一、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


{
}
}

二、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());
}
}
}
}
三、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");
}
} 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
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
{
}
}

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:
<!-- 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。