servlet中 servlet context与 session与 request三个对象的常用方法和存放数据的作用域。

提示:context，session，request，作为Servlet之间重要的传值手段，对于他们作用域的区分，使我们学习的重难点。

目录

一、Servlet的三大数据存放对象

  ①ServletContext

  ②HttpSession

  ③HttpServletRequest

三者公共方法（API）

二、作用域 

ServletContext：（服务器启动到服务器关闭。）

HttpSession：一次会话，当session销毁时结束（默认为短暂会话，若要持久会话需要设置最大存活期session.setMaxInactiveInterval(秒数);）。 

HttpServletRequest：一次请求。 

三、 使用场景

---

前言：本篇文章我们将从三者的基本概念开始进行阐述，从三者之间的优缺点入手，进而分析他们之间作用域的异同。

一、Servlet的三大数据存放对象

  ①ServletContext

        WEB容器在启动时，它会为每个WEB应用程序都创建一个对应的ServletContext对象，它代表当前web应用。ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，可以通过config.getServletContext()方法获得ServletContext对象。 

  ②HttpSession

        创建于服务器端，保存于服务器，维护于服务器端,每创建一个新的Session,服务器端都会分配一个唯一的ID，并且把这个ID保存到客户端的Cookie中，保存形式是以JSESSIONID来保存的。

  ③HttpServletRequest

        HttpServletRequest对象代表客户端的请求，当客户端通过HTTP协议访问服务器时，HTTP请求头中的所有信息都封装在这个对象中，通过这个对象提供的方法，可以获得客户端请求的所有信息。

三者公共方法（API）

存储数据：setAttribute（name，value）；

获取数据：getAttribute（name）；

删除数据： removeAttribute（name）；

二、作用域 

ServletContext：（服务器启动到服务器关闭。）

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.thymeleaf.context.WebContext;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		ServletContext context = getServletContext();
		//request域
		String name = "猪八戒";
		context.setAttribute("name", name);
		//打印到页面
		out.print("页面1"+context.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		ServletContext context = getServletContext();
		//request域
		//打印到页面
		out.print("页面2"+context.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

 运行结果：

当前edge浏览器都可以请求到

 

 换一个火狐浏览器也可以请求到

 

HttpSession：一次会话，当session销毁时结束（默认为短暂会话，若要持久会话需要设置最大存活期session.setMaxInactiveInterval(秒数);）。 

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.thymeleaf.context.WebContext;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		HttpSession session = request.getSession();
		//request域
		String name = "沙和尚";
		session.setAttribute("name", name);
		//打印到页面
		out.print("页面1"+session.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		HttpSession session = request.getSession();
		//request域
		//打印到页面
		out.print("页面2"+session.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

 运行结果：

当前edge浏览器都可以请求到

 

 换一个火狐浏览器请求不到

 

 

HttpServletRequest：一次请求。 

Test01 

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Test01
 */
@WebServlet("/Test01")
public class Test01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		
		//request域
		String name = "孙悟空";
		request.setAttribute("name", name);
		//打印到页面
		out.print("页面1"+request.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

Test02

package com.ape.view;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Test02
 */
@WebServlet("/Test02")
public class Test02 extends HttpServlet {
	private static final long serialVersionUID = 1L;
    
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 处理乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		
		//获取资源
		PrintWriter out = response.getWriter();
		
		//request域
		//打印到页面
		out.print("页面2"+request.getAttribute("name"));
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

 运行结果：

 

当进行转发后： （地址栏不变，但request请求完成了）

 

 

三、 使用场景

Request域：跟当前操作有关，可以通过转发传值到其他页面。

Session域：是一次回话，只能用于当前浏览器，适用于跟用户信息相关的，比如保存登录信息。

application域：公共的，都可以调用在整个项目运行期间，存储全局信息，一些重要信息不建议使用。

最后大家：

新的一周元气满满(*^▽^*)！！！