【Servlet】Java Serlvet Filter 过滤器
Filter的设计思想
Filter是一种AOP(aspect-oriented programming)的设计思想 : 面向切面编程。用于的请求和响应都会走
使用filter的登录案例
我们通过一张图片理解理解filer面向切面(注意:这张图片有点表示不清楚,图中只是表明了用户请求会经过过滤器,但是响应用户也是会经过过滤器的,图中并没有表示这一点)。
下面是项目的结构:
下面是jsp文件:
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
</head>
<body>
<form action="login.do" method="POST">
<span>用户名:</span><span><input type="text" name="uname" /></span><br/>
<span>密码:</span><span><input type="password" name="upass" /></span><br/>
<input type="submit" value="提交"/>
</form>
</body>
</html>
下面是web.xml文件:
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> <display-name>Filter_Demo</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> </welcome-file-list> <!-- 设置请求的编码格式的过滤器 --> <filter> <filter-name>request</filter-name> <filter-class>cn.userLogin.filter.RequestFilter</filter-class> </filter> <filter-mapping> <filter-name>request</filter-name> <url-pattern>*.do</url-pattern> </filter-mapping> <!-- 设置响应的编码格式的过滤器 --> <filter> <filter-name>response</filter-name> <filter-class>cn.userLogin.filter.ResponseFilter</filter-class> </filter> <filter-mapping> <filter-name>response</filter-name> <url-pattern>*.do</url-pattern> </filter-mapping> <!-- 设置检查参数的格式编码器 --> <filter> <filter-name>param</filter-name> <filter-class>cn.userLogin.filter.ParamFilter</filter-class> </filter> <filter-mapping> <filter-name>param</filter-name> <url-pattern>*.do</url-pattern> </filter-mapping> </web-app>
下面是servelet文件
package cn.user.servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class UserLogin */ @WebServlet("/login.do") public class UserLogin extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //进行数据判断 String userName=request.getParameter("uname"); String userPassword=request.getParameter("upass"); //从数据库中查询相应的信息... //将信息返回 response.getWriter().append("姓名:"+userName+",密码:"+userPassword); } }
下面是filter文件:
package cn.userLogin.filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.annotation.WebFilter; /** * 这个过滤器设置请求的编码格式 */ public class RequestFilter implements Filter { public void destroy() { // TODO Auto-generated method stub } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //设置请求的编码格式 request.setCharacterEncoding("utf-8"); //放行 chain.doFilter(request, response); } public void init(FilterConfig fConfig) throws ServletException { } }
package cn.userLogin.filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; /** * 这个过滤器设置响应的编码格式 */ public class ResponseFilter implements Filter { /** * 过滤器销毁的时候调用 */ public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //设置响应的编码格式 response.setContentType("text/html;charset=utf-8"); //放行 chain.doFilter(request, response); } /** * 过滤器初始化的时候调用 */ public void init(FilterConfig fConfig) throws ServletException { } }
package cn.userLogin.filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.annotation.WebFilter; /** * 这个过滤器进行参数的格式检查 */ public class ParamFilter implements Filter { public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //检查参数的格式 String uName = request.getParameter("uname"); String uPassword = request.getParameter("upass"); if(uName == null || uPassword == null || uName.length()==0 || uPassword.length()==0){ response.getWriter().append("你的参数格式不正常"); return;//退出方法 } chain.doFilter(request, response); } /** * @see Filter#init(FilterConfig) */ public void init(FilterConfig fConfig) throws ServletException { // TODO Auto-generated method stub } }
Filter过滤器的分界方法chain.doFilter(request,response)
上面的图片也需给的并不是非常准确,因为在用户请求到服务的时候会经过过滤器,在浏览器响应到服务器的时候也会进行过滤器的。在用户请求到服务器的时候,执行的代码就是 chain.doFilter(request, response); 之前的代码,在服务器响应浏览器的时候执行就是 chain.doFilter(request, response); 之后的代码。
比如:
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { System.out.println("before"); chain.doFilter(request, response); System.out.println("after"); }
我们可以看出chain.doFilter(request,response)是一个分界方法,之前的代码对应请求,之后的代码对应响应。
因此如果我们在使用的时候不指定chain.doFilter(request,response)的话,这样请求是不能到达服务器的,因此我们可以在filter组件中对请求的用户做一些处理,比如上面的案例。