How Tomcat Works 读书笔记（一）

一直以来觉得容器都是一个很神秘的东西，一般开发的时候不会关心容器到底是怎么实现的。现在看了《How Tomcat Works》这本书后大概知道容器的实现，写出来自己巩固下
java 基础里面有章是关于Socket的，这个对象是通过http协议来发送消息的。tomcat既然是通过JAVA来实现他的底层也是通过Socket来实现。
首先实现一个Servlet容器。它的功能是可以加载serlvet对象以及访问静态文件。
1、Server端

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;

public class MockServer {
	public static final String  = System.getProperty("user.dir") + File.separator + "webroot";

	private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

	private boolean shutdown = false;

	public static void main(final String[] args) throws Exception {
		MockServer server = new MockServer();
		server.await();
	}

	public void await() {
		ServerSocket socketServer = null;
		int port = 8080;
		try {
			socketServer = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
		} catch (IOException e) {
			e.printStackTrace();
		}
		while (!shutdown) {
			Socket socket = null;
			InputStream in = null;
			OutputStream out = null;
			try {
				socket = socketServer.accept();
				in = socket.getInputStream();
				out = socket.getOutputStream();
				Request request = new Request(in);
				request.parse();
				Response response = new Response(out);
				response.setRequest(request);
				socket.close();
				if (request.getUri().startsWith("/servlet")) {
					MockServletPorcessor servlet = new MockServletPorcessor();
					servlet.process(request, response);
				} else if (request.getUri().equals(SHUTDOWN_COMMAND)) {
					shutdown = true;
				} else {
					StaticResource sr = new StaticResource();
					sr.process(request, response);
				}
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		}
	}

}

代码很简单前面就是启动一个server并且接受socket 后面解释下request.getUri()这个方法后面会说，就是截取"GET /XXXX HTTP/1.1"HTTP协议的字符串，如果我们的请求是http://127.0.0.1:8080/SHUTDOWN 截取后的结果就是SHUTDOWN。

2、Request对象

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;

public class Request implements ServletRequest {

	private final InputStream in;

	private String uri;

	public Request(final InputStream in) {
		this.in = in;
	}

	public void parse() {
		StringBuffer sb = new StringBuffer(2048);
		int i = 0;
		byte[] buffer = new byte[2048];
		try {
			i = in.read(buffer);
		} catch (IOException e) {
			e.printStackTrace();
		}
		for (int j = 0; j < i; j++) {
			sb.append((char) buffer[j]);
		}
		System.out.println(String.valueOf(sb));
		uri = parseUri(String.valueOf(sb));

	}

	// "GET /SHUTDOWN HTTP/1.1"
	private String parseUri(final String request) {
		int index1, index2;
		index1 = request.indexOf(' ');
		if (index1 != -1) {
			index2 = request.indexOf(' ', index1 + 1);
			if (index2 > index1) {
				return request.substring(index1 + 1, index2);
			}
		}
		return null;
	}

	public String getUri() {
		return uri;
	}

	@Override
	public Object getAttribute(final String arg0) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public Enumeration getAttributeNames() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getCharacterEncoding() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public int getContentLength() {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public String getContentType() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public ServletInputStream getInputStream() throws IOException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getLocalAddr() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getLocalName() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public int getLocalPort() {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public Locale getLocale() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public Enumeration getLocales() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getParameter(final String arg0) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public Map getParameterMap() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public Enumeration getParameterNames() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String[] getParameterValues(final String arg0) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getProtocol() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public BufferedReader getReader() throws IOException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getRealPath(final String arg0) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getRemoteAddr() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getRemoteHost() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public int getRemotePort() {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public RequestDispatcher getRequestDispatcher(final String arg0) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getScheme() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getServerName() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public int getServerPort() {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public boolean isSecure() {
		// TODO Auto-generated method stub
		return false;
	}

	@Override
	public void removeAttribute(final String arg0) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setAttribute(final String arg0, final Object arg1) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setCharacterEncoding(final String arg0) throws UnsupportedEncodingException {
		// TODO Auto-generated method stub

	}

}

自己定义的request对象 这个对象由于是基因servlet实现所以必须实现ServletRequest的方法。具体的servlet方法现在都没实现，暂时只实现一个截取uri的方法。这个方法的作用前面已经说明。

