JavaWeb基础 session isNew 判断session是新生成的 还是旧有的

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javaEE：7           
       javaSE：1.8
          JSTL：1.2.2  
      server：tomcat 8.5
    browser：Chrome/Firefox
             os：windows7 x64
            ide：MyEclipse 2017

项目结构

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>Day11</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>

  <servlet>
  	<servlet-name>NewSessionServlet</servlet-name>
  	<servlet-class>com.jizuiku.servlet.NewSessionServlet</servlet-class>
  </servlet>

  <servlet-mapping>
  	<servlet-name>NewSessionServlet</servlet-name>
  	<url-pattern>/NewSessionServlet</url-pattern>
  </servlet-mapping>

  <servlet>
  	<servlet-name>OldSessionServlet</servlet-name>
  	<servlet-class>com.jizuiku.servlet.OldSessionServlet</servlet-class>
  </servlet>

  <servlet-mapping>
  	<servlet-name>OldSessionServlet</servlet-name>
  	<url-pattern>/OldSessionServlet</url-pattern>
  </servlet-mapping>

</web-app>

NewSessionServlet.java

package com.jizuiku.servlet;

import java.io.IOException;

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

/**
 *
 *
 * @author 博客园-给最苦
 * @version V2017.11.21
 */
public class NewSessionServlet extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		// 服务器不会马上创建session.而是 在第一次获取session时，才会创建session。理论通的重要性！
		// req.getSession();获取session
		if (req.getSession().isNew()) {
			response.getWriter().print("新生成的");
		} else {
			response.getWriter().print("旧有的");
		}

	}

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub

	}

}

OldSessionServlet.java

package com.jizuiku.servlet;

import java.io.IOException;

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

/**
 *
 *
 * @author 博客园-给最苦
 * @version V2017.11.21
 */
public class OldSessionServlet extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		// 服务器不会马上创建session.而是 在第一次获取session时，才会创建session。理论通的重要性！
		// req.getSession();获取session
		if (req.getSession().isNew()) {
			response.getWriter().print("新生成的");
		} else {
			response.getWriter().print("旧有的");
		}

	}

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub

	}

}

浏览器进行访问

　　这里要注意的是访问的先后顺序，页面的效果与访问的先后顺序是有关的

注：

　　给最苦 在做这个测试的时候，web.xml没写好，各种出错。