ServletContext对象

简述： ServletContext对象的实操。

本文初发于 “曾晨de小站” zengchen233.cn，同步转载于此。

最近在B站【狂神说Java】JavaWeb入门到实战上学习JavaWeb，学到了ServletContext对象，就想着把学习内容写下来分享给大家。

HelloServlet.java

package cn.zengchen233.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 HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

//        this.getInitParameter();  //初始化参数
//        this.getServletConfig();  //servlet的配置
//        this.getServletContext(); //servlet的上下文
        ServletContext context = this.getServletContext();
        String username = "曾晨"; //数据
        context.setAttribute("username",username);  //将一个数据保存在了ServletContext中，名字username，值username
        System.out.println("Hello,Servlet!");
    }

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

GetServlet.java

package cn.zengchen233.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");

        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);
    }
}

web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  
  <servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>cn.zengchen233.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>get</servlet-name>
    <servlet-class>cn.zengchen233.servlet.GetServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>get</servlet-name>
    <url-pattern>/get</url-pattern>
  </servlet-mapping>
</web-app>

项目运行起来后先请求/hello,然后请求/get就会显示如下结果：

Tips:必须先请求/hello,否则会显示 名字：NULL