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
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1.1、简单的登录案例
<%--
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User: yoya
Date: 2021/7/18
Time: 10:36
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--%>
<%@ 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: yoya
Date: 2021/7/19
Time: 19:41
To 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 {
@Override
public 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);
else
httpServletResponse.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 {
@Override
public 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);
else
httpServletResponse.sendRedirect(httpServletRequest.getContextPath());
System.out.println("3333333333333333333333");
}
}
1.3、多过滤器
1.4、过滤器的优点
- 实现代码的“可插拔性”，即增加或减少某个功能模块，不会影响程序的正常执行
- 可以将多个相同处理逻辑的模块集中写在过滤器里面，可实现重复利用、也方便代码的维护
2、 Listener
用来监听Servlet容器产生的事件并进行相应的处理
这玩意很强，但是没看出来有什么用，待补