Servlet 上下文数据共享

小咪咪 2022-06-08 10:55 159阅读 0赞

**Servlet 上下文：**

web容器启动之后，会为每一个Web应用创建唯一的一个符合ServletContext接口要求的对象，该对象就是servlet上下文。ServletContext，是一个全局的储存信息的空间，服务器开始就存在，服务器关闭才释放。

配置好web.xml 和 完成servlet处理后将web应用部署到Tomcat，在游览器输入 http:http://localhost:8080/test，在控制台就可以观察到结果。  
  
  
**示例如下：**

**一、 web.xml 配置**

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://java.sun.com/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    		  http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
             version="2.5">
    
    
        <servlet>
    	     
            <servlet-name>ServletContextTest</servlet-name>
    		 
            <servlet-class>com.test.servlet.ServletContextTest</servlet-class>
    		
            
            <init-param>
                <param-name>name</param-name>
                <param-value>Bob</param-value>
            </init-param>
            <init-param>
                <param-name>sex</param-name>
                <param-value>男</param-value>
            </init-param>
            
            <load-on-startup>2</load-on-startup>
        </servlet>
    	
    	
        <servlet-mapping>
    		
            <servlet-name>ServletContextTest</servlet-name>
    		
            <url-pattern>/test</url-pattern>
        </servlet-mapping>
    
    
        
        <context-param>
            
            <description>定义上下文的初始化参数</description>
            
            <param-name>a</param-name>
            
            <param-value>测试</param-value>
        </context-param>
    </web-app>

**二、 serlvet处理(ServletContextTest.java)**

package com.test.servlet;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    
    public class ServletContextTest extends HttpServlet {
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //获取 ServletContextTest 初始化参数
            String name = getServletConfig().getInitParameter("name");
            String sex = getServletConfig().getInitParameter("sex");
            System.out.println("name:" + name);
            System.out.println("sex:" + sex);
    
    
            //获取上下文的初始化参数
            String test = getServletConfig().getServletContext().getInitParameter("a");
    //      String test1 = getServletContext().getInitParameter("a");//等价于上面可以省略getServletConfig()
    
    
            System.out.println("上下文的初始化参数:" + test);
    
    //        使用Servlet上下文的作用：多个web组件共享的数据
            // 绑定数据
            request.setAttribute("b", "多个web组件共享的数据");
            //获取数据
            Object b = request.getAttribute("b");
            System.out.println(b);
            //移除绑定数据
    //      request.removeAttribute("b");
    
        }
    
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doPost(request, response);
        }
    }

**三、 结果**  
  
![Center][]

[Center]: /images/20220608/34b133f9e4e842ec87d7d8117208e00d.png