(转)Servlet过滤器

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Servlet JSF 浏览器 Cache Apache

一、字符编码的过滤器

import javax.servlet.*; 
import java.io.IOException; 

/** *//** 
* 用于设置 HTTP 请求字符编码的过滤器，通过过滤器参数encoding指明使用何种字符编码,用于处理Html Form请求参数的中文问题 
*/ 
public class CharacterEncodingFilter 
implements Filter 
{ 
protected FilterConfig filterConfig = null; 
protected String encoding = ""; 

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
{ 
if(encoding != null) 
servletRequest.setCharacterEncoding(encoding); 
filterChain.doFilter(servletRequest, servletResponse); 
} 

public void destroy() 
{ 
filterConfig = null; 
encoding = null; 
} 

public void init(FilterConfig filterConfig) throws ServletException 
{ 
this.filterConfig = filterConfig; 
this.encoding = filterConfig.getInitParameter("encoding"); 

} 
}

二、使浏览器不缓存页面的过滤器

import javax.servlet.*; 
import javax.servlet.http.HttpServletResponse; 
import java.io.IOException; 

/** *//** 
* 用于的使 Browser 不缓存页面的过滤器 
*/ 
public class ForceNoCacheFilter implements Filter { 

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException 
{ 
((HttpServletResponse) response).setHeader("Cache-Control","no-cache"); 
((HttpServletResponse) response).setHeader("Pragma","no-cache"); 
((HttpServletResponse) response).setDateHeader ("Expires", -1); 
filterChain.doFilter(request, response); 
} 

public void destroy() { 
} 

public void init(FilterConfig filterConfig) throws ServletException { 
} 
}

三、检测用户是否登陆的过滤器

import javax.servlet.*; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import javax.servlet.http.HttpSession; 
import java.util.List; 
import java.util.ArrayList; 
import java.util.StringTokenizer; 
import java.io.IOException; 

/** *//** 
* 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面 


* 配置参数 


* checkSessionKey 需检查的在 Session 中保存的关键字 

* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath 

* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath 

*/ 
public class CheckLoginFilter 
implements Filter 
{ 
protected FilterConfig filterConfig = null; 
private String redirectURL = null; 
private List notCheckURLList = new ArrayList(); 
private String sessionKey = null; 

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
{ 
HttpServletRequest request = (HttpServletRequest) servletRequest; 
HttpServletResponse response = (HttpServletResponse) servletResponse; 

HttpSession session = request.getSession(); 
if(sessionKey == null) 
{ 
filterChain.doFilter(request, response); 
return; 
} 
if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null) 
{ 
response.sendRedirect(request.getContextPath() + redirectURL); 
return; 
} 
filterChain.doFilter(servletRequest, servletResponse); 
} 

public void destroy() 
{ 
notCheckURLList.clear(); 
} 

private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) 
{ 
String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo()); 
return notCheckURLList.contains(uri); 
} 

public void init(FilterConfig filterConfig) throws ServletException 
{ 
this.filterConfig = filterConfig; 
redirectURL = filterConfig.getInitParameter("redirectURL"); 
sessionKey = filterConfig.getInitParameter("checkSessionKey"); 

String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList"); 

if(notCheckURLListStr != null) 
{ 
StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";"); 
notCheckURLList.clear(); 
while(st.hasMoreTokens()) 
{ 
notCheckURLList.add(st.nextToken()); 
} 
} 
} 
}

四、资源保护过滤器

package catalog.view.util; 

import javax.servlet.Filter; 
import javax.servlet.FilterConfig; 
import javax.servlet.ServletRequest; 
import javax.servlet.ServletResponse; 
import javax.servlet.FilterChain; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServletRequest; 
import java.io.IOException; 
import java.util.Iterator; 
import java.util.Set; 
import java.util.HashSet; 
// 
import org.apache.commons.logging.Log; 
import org.apache.commons.logging.LogFactory; 

/** *//** 
* This Filter class handle the security of the application. 
* 
* It should be configured inside the web.xml. 
* 
* @author Derek Y. Shen 
*/ 
public class SecurityFilter implements Filter { 
//the login page uri 
private static final String LOGIN_PAGE_URI = "login.jsf"; 

