servlet过滤器(Filter)详解（九）

本文实例为大家分享了servlet过滤器的具体代码，供大家参考，具体内容如下

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.xml配置

<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：

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。