初识过滤器
1，这里写的功能是 登录功能 。从login.jsp页面输入用户名，然后判断输入的用户名对不对，如果对了那么跳转到JSP包地下的 index.jsp页面。
login.jsp页面代码如下：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'login.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="${pageContext.request.contextPath }/servlet/LoginServlet" method="post">
<input type="text" name="uname"/>
<input type="submit" value="登录"/>
</form>
</body>
</html>
index.jsp页面代码如下：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<h2>index</h2>
</body>
</html>
1.1 这里我们定义 servlet 层的 LoginServlet 来接收请求和响应。
LoginServlet 代码如下：
ckage cn.happy.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginServlet extends HttpServlet {
/**
*
*王志亭
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request,response);
}
/**
* 王志亭
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String uname = request.getParameter("uname");
if("admin".equals(uname)){
//request.getSession().setAttribute("uname", uname);
request.getRequestDispatcher("/JSP/index.jsp").forward(request, response);
}else{
request.getRequestDispatcher("/login.jsp").forward(request, response);
}
}
}
1.2那么问题来了，如果有个人知道了访问页面 index.jsp的路径 那么不用登录也能反问。所以为了避免这个情况 有了 过滤Filter。
在 myeclipse 这款软件里头没有 Filter 这个过滤器模版，所以使用 类实现Filter接口 类转换成过滤器的方法。
过滤器的代码如下：
package cn.happy.filter;
import java.io.IOException;
import java.util.regex.Pattern;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SessionFilter implements Filter{
Pattern pattern;
@Override
public void init(FilterConfig Config) throws ServletException {
//我们配置了例外的过滤器不该走的servlet
String url = Config.getInitParameter("unFilter");
if(url!=null&&!"".equals(url)){
pattern= Pattern.compile(url);
}
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//因为ServletRequest和ServletResponse里头没有Session,所以我们抢转成他的子接口HttpServletRequest
HttpServletRequest req=(HttpServletRequest) request;
HttpServletResponse res=(HttpServletResponse) response;
String path = req.getServletPath();
if(pattern.matcher(path).matches()){
chain.doFilter(request, response); return;
}
Object obj = req.getSession().getAttribute("uname");
if(obj!=null){ //已经登录过
chain.doFilter(request, response);
}else{
res.sendRedirect(req.getContextPath()+"/login.jsp");
}
}
@Override
public void destroy() {
}
}
因为没有 filter 的模版，所以我们在 web.xml文档中自己配置相关的 代码：
<?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" id="WebApp_ID" version="3.0">
<display-name></display-name>
<filter>
<filter-name>SessionFilter</filter-name>
<filter-class>cn.happy.filter.SessionFilter</filter-class>
<init-param>
<param-name>unFilter</param-name>
<param-value>/servlet/(Login|Register)Servlet</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>SessionFilter</filter-name>
<url-pattern>/JSP/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>SessionFilter</filter-name>
<url-pattern>/servlet/*</url-pattern>
</filter-mapping>
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>cn.happy.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/servlet/LoginServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
