ServlertContext

1、ServletContext代表着整个JavaWeb应用，每个项目只有唯一的ServletContext的实例。

2、生命周期

　　服务器启动时创建

　　服务器关闭时销毁

3、获取ServletContext对象

　　方式1：通过ServletConfig来获取ServeltContext

//获取ServletContext的引用
public class ServletDemo1 extends HttpServlet {

    private ServletConfig config;

    public void init(ServletConfig config) throws ServletException {
        this.config = config;
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        ServletContext sc = config.getServletContext();
        sc.setAttribute("p", "abc");

        //获取全局参数
        System.out.println(sc.getInitParameter("encoding"));

        System.out.println("Demo1:"+sc);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}

方式2：直接获取，推荐

public class ServletDemo2 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {　　　　　//获取ServletContext
        ServletContext sc = getServletContext();
        Object value = sc.getAttribute("p");
        //获取全局参数
        System.out.println(sc.getInitParameter("encoding"));
        System.out.println(">>>>>>>:"+value);
        System.out.println("Demo2:"+sc);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}

4、ServletContext应用

　　、实现多个Servlet之间的数据共享，ServletContext叫做一个域（范围）对象