session 和ServletContext对比

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比较session和ServletContext用法

session实现访问次数的例子

Java代码

//ShowTimesServlet.java /*Servlet实现访问次数的例子!*/
import java.io.*;
import java.util.zip.*;
import javax.servlet.*;
import javax.servlet.http.*;
/*
这个类实现访问次数。显示访问次数！看是第几次访问！
*/
public class ShowTimesServlet extends HttpServlet {
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException, java.io.IOException {
response.setContentType("text/html");
HttpSession session = request.getSession();
String heading;
Integer accessCount =(Integer)session.getAttribute("accessCount");
if(accessCount == null) {
accessCount = new Integer(0);
heading = "Welcom,You are first time to visit!";
}
else {
heading = "Welcome Backer";
accessCount = new Integer(accessCount.intValue()+1);
}
session.setAttribute("accessCount",accessCount);
PrintWriter out = response.getWriter();
out.println("The title:"+heading);
out.println("Access count: "+accessCount);
}
public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException, java.io.IOException {
doGet(request,response);
}
}

//ShowTimesServlet.java /*Servlet实现访问次数的例子!*/import java.io.*;import java.util.zip.*;import javax.servlet.*;import javax.servlet.http.*;/* 这个类实现访问次数。显示访问次数！看是第几次访问！*/public class ShowTimesServlet extends HttpServlet { public void doGet(HttpServletRequest request,HttpServletResponse response)               throws ServletException, java.io.IOException {            response.setContentType("text/html");   HttpSession session = request.getSession();   String heading;   Integer accessCount =(Integer)session.getAttribute("accessCount");   if(accessCount == null) {    accessCount = new Integer(0);    heading = "Welcom,You are first time to visit!";   }   else {    heading = "Welcome Backer";    accessCount = new Integer(accessCount.intValue()+1);   }      session.setAttribute("accessCount",accessCount);   PrintWriter out = response.getWriter();   out.println("The title:"+heading);   out.println("Access count: "+accessCount); } public void doPost(HttpServletRequest request,HttpServletResponse response)               throws ServletException, java.io.IOException {  doGet(request,response); }}

下面是通过servleContext来做访问次数

Java代码

package org.linweihan.test;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServletContext extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
Integer accessCount =(Integer)servletContext.getAttribute("accessCount");
if(accessCount == null){
accessCount = 0;
}else{
accessCount = accessCount + 1;
}
servletContext.setAttribute("accessCount", accessCount);
PrintWriter out = response.getWriter();
out.println("<html><body><h2>"+accessCount+"</body></html>");
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}

package org.linweihan.test;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class TestServletContext extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {ServletContext servletContext = this.getServletContext();Integer accessCount =(Integer)servletContext.getAttribute("accessCount");if(accessCount == null){accessCount = 0;}else{accessCount = accessCount + 1;}servletContext.setAttribute("accessCount", accessCount);PrintWriter out = response.getWriter();out.println("<html><body><h2>"+accessCount+"</body></html>");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}}

区别在于session是局部的,servletContext是共享的.
当换了另一个窗口开始访问又从0开始计数,而servletContext则是接下去计数.