Javaweb | ServletContext对象

社区
ServletContext对象

概述

  • 全局对象,拥有作用域,对应Tomcat的Web应用
  • Web服务器启动时,会为每一个Web应用程序创建一块共享的存储区域(ServletContext)
  • ServletContext在Web服务器启动时创建,服务器关闭时销毁

获取ServletContext对象

  • GenericServlet提供 getServletContext(); 方法 this.getServletContext();
  • HttpServletRequest提供 getServletContext(); 方法
  • HttpSession提供 getServletContext(); 方法
//获取ServletContext对象
ServletContext servletContext = this.getServletContext();

//通过request对象,获取ServletContext对象
ServletContext servletContext1 = request.getServletContext();

//通过request获取session对象,获取ServletContext对象
HttpSession session = request.getSession();
ServletContext servletContext2 = session.getServletContext();

ServletContext 作用

  • 获取项目真实路径(获取当前项目在服务器发布的真实路径)
String realpath = servletContext.getRealPath("/");
        //获取ServletContext对象
        ServletContext servletContext = this.getServletContext();
        //获取项目真实路径
        System.out.println(servletContext.getRealPath("/"));

		/*
		输出结果
		D:\Eclipse\apache-tomcat-8.5.82-windows-x64\apache-tomcat-8.5.82\webapps\Servlet_Projects_war\
		*/
  • 获取项目上下文路径(获取当前项目上下文路径:应用程序名称)
System.out.println(servletContext.getContextPath());
System.out.println(request.getContextPath());
//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//获取项目上下文路径
System.out.println(servletContext.getContextPath());
System.out.println(request.getContextPath());
/*
输出结果:
/Servlet_Projects_war
/Servlet_Projects_war
*/
  • 全局容器

    ServletContext拥有作用域,可以存储数据到全局容器中

    • 存储数据: servletContext.setAttribute("name","value");
    • 获取数据: servletContext.getAttribute("name");
    • 移除数据: servletContext.removeAttribute("name");
  • ServletContextController类

@WebServlet(name = "ServletContextController", value = "/ctxController")
public class ServletContextController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = this.getServletContext();

        //获取项目真实路径
        System.out.println(servletContext.getRealPath("/"));

        //存储数据
        servletContext.setAttribute("context","info");
    }
}
  • ShowContextController类
@WebServlet(name = "ShowContextController", value = "/ShowController")
public class ShowContextController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = this.getServletContext();
        
        //获取数据
        String context = (String) servletContext.getAttribute("context");
        System.out.println(context);
        
         /*
        输出结果:
        D:\Eclipse\apache-tomcat-8.5.82-windows-x64\apache-tomcat-8.5.82\webapps\Servlet_Projects_war\
        info
        */
    }
}

ServletContext 特点

  • 唯一性:一个应用对应一个ServletContext
  • 生命周期:只要容器不关闭或者应用不卸载,ServletContext就一直存在

ServletContext 应用场景

  • CounterController类
@WebServlet(name = "CounterController", value = "/counterController")
public class CounterController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = request.getServletContext();

        //获取计数器
        Integer counter = (Integer) servletContext.getAttribute("counter");

        //计数器初始化
        if (counter == null) {
            counter = 1;
            //counter存入计数器
            servletContext.setAttribute("counter", counter);
        } else {
            counter++;
            servletContext.setAttribute("counter", counter);
        }
        
        System.out.println("counter:" + counter);

    }
}
  • ShowCounterController类
@WebServlet(name = "ShowCounterController", value = "/ShowCounterController")
public class ShowCounterController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = request.getServletContext();

        //获取计数器
        Integer counter = (Integer) servletContext.getAttribute("counter");
        
        //计数器初始化
        if (counter == null) {
            counter = 1;
            //counter存入计数器
            servletContext.setAttribute("counter", counter);
        } else {
            counter++;
            servletContext.setAttribute("counter", counter);
        }

        System.out.println("show:" + counter);
    }
}
  • 结果
counter:1
show:2
show:3
show:4
show:5
show:6
show:7

作用域总结

  • HttpServletRequest:一次请求,请求响应之前有效
  • HttpSession:一次会话开始,浏览器不关闭或不超时之前有效
  • ServletContext:服务器启动开始,服务器停止之前有效
0
0
0
0
相关产品
评论
未登录
看完啦,登录分享一下感受吧~
暂无评论