How Tomcat Works 2: A Simple Servlet Server

1 javax.servlet.Servlet 接口

（1）接口包含五个方法：

Public void init(ServletCongig config)

Public void service(ServletRequest request, ServletResponse response)

Public void destory()

Public void ServletConfig getServletConfig()

Public String getServletInfo()

（2）方法解析：

    Init(),service(),destory()是servlet的生命周期方法。

    init()： Servlet Container在实例化servlet类时，会调用init(), 仅调用一次，可以用加载data driver, 初始化值等功能override这个方法。

    service(): 每次有request for servlet都会调用service()方法，传入request 信息，处理数据，封装response信息。

    destory(): 当从servlet container移除serlvet实例时，调用destroy()。通常SHUTDOWN或者servlet container 需要更多内存时，会调用该方法。

  （3）实现类实例：

package com.cisco.tomcat.simpleServletServer;
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.*;

public class PrimitiveServlet implements Servlet{

	@Override
	public void init(ServletConfig config) throws ServletException {
		System.out.println("init");
		
	}

	@Override
	public ServletConfig getServletConfig() {		
		return null;
	}

	@Override
	public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
		System.out.println("from service");
		PrintWriter out = res.getWriter();
		out.println("Hello. Rose is red");
		out.println("Violets are blue");		
	}

	@Override
	public String getServletInfo() {
		return null;
	}

	@Override
	public void destroy() {
		System.out.println("destroy");		
	}

}

 

 

2 功能简单的一个Servlet Container应用

（1）功能健全的servlet container应具备四个功能：

I. 当第一次调用servlet时，应加载这个servlet class并调用init()方法

II. 为每次的request, 创建ServletRequest和ServletResponse的实例

III. 调用servlet的service()方法，并传递ServletRequest对象和ServletResponse对象

IIII. 当sevlet类shutdown, 调用servlet的destory()方法，卸载该servlet类

（2）功能简化的这个ServletContainer主要做几个功能：

I 等待HTTP requests

II 创建ServletRequest和ServletResponse对象

III 如果请求静态资源，调用StaticResourceProcessor实例的process()方法，并传递ServletRequest和ServletResponse对象

|||| 如果请求一个servlet，加载serlvet 类，调用service()方法，并传递ServletRequest和ServletResponse对象（注：这种简化版每次都会加载serlvet类）

（3）这个ServletContainer

    主要包含6个类：    HTTPServer/Request/Response/StaticResourceProcessor/ServletProcessor/Constants

     UML图如下：

 

    URL: http://127.0.0.1:8080/servlet/servletClass

（4）具体实现：

HttpServer代码（较上节server增加了静态动态资源判断，转向到staticResourceProcessor或者servletProcessor处理）：

package com.cisco.tomcat.simpleServletServer;

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 HttpServer {
	private static final String SHUTDOWN_COMMOND="/SHUTDOWN";
	private static final int PORT = 8080;
	private static final String HOST = "127.0.0.1";
	
	private boolean shutdown = false;
	
	public static void main(String[] args) {
		System.out.println("Start the Servlet Container......");
		HttpServer server = new HttpServer();
		server.await();
	}
	
	private void await() {
		ServerSocket serverSocket = null;
		try {
			serverSocket = new ServerSocket(PORT, 1, InetAddress.getByName(HOST));			
		} catch (IOException e) {
			e.printStackTrace();
			System.exit(1);
		}
		
		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
				Request request = new Request(input);
				request.parse();
				
				// 创建Response对象
				Response response = new Response(output);
				response.setRequest(request);
				
				// 判断是静态资源or Servlet，这里使用请求路径
				if(request.getUri().startsWith("/servlet/")) {
					ServletProcessor processor = new ServletProcessor();
					processor.process(request, response);					
				}else {
					StaticResourceProcessor processor = new StaticResourceProcessor();
					processor.process(request, response);
				}
				
				// 关闭socket
				socket.close();
				
				// 检查是否是关闭命令
				shutdown = SHUTDOWN_COMMOND.equals(request.getUri());
			} catch (IOException e) {
				e.printStackTrace();
				System.exit(1);
			}
			
		}

		
	}
}

 

 

Constants代码：

package com.cisco.tomcat;

import java.io.File;

public class Constants {
	public static final String WEB_ROOT = System.getProperty("user.dir")+ File.separator + "webroot";
	public static final String WEB_SERVLET_ROOT = System.getProperty("user.dir")+ File.separator + "target"+ File.separator +"classes"+ File.separator ;
}

 

 

 

Request代码：

package com.cisco.tomcat.simpleServletServer;

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.AsyncContext;
import javax.servlet.DispatcherType;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class Request implements ServletRequest {
	private InputStream input;
	private String uri;
	
	public Request(InputStream input) {
		this.input = input;
	}
	
	public String getUri() {
		return uri;
	}
	
	public void parse() {
		StringBuffer request = new StringBuffer();
		int i;
		byte[] bytes = new byte[2048];
		try {
			i = input.read(bytes, 0, 2048);
		}catch (IOException e) {
			e.printStackTrace();
			i = -1;
		}
		for(int j=0; j<i; j++) {
			request.append((char)bytes[j]);
		}
		System.out.println(request.toString());
		uri = parseUri(request.toString());		
	}
	
	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;
	}
	
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return super.toString();
	}

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

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

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

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

	}

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

	@Override
	public long getContentLengthLong() {
		// 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 getParameter(String name) {
		// TODO Auto-generated method stub
		return null;
	}

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

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

	@Override
	public Map<String, String[]> getParameterMap() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getProtocol() {
		// 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 BufferedReader getReader() throws IOException {
		// 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 void setAttribute(String name, Object o) {
		// TODO Auto-generated method stub

