笔记六中实现了三种过滤器：字符编码过滤、登录权限过滤、敏感词过滤，可是有个缺陷就是，限定了过滤顺序，而不能实现先进行request过滤。最后response过滤，而且中间几项过滤的顺序不能动态改变。所以这里做个改进。实现一个过滤顺序的FilterChain。

多个Filter的运行顺序在这篇博文中得到非常细致的解说，总结一点。多个过滤器的运行顺序是依据web.xml中不同<filter-mapping>的顺序来先后运行的，比方：

<?xml version="1.0" encoding="UTF-8"?

> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>firstFilter</filter-name> <filter-class>com.test.filter.FirstFilter</filter-class> </filter> <filter> <filter-name>secondFilter</filter-name> <filter-class>com.test.filter.SecondFilter</filter-class> </filter> <filter-mapping> <filter-name>secondFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter-mapping> <filter-name>firstFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <servlet> <servlet-name>firstServlet</servlet-name> <servlet-class>com.alimama.servlet.FirstServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>firstServlet</servlet-name> <url-pattern>/firstServlet</url-pattern> </servlet-mapping> </web-app>

将会先运行secondFilter，再运行firstFilter。

以下是截取的一段实现Filter接口的doFilter代码，用户自己定义的Filter都实现了这个接口：

 public void doFilter(ServletRequest request, ServletResponse response,   FilterChain chain) throws IOException, ServletException {   System.out.println("before invoke secondFilter's chain.doFilter() ..");   chain.doFilter(request, response);   System.out.println("after invoke secondFilter's chain.doFilter() ..");   }   

能够看到第四行的chain.doFilter(request,response);这句代码是Servlet里的Filter技术的核心，它的主要职能是将请求传递给下一个Filter。

不是一下子所有初始化所有的Filter对象。

根据这个思想，我自定义了一个FilterChain来实现多个过滤器的过滤顺序。

//FilterChain.java
package lewa;import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class FilterChain {//private static final String[] filters={"LoginFilter","WordFilter"};private static final Filter[] filters={new LoginFilter(),new WordFilter()};private static int count=0;public void doFilter(ServletRequest request,ServletResponse response,FilterChain fc) throws InstantiationException, IllegalAccessException, Exception{if(count<filters.length){ //Class<Filter> cls=(Class<Filter>)Class.forName(filters[count]);//cls.doFilter(request, response);filters[count++].doFilter(request, response, fc);}}
}

静态成员变量filters里的过滤器实例的顺序能够自行定义，以后想更改过滤顺序仅仅要改这个String数组就能够。

对应的其它Filter也做了更改：

//Filter.java
package lewa;import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public interface Filter {public void init();public void doFilter(ServletRequest reuqest,ServletResponse response,FilterChain fc)throws Exception;public void destroy();
}

//EncodingFilter.java
package lewa;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class EncodingFilter implements Filter{@Overridepublic void init() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest reuqest, ServletResponse response,FilterChain fc)throws InstantiationException, IllegalAccessException, Exception{// TODO Auto-generated method stubreuqest.setCharacterEncoding("UTF-8");fc.doFilter(reuqest, response,fc);response.setContentType("text/html;charset=UTF-8");}@Overridepublic void destroy() {// TODO Auto-generated method stub      }}

//LoginFilter.java
package lewa;import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;public class LoginFilter implements Filter{public LoginFilter(){}@Overridepublic void init() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest reuqest, ServletResponse response,FilterChain fc)throws  Exception {// TODO Auto-generated method stubHttpServletRequest req=(HttpServletRequest)reuqest;HttpServletResponse resp=(HttpServletResponse)response;HttpSession session=req.getSession();if(session.getAttribute("username")==null){resp.sendRedirect("login.html");}else{fc.doFilter(reuqest, response,fc);//这里必须有一个else，不能直接是运行下一个Filter,由于假设未登陆。
那么敏感词过滤就不必再做，并且能够尝试不加else，你会发现。未登陆前留言会跳转到登陆界面。登陆之后再回到留言界面。
这时候count已经不满足count<filters.length,所以此时敏感词过滤将不会运行。 }}@Overridepublic void destroy() {// TODO Auto-generated method stub}}

//WordFilter.java
package lewa;import java.io.IOException;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Properties;
import java.util.regex.Matcher;
import java.util.regex.Pattern;import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class WordFilter implements Filter{private static Pattern pattern=null;public static String str=null;private void loadKeyWordProperties(){StringBuffer patternBuffer = new StringBuffer();try{InputStream in =WordFilter.class.getClassLoader().getResourceAsStream("words.properties");Properties properties = new Properties();properties.load(in);Enumeration<?> enu=properties.propertyNames();while(enu.hasMoreElements()){patternBuffer.append((String)enu.nextElement()+"|");}patternBuffer.deleteCharAt(patternBuffer.length()-1);pattern = Pattern.compile(new String(patternBuffer.toString().getBytes("ISO-8859-1"),"UTF-8"));}catch(IOException e){e.printStackTrace();}}@Overridepublic void init() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest reuqest, ServletResponse response,FilterChain fc)throws InstantiationException, IllegalAccessException, Exception {// TODO Auto-generated method stub     loadKeyWordProperties();str=reuqest.getParameter("liuyan");try{Matcher m=pattern.matcher(str);str=m.replaceAll("**");}catch(Exception e){e.printStackTrace();}       fc.doFilter(reuqest, response,fc);}@Overridepublic void destroy() {// TODO Auto-generated method stub}
}

最后Servlet里的代码更改：

package lewa;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;/*** Servlet implementation class Summary*/
public class Summary extends HttpServlet {private static final long serialVersionUID = 1L;/*** @see HttpServlet#HttpServlet()*/public Summary() {super();// TODO Auto-generated constructor stub}/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)*/protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubFilter filter=new EncodingFilter();FilterChain  fc=new FilterChain();try {filter.doFilter(request, response,fc);} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}PrintWriter out=response.getWriter();HttpSession session=request.getSession();String name=(String) session.getAttribute("username");if(name!=null&&!"".equals(name)) {name=new String(name.getBytes("ISO-8859-1"),"UTF-8");}out.println("<html><head><title>留言板内容</title></head><body>");out.println("用户名："+name);out.println("<br/>"+WordFilter.str+"</body></html>");        }
}

自己定义过滤器链的编写这个是源代码的下载地址。

希望大家多多不吝赐教~~