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>