	}

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

	}

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

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

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

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

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

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

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

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

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

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

	@Override
	public AsyncContext startAsync() throws IllegalStateException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse)
			throws IllegalStateException {
		// TODO Auto-generated method stub
		return null;
	}

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

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

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

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

}

 

 

Response代码（静态资源的process方法放在了这里，同时提供一个PrintWriter，供Servlet内使用response对象来打印到socket管道中，response.getWriter().println()）：

package com.cisco.tomcat.simpleServletServer;

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

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

import com.cisco.tomcat.Constants;

public class Response implements ServletResponse {

	private static final int BUFFER_SIZE = 1024;
	private OutputStream output;
	private Request request;
	private PrintWriter writer;
	
	public void sendStaticResource() throws IOException{
		byte[] bytes = new byte[BUFFER_SIZE];
		FileInputStream fis = null;
		try {
			File file = new File(Constants.WEB_ROOT, request.getUri());
			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);
			}
		}catch (FileNotFoundException e) {
			String errorMessage = "HTTP/1.1 404 File Not Found\n"
					+ "Content-Type:text/html\n"
					+ "Content-Length:23\n"
					+ "\n"
					+ "<h1>File Not Found</h1>";
			output.write(errorMessage.getBytes());
		}finally {
			if(fis != null) {
				fis.close();
			}
		}
	}
	
	public void setRequest(Request request) {
		this.request = request;
	}
	
	public Response(OutputStream output) {
		this.output = output;
	}
	
	@Override
	public PrintWriter getWriter() throws IOException {
		writer = new PrintWriter(output, true);
		return writer;
	}
	
	@Override
	public String getCharacterEncoding() {
		// TODO Auto-generated method stub
		return null;
	}

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

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

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

	}

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

	}

	@Override
	public void setContentLengthLong(long length) {
		// TODO Auto-generated method stub

	}

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

	}

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

	}

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

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

	}

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

	}

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

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

	}

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

	}

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

}

 

 

ServletProcessor代码：

package com.cisco.tomcat.simpleServletServer;

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

import javax.servlet.Servlet;

import com.cisco.tomcat.Constants;

public class ServletProcessor {
	public void process(Request request, Response response) {
		String uri = request.getUri();
		String servletName = "com.cisco.tomcat.simpleServletServer." + uri.substring(uri.lastIndexOf("/")+1);
		
		// 实现URL class loader
		URLClassLoader loader = null;
		try {
			URL[] urls = new URL[1];
			URLStreamHandler streamHandler = null;
			File classPath = new File(Constants.WEB_SERVLET_ROOT);
			
			// 从org.apache.catalina.loader.StandardClassLoader/startup.ClassLoaderFactory中获取该code
			String repository = (new URL("file", null, classPath.getCanonicalPath()+File.separator)).toString();
			urls[0] = new URL(null, repository, streamHandler);
			loader = new URLClassLoader(urls);			
		}catch (IOException e) {
			System.out.println(e.toString());
		}
		
		// 加载类
		Class<?> myClass = null;
		try {
			myClass = loader.loadClass(servletName);
		}catch (Exception e) {
			System.out.println(e.toString());
		}
		
		// 反射机制生成servlet实例，并调用service()方法
		Servlet servlet = null;
		try {
			servlet = (Servlet)myClass.newInstance();
			servlet.service(request, response);
		}catch (Exception e) {
			System.out.println(e.toString());
		}
	}
}

 

 

StaticResourceProcessor代码：

package com.cisco.tomcat.simpleServletServer;

import java.io.IOException;

public class StaticResourceProcessor {
	public void process(Request request, Response response) {
		try {
			response.sendStaticResource();
		}catch (IOException e) {
			e.printStackTrace();
		}
	}
}

 

 

Servlet Container需要调用的exampleServlet.class，如果文件为

C:/example/target/classes/com/cisco/tomcat/ExampleServlet.class. 那么URLClassloader的 URL地址要配置成c:/example/target/classes/。而文件的名称也要携带包名 也就是“com.cisco.tomcat.”+"ExampleServlet", 否则URLClassLoader会报找不到class的错误信息【NoClassDefFoundError: wrong name】

 

 

3. 优化的Servlet Container

    上述servletProcessor中，使用servlet.service(request, response)时， servlet对象此时能够调用request和response的所有public方法，如getUri(),parse(), sendStaticResource()等，但实际上这可能是不安全的。所以tomcat引用了Façade Pattern(门面模式)，来解决这个问题。

    门面模式的主要作用：将子系统的各个调用封装在一个子系统对外统一接口，屏蔽内部接口实现细节

 

这里主要增加两个类：RequestFacade和ResponseFacade:

RequestFacade代码(构造函数复制私有的request对象，隐藏request的对公函数)：

public class RequestFacade implements ServletRequest{

	private ServletRequest request = null;
	
	public RequestFacade(ServletRequest request) {
		this.request = request;
	}
	@Override
	public Object getAttribute(String name) {
		return request.getAttribute(name);
	}

	@Override
	public Enumeration<String> getAttributeNames() {
		return request.getAttributeNames();
	}

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

ResponseFacade代码：

public class ResponseFacade implements ServletResponse{

	private ServletResponse response;
	
	public ResponseFacade(ServletResponse response) {
		this.response = response; 
	}
	
	@Override
	public String getCharacterEncoding() {
		return response.getCharacterEncoding();
	}

	@Override
	public String getContentType() {
		return response.getContentType();
	}

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

	@Override
	public PrintWriter getWriter() throws IOException {
		return response.getWriter();
	}
}