Java Filter 过滤器详细介绍及实例代码

public void init(FilterConfig filterConfig) throws ServletException;//初始化

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException;//拦截请求

public void destroy();//销毁

String getFilterName();//得到filter的名称。 
String getInitParameter(String name);//返回在部署描述中指定名称的初始化参数的值。如果不存在返回null. 
Enumeration getInitParameterNames();//返回过滤器的所有初始化参数的名字的枚举集合。 
public ServletContext getServletContext();//返回Servlet上下文对象的引用。

<filter>
 <filter-name>SessionFilter</filter-name>
 <filter-class>com.action.login.SessionFilter</filter-class>
 <init-param>
  <param-name>logonStrings</param-name><!-- 对登录页面不进行过滤 -->
  <param-value>/project/index.jsp;login.do</param-value>
 </init-param>
 <init-param>
  <param-name>includeStrings</param-name><!-- 只对指定过滤参数后缀进行过滤 -->
  <param-value>.do;.jsp</param-value>
 </init-param>
 <init-param>
  <param-name>redirectPath</param-name><!-- 未通过跳转到登录界面 -->
  <param-value>/index.jsp</param-value>
 </init-param>
 <init-param>
  <param-name>disabletestfilter</param-name><!-- Y:过滤无效 -->
  <param-value>N</param-value><!-- http://www.manongjc.com/article/1613.html -->
 </init-param>
</filter>
<filter-mapping>
 <filter-name>SessionFilter</filter-name>
 <url-pattern>/*</url-pattern>
</filter-mapping>

package com.action.login;
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;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
/**
 * 判断用户是否登录,未登录则退出系统
 * http://www.manongjc.com/article/1613.html 
 */
public class SessionFilter implements Filter {

 public FilterConfig config;

 public void destroy() {
  this.config = null;
 }

 public static boolean isContains(String container, String[] regx) {
  boolean result = false;
  for (int i = 0; i < regx.length; i++) {
   if (container.indexOf(regx[i]) != -1) {
    return true;
   }
  }
  return result;
 }
 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
  HttpServletRequest hrequest = (HttpServletRequest)request;
  HttpServletResponseWrapper wrapper = new HttpServletResponseWrapper((HttpServletResponse) response);

  String logonStrings = config.getInitParameter("logonStrings");  // 登录登陆页面
  String includeStrings = config.getInitParameter("includeStrings"); // 过滤资源后缀参数
  String redirectPath = hrequest.getContextPath() + config.getInitParameter("redirectPath");// 没有登陆转向页面
  String disabletestfilter = config.getInitParameter("disabletestfilter");// 过滤器是否有效

  if (disabletestfilter.toUpperCase().equals("Y")) { // 过滤无效
   chain.doFilter(request, response);
   return;
  }
  String[] logonList = logonStrings.split(";");
  String[] includeList = includeStrings.split(";");

  if (!this.isContains(hrequest.getRequestURI(), includeList)) {// 只对指定过滤参数后缀进行过滤
   chain.doFilter(request, response);
   return;
  }

  if (this.isContains(hrequest.getRequestURI(), logonList)) {// 对登录页面不进行过滤
   chain.doFilter(request, response);
   return;
  }

  String user = ( String ) hrequest.getSession().getAttribute("useronly");//判断用户是否登录
  if (user == null) {
   wrapper.sendRedirect(redirectPath);
   return;
  }else {
   chain.doFilter(request, response);
   return;
  }
 }
 public void init(FilterConfig filterConfig) throws ServletException {
  config = filterConfig;
 }
}

<filter>
 <filter-name>encoding</filter-name>
 <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
 <init-param>
  <param-name>encoding</param-name><!--用来指定一个具体的字符集-->
  <param-value>UTF-8</param-value>
 </init-param>
 <init-param>
  <param-name>forceEncoding</param-name><!--true：无论request是否指定了字符集，都是用encoding；false：如果request已指定一个字符集，则不使用encoding-->
  <param-value>false</param-value>
 </init-param>
</filter>
<filter-mapping>
 <filter-name>encoding</filter-name>
 <url-pattern>/*</url-pattern>
</filter-mapping>

<filter><!-- lazy loading enabled in spring -->
 <filter-name>OpenSessionInViewFilter</filter-name>
 <filter-class>org.springframework.orm.hibernate3.support.OpenSessionInViewFilter</filter-class>
 <init-param>
  <param-name>sessionFactoryBeanName</param-name><!-- 可缺省。默认是从spring容器中找id为sessionFactory的bean，如果id不为sessionFactory，则需要配置如下，此处SessionFactory为spring容器中的bean。 -->
  <param-value>sessionFactory</param-value>
 </init-param>
 <init-param>
  <param-name>singleSession</param-name><!-- singleSession默认为true,若设为false则等于没用OpenSessionInView -->
  <param-value>true</param-value>
 </init-param>
</filter>
<filter-mapping>
 <filter-name>OpenSessionInViewFilter</filter-name>
 <url-pattern>*.do</url-pattern>
</filter-mapping>
 

<!-- struts 2.x filter -->
<filter>
 <filter-name>struts2</filter-name>
 <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
 <filter-name>struts2</filter-name>
 <url-pattern>*.do</url-pattern>
</filter-mapping>