ServletContext实现数据共享

ServletContext实现数据共享

1、 加入新Module

 

补全项目，并把web.xml更新

  

建目录，建类HelloServlet：

  

 

2、 getServletContext(上下文对象)的作用

package com.wang.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;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

ServletContext是一个凌驾于所有的servlet之上的东西，web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用。

ServletContext对象的主要作用：共享数据：在一个servlet中保存的数据，可以在另一个servlet中拿到。

3、 ServletContext(上下文对象)的使用

1、在一个servlet类中放入数据（在HelloServlet类里），在另一个servlet类中读取数据（在GetServlet类里），这两个类中用ServletContext context = this.getServletContext();得到的是同一个ServletContext对象，

    ServletContext对象全局唯一。

 

 

 

 

     2.1 HelloServlet代码

package com.wang.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;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = "王赞";
        context.setAttribute("username",username);//将一个数据保存在ServletContext中，名字为：username，值为：王赞
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

     2.2 GetServlet代码

package com.wang.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;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");  //咱们自己知道类型，所以强转下，告诉计算机
        //输出到网页上看看
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字"+username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

2、注册加映射

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <!--注册和映射：设置数据部分-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.wang.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <!--注册和映射：获取数据部分-->
    <servlet>
        <servlet-name>getc</servlet-name>
        <servlet-class>com.wang.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>
</web-app>

3、解决中文乱码问题

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");

4、重新指定Tomcate，把名字从s1改为s2

  

5、先放数据，再读数据的先后过程