JAVA WEB篇4——Filter、Listener

1、Filter

Filter本意为”过滤“的含义，是JavaWeb的三大组件之一，三大组件为：Servlet、Filter、 Listener
过滤器是向 Web 应用程序的请求和响应处理添加功能的 Web 服务组件
过滤器相当于浏览器与Web资源之间的一道过滤网，在访问资源之前通过一系列的过滤器对请求进行修改、判断以及拦截等，也可以对响应进行修改、判断以及拦截等

1.1、简单的登录案例

<%--Created by IntelliJ IDEA.User: yoyaDate: 2021/7/18Time: 10:36To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html><head><title>$Title$</title></head><body><form action="${pageContext.request.contextPath}/RuoyrServlet"><input type="text" name="pwd"><input type="submit" value="提交"></form></body>
</html>

@WebServlet("/RuoyrServlet")
public class RuoyrServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {System.out.println("22222222222222222222222");String pwd = request.getParameter("pwd");request.getSession().setAttribute("pwd",pwd);if (pwd.equalsIgnoreCase("123"))response.sendRedirect(request.getContextPath()+"/success.jsp");}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request,response);}
}

<%--Created by IntelliJ IDEA.User: yoyaDate: 2021/7/19Time: 19:41To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Title</title>
</head>
<body>
<%if (session.getAttribute("pwd")==null)response.sendRedirect(request.getContextPath()+"/index.jsp");
%>
<h1>登陆成功</h1>
</body>
</html>

每次都在jsp里写判断有点麻烦

1.2、Filter使用方式

如果有多个过滤器都满足过滤的条件，则容器依据映射的先后顺序来调用各个过滤器

1.2.1、web.xml

<?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"><filter><filter-name>RuoyeFilter</filter-name><filter-class>RuoyeFilter</filter-class></filter><filter-mapping><filter-name>RuoyeFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>
</web-app>

@WebFilter(urlPatterns = { "/*" })
public class RuoyeFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("11111111111111111");//放行HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;HttpServletResponse httpServletResponse= (HttpServletResponse) servletResponse;System.out.println(httpServletRequest.getServletPath());if (httpServletRequest.getSession().getAttribute("pwd")!=null||httpServletRequest.getServletPath().equals("/RuoyrServlet")||httpServletRequest.getServletPath().equals("/index.jsp"))filterChain.doFilter(servletRequest,servletResponse);elsehttpServletResponse.sendRedirect(httpServletRequest.getContextPath());System.out.println("3333333333333333333333");}
}

注意导的包 import javax.servlet.annotation.WebFilter;

1.2.2、@WebFilter

@WebFilter(urlPatterns = { "/*" })
public class RuoyeFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("11111111111111111");//放行HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;HttpServletResponse httpServletResponse= (HttpServletResponse) servletResponse;System.out.println(httpServletRequest.getServletPath());if (httpServletRequest.getSession().getAttribute("pwd")!=null||httpServletRequest.getServletPath().equals("/RuoyrServlet")||httpServletRequest.getServletPath().equals("/index.jsp"))filterChain.doFilter(servletRequest,servletResponse);elsehttpServletResponse.sendRedirect(httpServletRequest.getContextPath());System.out.println("3333333333333333333333");}
}