//the logger object 
private Log logger = LogFactory.getLog(this.getClass()); 

//a set of restricted resources 
private Set restrictedResources; 

/** *//** 
* Initializes the Filter. 
*/ 
public void init(FilterConfig filterConfig) throws ServletException { 
this.restrictedResources = new HashSet(); 
this.restrictedResources.add("/createProduct.jsf"); 
this.restrictedResources.add("/editProduct.jsf"); 
this.restrictedResources.add("/productList.jsf"); 
} 

/** *//** 
* Standard doFilter object. 
*/ 
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) 
throws IOException, ServletException { 
this.logger.debug("doFilter"); 

String contextPath = ((HttpServletRequest)req).getContextPath(); 
String requestUri = ((HttpServletRequest)req).getRequestURI(); 

this.logger.debug("contextPath = " + contextPath); 
this.logger.debug("requestUri = " + requestUri); 

if (this.contains(requestUri, contextPath) && !this.authorize((HttpServletRequest)req)) { 
this.logger.debug("authorization failed"); 
((HttpServletRequest)req).getRequestDispatcher(LOGIN_PAGE_URI).forward(req, res); 
} 
else { 
this.logger.debug("authorization succeeded"); 
chain.doFilter(req, res); 
} 
} 

public void destroy() {} 

private boolean contains(String value, String contextPath) { 
Iterator ite = this.restrictedResources.iterator(); 

while (ite.hasNext()) { 
String restrictedResource = (String)ite.next(); 

if ((contextPath + restrictedResource).equalsIgnoreCase(value)) { 
return true; 
} 
} 

return false; 
} 

private boolean authorize(HttpServletRequest req) { 

//处理用户登录 
/**//* UserBean user = (UserBean)req.getSession().getAttribute(BeanNames.USER_BEAN); 

if (user != null && user.getLoggedIn()) { 
//user logged in 
return true; 
} 
else { 
return false; 
}*/ 
} 
}

五利用Filter限制用户浏览权限

在一个系统中通常有多个权限的用户。不同权限用户的可以浏览不同的页面。使用Filter进行判断不仅省下了代码量，而且如果要更改的话只需要在Filter文件里动下就可以。
以下是Filter文件代码：

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.http.HttpServletRequest; 

public class RightFilter implements Filter { 

public void destroy() { 

} 

public void doFilter(ServletRequest sreq, ServletResponse sres, FilterChain arg2) throws IOException, ServletException { 
// 获取uri地址 
HttpServletRequest request=(HttpServletRequest)sreq; 
String uri = request.getRequestURI(); 
String ctx=request.getContextPath(); 
uri = uri.substring(ctx.length()); 
//判断admin级别网页的浏览权限 
if(uri.startsWith("/admin")) { 
if(request.getSession().getAttribute("admin")==null) { 
request.setAttribute("message","您没有这个权限"); 
request.getRequestDispatcher("/login.jsp").forward(sreq,sres); 
return; 
} 
} 
//判断manage级别网页的浏览权限 
if(uri.startsWith("/manage")) { 
//这里省去 
} 
} 
//下面还可以添加其他的用户权限，省去。 

} 

public void init(FilterConfig arg0) throws ServletException { 

} 

} 

<!-- 判断页面的访问权限 --> 
<filter> 
<filter-name>RightFilter</filter-name> 
<filter-class>cn.itkui.filter.RightFilter</filter-class> 
</filter> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/admin/**//*</url-pattern> 
</filter-mapping> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/manage/*</url-pattern> 
</filter-mapping> 

在web.xml中加入Filter的配置，如下： 
<filter> 

<filter-name>EncodingAndCacheflush</filter-name> 
<filter-class>EncodingAndCacheflush</filter-class> 
<init-param> 
<param-name>encoding</param-name> 
<param-value>UTF-8</param-value> 
</init-param> 
</filter> 
<filter-mapping> 
<filter-name>EncodingAndCacheflush</filter-name> 
<url-pattern>/*</url-pattern> 
</filter-mapping> 

要传递参数的时候最好使用form进行传参，如果使用链接的话当中文字符的时候过滤器转码是不会起作用的，还有就是页面上 

form的method也要设置为post，不然过滤器也起不了作用。

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