java中常用的Filter

一、字符编码的过滤器 

package com.zhaokuo.filter;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * @author 赵阔 2012-6-11
 * 
 * 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 extends AbstractFilter {
	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 

package com.zhaokuo.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.http.HttpServletResponse;

/**
 * @author 赵阔 2012-6-11 
 * 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 

package com.test.filter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

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;
import javax.servlet.http.HttpSession;

/**
 * @author 赵阔 2012-6-11
 *  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 com.test.filter;

import java.io.IOException;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

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 org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * @author 赵阔 2012-6-11
 *
 */
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：

package com.test.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.http.HttpServletRequest;

/**
 * @author 赵阔 2012-6-11
 * 
 */
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。