servlet 过滤器(Filter)（八）

1.servlet过滤器产生背景

　　项目中我们会遇到这样一类的需求，对访问服务器的用户ip实施过滤，只有在允许名单中的ip才能访问服务，为了实现需求，每当有客户端请求时，我们都会写校验ip的代码，客户端能够访问到的servlet我们都需要这样做，很明显这样做有一个缺点，就是代码冗余，维护不方便，如果验证规则改变，修改起来也特别麻烦。

　　为了解决以上问题，Filter 技术应运而生。

2.servlet过滤器是什么？

　　servlet过滤器是在java servlet 2.3 中定义的。它能够对servlet容器传给servlet组件的ServletRequest 对象和 ServletResponse对象进行检查和修改。

3.案例

　　所有servlet过滤器都要实现javax.servlet.Filter接口。

　　NoteFilter

package com.learn;import javax.servlet.*;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;/** * Created by Administrator on 2017/09/29. */public class NoteFilter implements Filter { private FilterConfig config = null; private String ipTable = null; //ip名单 @Override public void init(FilterConfig filterConfig) throws ServletException {  System.out.println("note filter initial");  this.config = filterConfig;  this.ipTable = config.getInitParameter("ipTable"); } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {  System.out.println("do filter starting");  //校验ip地址  if(!veryfyIP(request,response))   return;  long befor = System.currentTimeMillis();  config.getServletContext().log("before call note Filter");  chain.doFilter(request,response);  config.getServletContext().log("after call note Filter");  long after = System.currentTimeMillis();  String name ="";  if(request instanceof HttpServletRequest){   name = ((HttpServletRequest) request).getRequestURI();  }  config.getServletContext().log("Note Filter : name:"+name +" time :"+(after -befor)+"ms"); } @Override public void destroy() { } private boolean veryfyIP(ServletRequest request, ServletResponse response){  String ip = request.getRemoteAddr();  System.out.println("请求ip:"+ip);  System.out.println("ipTable 黑名单:"+ipTable);  if(ip.indexOf(ipTable) == -1){   System.out.println("校验不通过");   response.setContentType("text/html");   PrintWriter out = null;   try {    out = response.getWriter();    out.print("<h1>对不起，你的ip不能访问服务器</h1>");    out.flush();    out.close();   } catch (IOException e) {    e.printStackTrace();   }   return false;  } else {   return true;  } }}

NoteServlet

package com.learn;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * Created by Administrator on 2017/09/29. */public class NoteServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  System.out.println("已经通过了过滤器"); }}

web.

<filter>  <filter-name>ip</filter-name>  <filter-class>com.learn.NoteFilter</filter-class>  <init-param>   <param-name>ipTable</param-name>   <param-value>127.0.0.1</param-value>  </init-param> </filter> <filter-mapping>  <filter-name>ip</filter-name>  <url-pattern>/note</url-pattern> </filter-mapping>

<servlet>  <servlet-name>note</servlet-name>  <servlet-class>com.learn.NoteServlet</servlet-class> </servlet> <servlet-mapping>  <servlet-name>note</servlet-name>  <url-pattern>/note</url-pattern> </servlet-mapping>

结果如下：