Servlet学习之ServletContext对象

Servlet学习之ServletContext对象

我们想要实现Servlet中实现数据共享，那么我们就需要学习新的东西了，这个就是ServletContext上下文对象，请看下图是就是Servlet中如何使用ServletContext来实现数据共享的。

其实就是HelloServlet把数据放到Servletcontext中，GetServlet再去把里边的数据取出来。这样就是实现了HelloServlet和GetServlet的数据共享

下边是具体的实现

 <servlet>
    <servlet-name>Hello</servlet-name>
    <servlet-class>com.ke.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Hello</servlet-name>
    <url-pattern>/set</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>Get</servlet-name>
    <servlet-class>com.ke.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Get</servlet-name>
    <url-pattern>/get</url-pattern>
  </servlet-mapping>

package com.ke.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 {
        ServletContext context = this.getServletContext();

        String name = "王五";
        context.setAttribute("name",name); //将一个数据保存在Servlet中，名字为name ，值为 name
    }
}

package com.ke.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 names = (String)context.getAttribute("name");

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

        resp.getWriter().print("名字："+names);
    }

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

如果先访问get那么名字是null，因为HelloServlet还没有把数据放进去。要先访问/set在访问/get