tomcat學習筆記(二) 模擬一個簡單的servlet容器

        在上一章中模擬了一個簡單的web server，但是這個web server只能訪問靜態資源，這章將模擬一個簡單的servlet容器，可以訪問servlet。

        直接看代碼。

        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;
			}
		}
	}
}

        這個HttpServer和上一次只有一點區別，就是加了一個判斷，如果URL訪問的是servlet，就調用ServletProcessor類的process方法，如果是靜態資源，就調用StaticResourceProcessor類的方法處理，後面就會看到StaticResourceProcessor類的處理過程和上一章講的處理靜態資源的過程一樣。

        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{

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

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

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

	@Override
	public void init(ServletConfig arg0) throws ServletException {
		System.out.println("init");
	}

	@Override
	public 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");
	}

}

         這個Servlet很簡單，向頁面輸出兩句話。

         由於Servlet的service方法的參數是javax.servlet.ServletRequest和javax.servlet.ServletResponse類型的，因此前一章中用到的request和response對象要實現此接口，才能將兩個參數傳到servlet的service方法中。下面看一下request和response的代碼：

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

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

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

}

          原來的方法還保留。新的方法默認就行，現在用不到，這裏實現 javax.servlet.Request接口只是爲了能夠傳參，便於模擬。

          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
        
    }

}

         這裏要注意一點，就是Response中實現了getWriter()方法，因爲servlet中是使用response.getWrite()得到一個PrintWriter類來進行輸出的，所以這裏需要實現。可以看到這裏是用new PriintWrite(out,true);來創建PrintWriter對象的，這個out其實就是socket.getOutputResponse得到的outputStream然後再傳過來的，因此servlet中最後輸出其實本質上還是socket的輸出流輸出的，這個和上一章講的輸出是一樣的，這樣就理解了爲什麼servlet中寫個輸出就能輸出到頁面上了。

         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());
		}
	}
}

          這個類比較重要，是處理動態資源請求的核心類，但是其實也很簡單，前面做了一大堆工作，其實就是創建了個ClassLoader，把請求的servlet加載到內存，用myClass.newInstance()方法創建一個servlet的對象，然後servlet.service來調用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();
		}
	}
}

          這個很簡單，就是調用了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";
}

        將PrimitiveServlet編譯後的class文件放到webRoot目錄下，運行HttpServlet類，然後在瀏覽器上輸入http://localhost:8080/servlet/PrimitiveServlet，就可以看到效果了。

        本章中的servlet container在每次請求的時候都會加載servlet並且實例化，這個在後面會做出優化。

        歡迎大家和我一起學習，討論。