06-ServletContext

ServletContext

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

• 共享数据

我在这个Servlet中保存的数据，可以在另外一个servlet中拿到

代码演示

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username="张三";
        context.setAttribute("username",username);
        //将一个数据保存到了ServletContext中，名字为username，值为username 即张三
    }

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

public class GetServlet extends  HelloServlet{
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");
        resp.getWriter().write(username);
    }

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

<?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">

<servlet>
    <servlet-name>HelloServlet</servlet-name>
    <servlet-class>com.tian.servlet.HelloServlet</servlet-class>
</servlet>
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>GetServlet</servlet-name>
        <servlet-class>com.tian.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>GetServlet</servlet-name>
        <url-pattern>/get</url-pattern>
    </servlet-mapping>
</web-app>

测试访问结果