首页 > 代码库 > Servlet学习笔记（八）—— 自定义过滤器的编写改进：自定义实现FilterChain
Servlet学习笔记（八）—— 自定义过滤器的编写改进：自定义实现FilterChain
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，但是有个缺陷就是，限定了过滤顺序，而不能实现先进行request过滤，最后response过滤，并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的执行顺序在这篇博文中得到很仔细的讲解，总结一点，多个过滤器的执行顺序是根据web.xml中不同<filter-mapping>的顺序来先后执行的，比如：
<?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> 将会先执行secondFilter，再执行firstFilter。
下面是截取的一段实现Filter接口的doFilter代码，用户自定义的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() ..");
} 可以看到第四行的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。不是一下子全部初始化所有的Filter对象。
依据这个思想，我自己定义了一个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可以自行定义，以后想更改过滤顺序只要改这个String数组就可以。
相应的其他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{
@Override
public void init() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest reuqest, ServletResponse response,FilterChain fc)throws InstantiationException, IllegalAccessException, Exception{
// TODO Auto-generated method stub
reuqest.setCharacterEncoding("UTF-8");
fc.doFilter(reuqest, response,fc);
response.setContentType("text/html;charset=UTF-8");
}
@Override
public 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(){}
@Override
public void init() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest reuqest, ServletResponse response,FilterChain fc)
throws Exception {
// TODO Auto-generated method stub
HttpServletRequest 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，不能直接是执行下一个Filter,因为如果未登陆，
那么敏感词过滤就不必再做，而且可以尝试不加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执行。
}
}
@Override
public 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();
}
}
@Override
public void init() {
// TODO Auto-generated method stub
}
@Override
public 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);
}
@Override
public 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 stub
Filter filter=new EncodingFilter();
FilterChain fc=new FilterChain();
try {
filter.doFilter(request, response,fc);
} catch (Exception e) {
// TODO Auto-generated catch block
e.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>");
}
}
自定义过滤器链的编写这个是源码的下载地址。
希望大家多多指教~~
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