how tomcat works 读书笔记(一)----------一个简单的web服务器

http协议

若是两个人能正常的说话交流,那么他们间必定有一套统一的语言规则<在网络上服务器与客户端能交流也依赖与一套规则,它就是我们说的http规则(超文本传输协议Hypertext transfer protocol)。
http分两部分,一个是请求(客户端发给服务器),一个是回复(服务器发给客户端)。
先看http请求 

下面就是一个http请求的例子,其中的各项参数,请查阅相关资料。(http://www.cnblogs.com/yin-jingyu/archive/2011/08/01/2123548.html)

http回复

下面就是http回复的例子,除了这个图之外,后面的部分就是大家看到的页面的源代码

socket

我们一般说的socket,广义上包含java.net包下的Socket类与ServerSocekt类。
另一方面有基于tcp的网络编程也有基于udp的网络编程,其中差别大家百度,这里只谈tcp。
定义性的东西大家可以查看各种资料(个人推荐尚学堂 马士兵老师讲解的socket部分视频,但在看socket之前建议大家先看io部分),带大家看一段代码,大家应该就会知道socket编程的大致原理了。(代码来自马士兵老师的讲义)

import java.net.*;
import java.io.*;


public class TCPServer {
	public static void main(String[] args) throws Exception {
		ServerSocket ss = new ServerSocket(6666);      //在本机的TCP6666号端口上监听
		while(true) {
			Socket s = ss.accept();                //ServerSocket的accept为阻塞式方法,只有当它监听到一个请求时
			                                       //它才会执行
                        System.out.println("a client connect!");
			DataInputStream dis = new DataInputStream(s.getInputStream());//获得客户端向自己说的"话"
			                                       //InputStream 从外部指向内存
			System.out.println(dis.readUTF());     //按照uft-8的格式读取内容
			dis.close();
			s.close();
		}
		
	}
}


import java.net.*;
import java.io.*;


public class TCPClient {
	public static void main(String[] args) throws Exception {
		Socket s = new Socket("127.0.0.1", 6666);       //连接127.0.0.1(本机)的tcp端口6666
		OutputStream os = s.getOutputStream();          //获得一条线路,来给服务器"说话"
		DataOutputStream dos = new DataOutputStream(os);//对这个线路进行包装
		Thread.sleep(3000);                             //"暂停"3秒
		dos.writeUTF("hello server!");                  //对服务器说 hello server! 
		dos.flush();
		dos.close();
		s.close();
	}
}

先运行server端,再运行client端。当运行client端后,控制台首先会打印a client connect!三秒之后会打印hello server! 

模拟一个最最最基础的tomcat

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


public class HttpServer {


  /** WEB_ROOT is the directory where our HTML and other files reside.
   *  For this package, WEB_ROOT is the "webroot" directory under the working
   *  directory.
   *  The working directory is the location in the file system
   *  from where the java command was invoked.
   */
  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 received
  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"));  
                //这个1是什么功能 参加 http://www.51cto.com/art/200702/40196_1.htm
    }
    catch (IOException e) {
      e.printStackTrace();
      System.exit(1);
    }


    // Loop waiting for a request
    while (!shutdown) {  //最开始的时候 shutdown为false 这段话会执行
      Socket socket = null;
      InputStream input = null;
      OutputStream output = null;
      try {
        socket = serverSocket.accept();   //只有当有客户端请求时 它才会运行 阻塞式方法!
        System.out.println(new Date()+"AAAAAAAAAAAA");
        input = socket.getInputStream();  //里面放的是客户端对服务器说的话
        output = socket.getOutputStream();//这里面将要放的是服务器要对客户端说的话


        // create Request object and parse
        Request request = new Request(input);
        request.parse();                  //参见request


        // create Response object
        Response response = new Response(output);
        response.setRequest(request);
        response.sendStaticResource();


        // Close the socket
        socket.close();


        //check if the previous URI is a shutdown command
        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
      }
      catch (Exception e) {
        e.printStackTrace();
        continue;
      }
    }
  }
}

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


public class Request {


  private InputStream input;
  private String uri;


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


  public void parse() {
    // Read a set of characters from the socket
    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]);   //将客户端的请求加到request(StringBuffer)中
    }
    System.out.println("request 如下");
    System.out.print(request.toString());
    uri = parseUri(request.toString());
    System.out.println("uri 如下  "+uri);
  }


  /**
  *看看System.out.println("uri 如下  "+uri); 就不用解释这个方法了
  *
  **/
  private 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;
  }


}

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


/*
  HTTP Response = Status-Line
    *(( general-header | response-header | entity-header ) CRLF)
    CRLF
    [ message-body ]
    Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
*/


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 {
      System.out.println(HttpServer.WEB_ROOT+"  **** "+request.getUri());
      File file = new File(HttpServer.WEB_ROOT, request.getUri());   //连接用户请求的"文件"
      if (file.exists()) {
        fis = new FileInputStream(file);
        int ch = fis.read(bytes, 0, BUFFER_SIZE);       //把文件里的东西读出来放到bytes字符数组里
        while (ch!=-1) {                                //把bytes数组里的东西放到要给客户端回复的流里面
          output.write(bytes, 0, ch);
          ch = fis.read(bytes, 0, BUFFER_SIZE);
        }
      }
      else {                                            //要是文件不存在  不解释
        // file not found
        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) {
      // thrown if cannot instantiate a File object
      System.out.println(e.toString() );
    }
    finally {
      if (fis!=null)
        fis.close();
    }
  }
}

首先如果大家用的是Eclipse,那么没有任何问题,如果大家是用命令行的形式的话会存在一个问题,HttpServer与Response两个类相互依赖,先编译谁?
解决办法 cd到三个类的目录 然后 javac *.java


等启动HttpServer后
在浏览器输入localhost:8080/index.html

显示如下 

明白了吧 我们把index.html放到D:\尚学堂 j2ee\javase\尚学堂科技_马士兵_J2SE_5.0_第01章_JAVA简介_源代码_及重要说明\java\Socket\no\WebContent 目录下

index.html内容如下
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
我是index
</body>
</html>

再次请求 截图如下

大家一定很奇怪,我为什么不用火狐或这个Chrome,找个EditPlus点过来点过去。
大家试试就知道了,火狐不知道因为什么原因,在地址栏敲回车后,会发出两次请求。结果就是报错。

再试试http://localhost:8080/SHUTDOWN

程序退出