四个有用的过滤器（Filter）_pt 2-filter-优快云博客

本文介绍如何通过实现浏览器不缓存页面的过滤器、检测用户是否已登录的过滤器、设置HTTP请求字符编码的过滤器以及资源保护过滤器，来提升网站的安全性和用户体验。重点在于使用这些过滤器来解决页面缓存、用户认证、中文字符编码问题及资源访问权限控制等问题。

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参考：http://www.blogjava.net/fantasy/archive/2006/03/21/36593.html

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;
}*/
}
}