tomcat学习笔记(二) 模拟一个简单的servlet容器

来源：互联网发布：mysql 最近一条记录编辑：程序博客网时间：2024/04/19 07:17

在上一章中模拟了一个简单的web server，但是这个web server只能访问静态资源，这章将模拟一个简单的servlet容器，可以访问servlet。

直接看代码。

HttpServer:

package com.serveletcontainer;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_COMMAND = "/SHUTDOWN";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(Exception e){e.printStackTrace();System.exit(1);}while(!shutdown){Socket socket = null;InputStream in = null;OutputStream out = null;try {socket = serverSocket.accept();in = socket.getInputStream();out = socket.getOutputStream();Request request = new Request(in);request.parse();Response response = new Response(out);response.setRequest(request);if(request.getUri().startsWith("/servlet/")){ServletProcessor processor = new ServletProcessor();processor.process(request, response);}else{StaticResourceProcessor processor = new StaticResourceProcessor();processor.process(request, response);}//response.sendStaticResource();socket.close();shutdown = request.getUri().equals("SHUTDOWN_COMMAND");} catch (IOException e) {e.printStackTrace();continue;}}}}

这个HttpServer和上一次只有一点区别，就是加了一个判断，如果URL访问的是servlet，就调用ServletProcessor类的process方法，如果是静态资源，就调用StaticResourceProcessor类的方法处理，后面就会看到StaticResourceProcessor类的处理过程和上一章讲的处理静态资源的过程一样。

PrimitiveServlet：

import java.io.IOException;import java.io.PrintWriter;import javax.servlet.Servlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class PrimitiveServlet implements Servlet{@Overridepublic void destroy() {System.out.println("destory");}@Overridepublic ServletConfig getServletConfig() {return null;}@Overridepublic String getServletInfo() {return null;}@Overridepublic void init(ServletConfig arg0) throws ServletException {System.out.println("init");}@Overridepublic void service(ServletRequest request, ServletResponse response)throws ServletException, IOException {System.out.println("from Service");PrintWriter out = response.getWriter();out.println("Hello.Roses are red.");out.println("Violets are blue");}}

这个Servlet很简单，向页面输出两句话。

由于Servlet的service方法的参数是javax.servlet.ServletRequest和javax.servlet.ServletResponse类型的，因此前一章中用到的request和response对象要实现此接口，才能将两个参数传到servlet的service方法中。下面看一下request和response的代码：

Request.java:

package com.serveletcontainer;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 InputStream input;private String uri;public Request(InputStream input){this.input = input;}public void parse(){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());}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;}@Overridepublic Object getAttribute(String arg0) {// TODO Auto-generated method stubreturn null;}@Overridepublic Enumeration getAttributeNames() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getCharacterEncoding() {// TODO Auto-generated method stubreturn null;}@Overridepublic int getContentLength() {// TODO Auto-generated method stubreturn 0;}@Overridepublic String getContentType() {// TODO Auto-generated method stubreturn null;}@Overridepublic ServletInputStream getInputStream() throws IOException {// TODO Auto-generated method stubreturn null;}@Overridepublic String getLocalAddr() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getLocalName() {// TODO Auto-generated method stubreturn null;}@Overridepublic int getLocalPort() {// TODO Auto-generated method stubreturn 0;}@Overridepublic Locale getLocale() {// TODO Auto-generated method stubreturn null;}@Overridepublic Enumeration getLocales() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getParameter(String arg0) {// TODO Auto-generated method stubreturn null;}@Overridepublic Map getParameterMap() {// TODO Auto-generated method stubreturn null;}@Overridepublic Enumeration getParameterNames() {// TODO Auto-generated method stubreturn null;}@Overridepublic String[] getParameterValues(String arg0) {// TODO Auto-generated method stubreturn null;}@Overridepublic String getProtocol() {// TODO Auto-generated method stubreturn null;}@Overridepublic BufferedReader getReader() throws IOException {// TODO Auto-generated method stubreturn null;}@Overridepublic String getRealPath(String arg0) {// TODO Auto-generated method stubreturn null;}@Overridepublic String getRemoteAddr() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getRemoteHost() {// TODO Auto-generated method stubreturn null;}@Overridepublic int getRemotePort() {// TODO Auto-generated method stubreturn 0;}@Overridepublic RequestDispatcher getRequestDispatcher(String arg0) {// TODO Auto-generated method stubreturn null;}@Overridepublic String getScheme() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getServerName() {// TODO Auto-generated method stubreturn null;}@Overridepublic int getServerPort() {// TODO Auto-generated method stubreturn 0;}@Overridepublic boolean isSecure() {// TODO Auto-generated method stubreturn false;}@Overridepublic void removeAttribute(String arg0) {// TODO Auto-generated method stub}@Overridepublic void setAttribute(String arg0, Object arg1) {// TODO Auto-generated method stub}@Overridepublic void setCharacterEncoding(String arg0)throws UnsupportedEncodingException {// TODO Auto-generated method stub}}

