ServletContext 注册web应用的三大组件 servlet、filter、listener

1、ServletContext 注册三大组件的时间

必须是在项目启动的时候，项目运行起来后就不行了，出于安全的考虑

2、ServletContext注册三大组件的位置

2.1 实现了ServletContainerInitializer接口的onStartup方法里

public class MyServletInit implements ServletContainerInitializer {
   
    public void onStartup(Set<Class<?>> set, ServletContext servletContext) throws ServletException {

      
        //注册servlet
        ServletRegistration.Dynamic servlet =servletContext.addServlet("userServlet",new UserServlet());

        //配置servlet的映射信息
        servlet.addMapping("/user");


        //注册filter
        FilterRegistration.Dynamic filter = servletContext.addFilter("userFilter",UserFilter.class);
        //配置filter 的映射信息
        filter.addMappingForServletNames(EnumSet.of(DispatcherType.REQUEST),true,"userServlet");


        //注册listener
        servletContext.addListener(UserListener.class);

        
    }


}

//自定义一个Servlet
public class UserServlet extends HttpServlet {

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

        String method =  req.getParameter("method");

        if(method.equals("add")){

            req.getSession().setAttribute("msg","执行了add 方法");

        }

        if(method.equals("delete")){
            req.getSession().setAttribute("msg","执行了delete方法");
        }


        //转发
        req.getRequestDispatcher("/WEB-INF/jsp/test.jsp").forward(req,resp);
        //重定向
        // resp.sendRedirect();


    }

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


    }
}

/**
 *
 * 自定义一个监听器 监听项目的启动和停止的
 *
 */
public class UserListener implements ServletContextListener {
    /**
     *servletContext 启动和初始化
     * @param servletContextEvent
     */
    public void contextInitialized(ServletContextEvent servletContextEvent) {


        System.out.println("UserListener。。。。 contextInitialized");
    }

    /**
     *servletContext的销毁
     *
     * @param servletContextEvent
     */
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

        System.out.println("UserListener。。。。contextDestroyed");
    }
}

/**
 * 
 * 自定义一个filter
 * 
 * 
 */
public class UserFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    /**
     *
     * 过滤请求的
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {


        System.out.println("执行了 userfilter ....");

        //对请求进行了放行
        filterChain.doFilter(servletRequest,servletResponse);
    }

    public void destroy() {

    }
}

 

3、测试结果