一直以来都在使用Tomcat作为servlet容器，很好奇tomcat的工作原理和结构。正好How tomcat works这本书讲解的比较清晰，虽然很多东西不懂，但也要慢慢来研究一下，这样才能有提高。

tomcat中最核心的部分是catalina,我们可以将其简单的看做由两个主要模块构成的，连接器connector和容器container,他们之间的对应关系如下

连接器负责为接收到得每个http请求构造一个resquest和response对象，然后传递给container，容器负责调用servlet的service方法。

下面就创建一个最简单的基于java的web服务器来响应请求。该服务器只能处理静态的资源请求。

一个基于java的web服务器要涉及到两个非常重要的类，socket和server socket,通过http协议进行通讯。

下面是一个HttpServer类

package server1;

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;
import java.net.UnknownHostException;

public class HttpServer {
	private boolean shutdown = false;//服务器是否停止
	public static String WEB_ROOT = System.getProperty("user.dir") + File.separator  + "webroot";//服务器资源目录
	public static void main(String[] args) {
		System.out.println(WEB_ROOT);
		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 (UnknownHostException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		Socket socket = null;
		InputStream input = null;
		OutputStream output = null;
		while(!shutdown){//不停的接受请求
			try {
				socket = serverSocket.accept();
				input = socket.getInputStream();
				output = socket.getOutputStream();
			} catch (IOException e) {
				e.printStackTrace();
			}
			Request request = new Request(input);
			request.parse();//解析url
			Response response = new Response(output);
			response.setRequest(request);
			try {
				response.sendStaticResource();//返回客户端
				socket.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		
	}
}

下面是Request类

package server1;

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

public class Request {
	private InputStream input;
	private String uri;
	public String getUri() {
		return uri;
	}
	public void setUri(String uri) {
		this.uri = uri;
	}
	public Request(InputStream input){
		this.input = input;
	}
	//读取客户端的请求，并解析出uri
	public void parse(){
		StringBuffer request = new StringBuffer(2048);
		int i = 0;
		byte[] buffer = new byte[2048];
		try {
			i = input.read(buffer);
		} catch (IOException e) {
			e.printStackTrace();
		}
		for(int j=0;j<i;j++){
			request.append((char)buffer[j]);
		}
		System.out.println(request.toString());
		uri = this.parseUri(request.toString());
		System.out.println(uri);
	}
	//传入的requestString类似以GET /favicon.ico HTTP/1.1开头
	//该方法负责将uri截取出来
	public String parseUri(String requestString){
		int index1,index2;
		index1 = requestString.indexOf(" ");
		if(index1!=-1){
			index2 = requestString.indexOf(" ", index1+1);
			if(index2!=-1){
				return requestString.substring(index1+1, index2);
			}
		}
		return null;
	}
	
}

下面是Response类

package server1;

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

public class Response {
	private OutputStream output;
	Request request;
	private static final int  BUFFER_SIZE = 1024;
	public void setRequest(Request request) {
		this.request = request;
	}
	public Response(OutputStream output){
		this.output =  output;
	}
	public void sendStaticResource() throws IOException{
		byte[] bytes = new byte[BUFFER_SIZE];
		FileInputStream fis = null;
		try {
			File file = new File(HttpServer.WEB_ROOT,request.getUri());
			//判断资源目录下是否有此页面，有的话输出到客户端
			if(file.exists()){
			
				fis = new FileInputStream(file);
				int i = fis.read(bytes);
				while(i!=-1){
					output.write(bytes, 0, i);
					i = fis.read(bytes);
				}
			}else {
				// 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) {
				e.printStackTrace();
		}finally{
			if(fis!=null)
				fis.close();
		}
				
	}
}

在浏览器中访问 http://localhost:8080/index.html即可。在工程的根目录建立webroot文件夹添加index.html即可访问到