过滤器可以简单的理解为“取你所想取”，过滤器关注的是web请求；拦截器可以简单的理解为“拒你所想拒”，拦截器关注的是方法调用，比如拦截
敏感词汇。
4.1，拦截器是基于java反射机制来实现的，而过滤器是基于函数回调来实现的。（有人说，拦截器是基于动态代理来实现的）
4.2，拦截器不依赖servlet容器，过滤器依赖于servlet容器。
4.3，拦截器只对Action起作用，过滤器可以对所有请求起作用。
4.4，拦截器可以访问Action上下文和值栈中的对象，过滤器不能。
4.5，在Action的生命周期中，拦截器可以多次调用，而过滤器只能在容器初始化时调用一次。
过滤器的应用实例
java 代码
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;
}*/
}
}
拦截器实例
1.是否登录验证
2.上载的时候先往状态表里面添加一条记录。