一值保持监听状态。服务端从来不会主动向客户端发送请求。

3.1应用程序实现

主要有3个类：

Request 客户端

Response 服务端

HttpServer 主程序

package ex01.lqp;

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

/**
 * Created by lqp
 * Date: 2019/6/12
 */
public class Request {
    
    
    private InputStream input;
    private String uri;

    public Request(InputStream input)
    {
    
    
        this.input = input;
    }

    public void parse(){
    
    
        //从socket中读取一系列字符

        StringBuffer request = new StringBuffer(2048);
        int i;
        byte[] buffer = new byte[2048];
        try{
    
    
            i = input.read(buffer);
        }catch (IOException e){
    
    
            e.printStackTrace();
            i=-1;
        }
        for(int j=0;j<i;j++)
        {
    
    
            request.append((char)buffer[j]);
        }
        System.out.println(request.toString());
        uri = parseUri(request.toString());
    }

    public String parseUri(String requestString){
    
    
        int index1,index2;
        index1 = requestString.indexOf(' ');
        if(index1!=-1)
        {
    
    
            index2 = requestString.indexOf(' ',index1+1);
            if(index2>index1)
            {
    
    
                return requestString.substring(index1+1,index2);
            }
        }
        return null;
    }

    public String getUri()
    {
    
    
        return uri;
    }

}

package ex01.lqp;

import java.io.*;

/**
 * Created by lqp
 * Date: 2019/6/12
 */
public class Response {
    
    
    private static final int BUFFER_SIZE = 1024;
    Request request;
    OutputStream output;
    public Response(OutputStream output)
    {
    
    
        this.output = output;
    }

    public void setRequest(Request request)
    {
    
    
        this.request = request;
    }

    public void sendStaticResource() throws IOException {
    
    
        byte[] bytes = new byte[BUFFER_SIZE];
        FileInputStream fis = null;
        try{
    
    
            File file = new File(HttpServer.WEB_ROOT,request.getUri());
            if(file.exists()){
    
    
                fis = new FileInputStream(file);
                int ch = fis.read(bytes,0, BUFFER_SIZE);
                while(ch!=-1)
                {
    
    
                    output.write(bytes,0,ch);
                    ch = fis.read(bytes,0,BUFFER_SIZE);
                }
            }
            else{
    
    
                //file not find
                String errorMessage = "HTTP/1.1 404 File Not Found\r\n"+
                        "Content-Type: text/html\r\n"+
                        "Content-Length: 23\r\n"+
                        "\r\n"+
                        "<h1>File Not Found</h1>";
                output.write(errorMessage.getBytes());
            }
        }catch (Exception e){
    
    
            System.out.println(e.toString());

        }
        finally {
    
    
            if(fis!=null)
            {
    
    
                fis.close();
            }
        }
    }

}

package ex01.lqp;

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

/**
 * Created by lqp
 * Date: 2019/6/12
 */
public class HttpServer {
    
    
    public static final String WEB_ROOT = System.getProperty("user.dir")+ File.separator+"webroot";

    //shutdown command
    private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

    //the shutdown command recived
    private boolean shutdown = false;

    public static void main(String[] args)
    {
    
    
        HttpServer server = new HttpServer();
        server.await();
    }

    public void await()
    {
    
    
        ServerSocket serverSocket = null;
        int port = 8080;
        try{
    
    
            serverSocket = new ServerSocket(port,1, InetAddress.getByName("127.0.0.1"));
        }catch (IOException e)
        {
    
    
            e.printStackTrace();
            System.exit(1);
        }

        //Loop waiting for a request
        while(!shutdown)
        {
    
    
            Socket socket = null;
            InputStream input=null;
            OutputStream output = null;
            try{
    
    
                socket = serverSocket.accept();
                input = socket.getInputStream();
                output = socket.getOutputStream();

                //创建Request对象并解析
                Request request = new Request(input);
                request.parse();

                //创建Response对象
                Response response = new Response(output);
                response.setRequest(request);
                response.sendStaticResource();

                socket.close();

                shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
            }catch (Exception e)
            {
    
    
                e.printStackTrace();
                continue;
            }
        }

    }

}

运行程序：
启动Main函数后，在浏览器中输入：
http://localhost:8080/filename 即可在控制台看到请求以及响应。

该程序通过 SHUTDOWN命令关闭，因此在浏览器中输入一下地址即可关闭程序：
http://localhost:8080/SHUTDOWN