ServletContext对象的使用！！！

1、是什么
         tomcat启动时会为web应用创建一个servletContext对象，是Servlet的一个全局配置对象&域对象

2、配置对象怎么用：web.xml

        
     username
     root

ServletContext servletContext = getServletContext();
String username = servletContext.getInitParameter("username");

3、域对象怎么用

servletContext.setAttribute("msg", "sb");
Object msg = servletContext.getAttribute("msg");

4.主要方法：

getInitParameter() //获取指定参数名称的全局参数值
getRealPath(String path) //获得当前项目的服务器磁盘路径
getContextPath() //获取项目的根路径
getAttribute(String parameterName) //获取ServletContext域中指定名称的参数值；
setAttribute(String paramterName,Object parameterValue) //存储参数到ServletContext域中；
removeAttribute(String parameterNam) //将ServletContext域中指定名称的参数移除；

代码演示：

ServletContextDome：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package com.by.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * 
Project: JavaWeb-Servlet - ServeltContextDome
 * 
Powered by scl On 2023-12-26 17:10:19
 * 
描述：

 *
 * @author 孙臣龙 [[email protected]]
 * @version 1.0
 * @since 17
 */
public class ServletContextDome extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        ServletContext servletContext = getServletContext();
        //匹配全局属性值，也就是在web.xml文件中配置的数据
        String username = servletContext.getInitParameter("username");
        String password = servletContext.getInitParameter("password");
        System.out.println(username+password);
        //通过setAttribute()方法添加新的属性
        String str="hello";
        servletContext.setAttribute("aaa", str);
        //获取新的属性
        System.out.println(servletContext.getAttribute("aaa"));
    }
}

 ServletContextDome2：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package com.by.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * 
Project: JavaWeb-Servlet - ServeltContextDome
 * 
Powered by scl On 2023-12-26 17:10:19
 * 
描述：

 *
 * @author 孙臣龙 [[email protected]]
 * @version 1.0
 * @since 17
 */
public class ServletContextDome2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        ServletContext servletContext = getServletContext();
        //匹配全局属性值，也就是在web.xml文件中配置的数据
        String username = servletContext.getInitParameter("username");
        String password = servletContext.getInitParameter("password");
        System.out.println("第二次匹配："+username+password);
        //获取第一个Dome文件中通过setAttribute()方法添加新的属性
        System.out.println(servletContext.getAttribute("aaa"));
    }
}

web.xml:

        username
        刘亦菲
    
    
        password
        521
    
    
        ServletContextDome
        com.by.servlet.ServletContextDome
    
    
        ServletContextDome
        /servletContextDome
    
    
        ServletContextDome2
        com.by.servlet.ServletContextDome2
    
    
        ServletContextDome2
        /servletContextDome2