一个事例搞懂Servlet&JSP

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
	version="2.4">
	
	<servlet>
		<servlet-name>AllInOneServlet</servlet-name>
		<servlet-class>com.cdai.web.j2ee.AllInOneServlet</servlet-class>
	</servlet>

	<servlet-mapping>
		<servlet-name>AllInOneServlet</servlet-name>
		<url-pattern>/j2ee</url-pattern>
	</servlet-mapping>
	
	<!-- Servlet mappings END -->	

</web-app>

package com.cdai.web.j2ee;

import java.io.DataOutputStream;
import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
public class AllInOneServlet extends HttpServlet {

	public AllInOneServlet() {
		System.out.println("Servlet constructed");
	}

	@Override
	public void init() {
		System.out.println("Servlet init");
	}
	
	@Override
	public void destroy() {
		System.out.println("Servlet destory");
	}
	
	@Override
	public void service(HttpServletRequest request, HttpServletResponse response)
	        throws ServletException, IOException {
		
		System.out.println("Servlet served");

		// 1.Get parameter from HTTP header
		String goWhere = request.getParameter("goto");
		
		if (goWhere == null || "1".equals(goWhere)) {
			
			// 2.Set response header
			response.setContentType("text/html");
			
			// 3.Get useful info from TCP & HTTP header
			System.out.println(
					"Request from: " + request.getRemoteAddr() + ":" + 
					request.getRemotePort() + " by method " + 
					request.getMethod());
			
			// 4.Print html(out is built-in object in JSP)
			DataOutputStream out = new DataOutputStream(response.getOutputStream());
			out.writeUTF("Hello Servlet");
			out.writeUTF("<br>");
			out.close();
		}
		else if ("2".equals(goWhere)) {
			RequestDispatcher dispather = request.getRequestDispatcher("/main.jsp?param1=java");
			request.setAttribute("param2", "servlet");
			dispather.forward(request, response);
		}
		else if ("3".equals(goWhere)) {
			response.sendRedirect("http://www.google.com?newwindow=1&q=java&oq=java");
		}
		
	}
	
}

<!-- 1.Compile instruction -->
<%@page 
	import="java.util.concurrent.atomic.*, com.cdai.web.j2ee.TestBean" 
	contentType="text/html;charset=utf-8" 
%>

<!-- 2.Declaration: member variable and method -->
<%! 

	private AtomicInteger count = new AtomicInteger(1);
	private ThreadLocal<Integer> curCountStorage = new ThreadLocal<Integer>();
	
	private int getCount() {
		int curCount = count.getAndIncrement();
		curCountStorage.set(curCount);
		return curCount;
	}
%>

<!-- 3.JSP code & 4.Built-in object -->
<%
	Object curCount = session.getAttribute("count");
	if (curCount == null) {
		curCount = getCount();
		session.setAttribute("count", curCount);
	}
	
	out.println(request.getParameter("param1") + " - " + request.getAttribute("param2"));
%>

<br> This is main.jsp. You're the <%=curCount%> visitor.

<!-- 5.Runtime action -->
<jsp:useBean id="testBean" class="com.cdai.web.j2ee.TestBean" scope="page"/>
<br>Message in TestBean is: <jsp:getProperty property="message" name="testBean"/>

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.concurrent.atomic.*;
import com.cdai.web.j2ee.TestBean;

public final class main_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {

 

	private AtomicInteger count = new AtomicInteger(1);
	private ThreadLocal<Integer> curCountStorage = new ThreadLocal<Integer>();
	
	private int getCount() {
		int curCount = count.getAndIncrement();
		curCountStorage.set(curCount);
		return curCount;
	}

  private static java.util.List _jspx_dependants;

  public Object getDependants() {
    return _jspx_dependants;
  }

  public void _jspService(HttpServletRequest request, HttpServletResponse response)
        throws java.io.IOException, ServletException {

    JspFactory _jspxFactory = null;
    PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;
    PageContext _jspx_page_context = null;


    try {
      _jspxFactory = JspFactory.getDefaultFactory();
      response.setContentType("text/html;charset=utf-8");
      pageContext = _jspxFactory.getPageContext(this, request, response,
      			null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("<!-- 1.Compile instruction -->\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("<!-- 2.Declaration: member variable and method -->\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("<!-- 3.JSP code & 4.Built-in object -->\r\n");

	Object curCount = session.getAttribute("count");
	if (curCount == null) {
		curCount = getCount();
		session.setAttribute("count", curCount);
	}
	
	out.println(request.getParameter("param1") + " - " + request.getAttribute("param2"));

      out.write("\r\n");
      out.write("\r\n");
      out.write("<br> This is main.jsp. You're the ");
      out.print(curCount);
      out.write(" visitor.\r\n");
      out.write("\r\n");
      out.write("<!-- 5.Runtime action -->\r\n");
      com.cdai.web.j2ee.TestBean testBean = null;
      synchronized (_jspx_page_context) {
        testBean = (com.cdai.web.j2ee.TestBean) _jspx_page_context.getAttribute("testBean", PageContext.PAGE_SCOPE);
        if (testBean == null){
          testBean = new com.cdai.web.j2ee.TestBean();
          _jspx_page_context.setAttribute("testBean", testBean, PageContext.PAGE_SCOPE);
        }
      }
      out.write("\r\n");
      out.write("<br>Message in TestBean is: ");
      out.write(org.apache.jasper.runtime.JspRuntimeLibrary.toString((((com.cdai.web.j2ee.TestBean)_jspx_page_context.findAttribute("testBean")).getMessage())));
      out.write('\r');
      out.write('\n');
    } catch (Throwable t) {
      if (!(t instanceof SkipPageException)){
        out = _jspx_out;
        if (out != null && out.getBufferSize() != 0)
          out.clearBuffer();
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
      }
    } finally {
      if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}