Filter

Filter快速入门

1. 定义类，实现Filter接口，并重写其所有方法
2. 配置Filter拦截资源的路径：在类上定义@WebFilter注解
3. 在doFilter方法中输出一句话，并放行

@WebFilter("/*")
public class FilterDemo implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("filter");
        //放行
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void destroy() {
    }
}

Filter执行流程

放行前逻辑
放行
放行后逻辑

@WebFilter("/*")
public class FilterDemo implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //1. 放行前，对request数据进行处理
        System.out.println("filter");
        //2. 放行
        filterChain.doFilter(servletRequest, servletResponse);
        //3. 放行后，对response数据进行处理
        System.out.println("filter end");
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void destroy() {
    }
}

Filter使用细节

Filter拦截路径的配置

过滤器链

Filter案例

此案例与JavaWeb_11_Cookie&Session中案例一样，只是多加了过滤器

//com.ziping.web.filter.LoginFilter.java
@WebFilter("/*")
public class LoginFilter implements Filter{
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        //0. 判断访问资源是否和登录注册相关
        String[] urls = {"/login.jsp", "/register.jsp", "/loginServlet", "/registerServlet", "/checkCodeServlet"};
        // 获取当前访问的资源路径
        String s = request.getRequestURL().toString();
        //判断
        for (String url : urls) {
            if(s.contains(url)){
                //找到了，放行
                filterChain.doFilter(servletRequest,servletResponse);
                return;
            }
        }
        //1. 判断session中是否有user键
        HttpSession session = request.getSession();
        Object user = session.getAttribute("user");
        //2. 判断user是否为空
        if(user != null){
            //放行
            filterChain.doFilter(servletRequest,servletResponse);
        }else{
            //跳转到登录页面
            //存储提示信息
            request.setAttribute("login_msg","请先登录");
            request.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
        }
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void destroy() {
    }
}

Listener

监听器分类	监听器名称	作用
ServletContext监听	ServletContextListener	对ServletContext对象的监听
	ServletContextAttributeListener	对ServletContext对象中属性的监听
Session监听	HttpSessionListener	对Session对象的监听
	HttpSessionAttributetListener	对Session对象中属性的监听
	HttpSessionBindingListener	监听对象与Session的绑定和接触
	HttpSessionActivationListener	对Session数据钝化、活化的监听
Request监听	ServletRequestListener	对Request对象的监听
	ServletRequestAttributeListener	对Request对象中属性的监听

ServletContextListener使用

1. 定义类，实现ServletContextListener接口
2. 在类上添加@WebListener注解

//com.ziping.web.listener.ContextLoaderListener.java
@WebListener
public class ContextLoaderListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //加载资源
        System.out.println("ContextLoaderListener...");
    }
    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        //释放资源
    }
}

案例资源

12_JavaWeb——Filter&Listener