3、Response方法

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Locale;

import javax.servlet.ServletOutputStream;
import javax.servlet.ServletResponse;

public class Response implements ServletResponse {

	private static final int BUFFER_SIZE = 1024;
	private Request request;
	private final OutputStream out;
	private PrintWriter writer;

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

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

	public void sendStaticResource() {
		byte[] bytes = new byte[BUFFER_SIZE];
		FileInputStream fis = null;
		try {
			File file = new File(MockServer.WEB_ROOT, request.getUri());

			if (file.exists()) {
				fis = new FileInputStream(file);
				int ch = fis.read(bytes, 0, BUFFER_SIZE);
				while (ch != -1) {
					out.write(bytes, 0, ch);
					ch = fis.read(bytes, 0, BUFFER_SIZE);
				}
			} else {
				String message = "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>";
				out.write(message.getBytes());
			}

		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			if (null != fis) {
				try {
					fis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

	@Override
	public void flushBuffer() throws IOException {
		// TODO Auto-generated method stub

	}

	@Override
	public int getBufferSize() {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public String getCharacterEncoding() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getContentType() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public Locale getLocale() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public ServletOutputStream getOutputStream() throws IOException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public PrintWriter getWriter() throws IOException {
		writer = new PrintWriter(out, true);
		return writer;
	}

	@Override
	public boolean isCommitted() {
		// TODO Auto-generated method stub
		return false;
	}

	@Override
	public void reset() {
		// TODO Auto-generated method stub

	}

	@Override
	public void resetBuffer() {
		// TODO Auto-generated method stub

	}

	@Override
	public void setBufferSize(final int arg0) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setCharacterEncoding(final String arg0) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setContentLength(final int arg0) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setContentType(final String arg0) {
		// TODO Auto-generated method stub

	}

	@Override
	public void setLocale(final Locale arg0) {
		// TODO Auto-generated method stub

	}
}

也是实现servlet的接口，同时实现一个sendStaticResource（）这个方法就是访问静态文件，如果不能访问就返回404错误。

4、MockServletPorcessor
这个方法就是对servlet的处理类，如果请求的后缀有/servlet那么代码就会进入这个类

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLStreamHandler;

import javax.servlet.Servlet;

public class MockServletPorcessor {

	public void process(final Request request, final Response response) {

		String uri = request.getUri();
		String servletName = uri.substring(uri.lastIndexOf("/") + 1);
		URLClassLoader loader = null;
		try {
			URL[] urls = new URL[1];
			URLStreamHandler handler = null;
			File = new File("bin/com/xxx/server");
			String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString();
			System.out.print(repository);
			urls[0] = new URL(null, repository, handler);
			loader = new URLClassLoader(urls);
			Class myClass = loader.loadClass(servletName);
			Servlet servlet = (Servlet) myClass.newInstance();
			servlet.service(request, response);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		// TODO Auto-generated method stub

	}

}

这个类的基本功能有3个
(1)加载servlet类库
classpath的路径是servlet的路径（bin/com/xxx/server）
(2)加载servlet类
(3)实现service方法

5、StaticResource静态访问类

public class StaticResource {

	public void process(final Request request, final Response response) {

		response.sendStaticResource();
	}

}

只是简单的调用response类。

6、TestServlet

package com.xxx.server;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class TestServlet implements Servlet {

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}

	@Override
	public ServletConfig getServletConfig() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getServletInfo() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void init(final ServletConfig arg0) throws ServletException {
		// TODO Auto-generated method stub

	}

	@Override
	public void service(final ServletRequest request, final ServletResponse response) throws ServletException,
			IOException {
		System.out.println("In Service");
	}

}

一个简单的serlvet 这里保留了包的名称因为以后会说到

启动server容器 然后我们可以通过页面上
http://127.0.0.1:8080/servlet/com.xxx.server.TestServlet 这里必须使用全限定名才行
来运行servlet
通过http://127.0.0.1:8080/index.html来访问资源(当然前提是WEB_ROOT下面有这个资源)
通过http://127.0.0.1:8080/SHUTDOWN来关闭容器