原来的方法还保留。新的方法默认就行，现在用不到，这里实现 javax.servlet.Request接口只是为了能够传参，便于模拟。

Response.java:

          package com.serveletcontainer;

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;
   Request request;
   OutputStream out;
   PrintWriter writer;
   public Response(OutputStream out){
       this.out = out;
   }
   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(Constants.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 errorMessage = "HTTP/1.1 404 File Not Found\n" +
                   "Content-Type:text/html\n" +
                   "Content-Length:23\n" +
                   "\n" +
                   "<h1>File not Found</h1>";
               out.write(errorMessage.getBytes());
           }
       }catch(Exception e){
           System.out.println(e.toString());
       }finally{
           if(fis != null)
               fis.close();
       }
   }

   @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(int arg0) {
       // TODO Auto-generated method stub

   }

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

   }

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

   }

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

   }

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

   }

}

         这里要注意一点，就是Response中实现了getWriter()方法，因为servlet中是使用response.getWrite()得到一个PrintWriter类来进行输出的，所以这里需要实现。可以看到这里是用new PriintWrite(out,true);来创建PrintWriter对象的，这个out其实就是socket.getOutputResponse得到的outputStream然后再传过来的，因此servlet中最后输出其实本质上还是socket的输出流输出的，这个和上一章讲的输出是一样的，这样就理解了为什么servlet中写个输出就能输出到页面上了。

ServletProcessor:

package com.serveletcontainer;import java.io.File;import java.net.URL;import java.net.URLClassLoader;import java.net.URLStreamHandler;import javax.servlet.Servlet;public class ServletProcessor {public void process(Request request,Response response){String uri = request.getUri();String servletName = uri.substring(uri.lastIndexOf("/")+1);URLClassLoader loader = null;try{URL []urls = new URL[1];URLStreamHandler streamHandler = null;File classPath = new File(Constants.WEB_ROOT);String repository = (new URL("file",null,classPath.getCanonicalPath()+File.separator)).toString();urls[0] = new URL(null,repository,streamHandler);System.out.println("urls: " + urls[0].toString());loader = new URLClassLoader(urls);}catch(Exception e){e.printStackTrace();}Class myClass = null;try{myClass = loader.loadClass(servletName);}catch(ClassNotFoundException e){e.printStackTrace();}Servlet servlet = null;try{servlet = (Servlet)myClass.newInstance();servlet.service(request, response);}catch(Exception e){System.out.println(e.toString());}catch(Throwable e){System.out.println(e.toString());}}}

这个类比较重要，是处理动态资源请求的核心类，但是其实也很简单，前面做了一大堆工作，其实就是创建了个ClassLoader，把请求的servlet加载到内存，用myClass.newInstance()方法创建一个servlet的对象，然后servlet.service来调用service方法。

StaticResourceProcessor:

package com.serveletcontainer;import java.io.IOException;public class StaticResourceProcessor {public void process(Request request,Response response){try {((Response)response).sendStaticResource();} catch (IOException e) {e.printStackTrace();}}}

这个很简单，就是调用了response的sendStaticResource方法。

Constants.java:

package com.serveletcontainer;import java.io.File;public class Constants {public static final String WEB_ROOT=System.getProperty("user.dir")+File.separator+"webRoot";}

将PrimitiveServlet编译后的class文件放到webRoot目录下，运行HttpServlet类，然后在浏览器上输入http://localhost:8080/servlet/PrimitiveServlet，就可以看到效果了。

本章中的servlet container在每次请求的时候都会加载servlet并且实例化，这个在后面会做出优化。

欢迎大家和我一起学习，讨论。

0 0