servlet過濾器(Filter)詳解（九）

更新時間：2017年09月30日 14:58:26 作者：柳暗花明睡一覺

這篇文章主要為大家詳細介紹了servlet過濾器Filter的相關資料，具有一定的參考價值，感興趣的小伙伴們可以參考一下

本文實例為大家分享了servlet過濾器的具體代碼，供大家參考，具體內容如下

1.servlet過濾器產生背景

　　項目中我們會遇到這樣一類的需求，對訪問服務器的用戶ip實施過濾，只有在允許名單中的ip才能訪問服務，為了實現(xiàn)需求，每當有客戶端請求時，我們都會寫校驗ip的代碼，客戶端能夠訪問到的servlet我們都需要這樣做，很明顯這樣做有一個缺點，就是代碼冗余，維護不方便，如果驗證規(guī)則改變，修改起來也特別麻煩。

　　為了解決以上問題，F(xiàn)ilter 技術應運而生。

2.servlet過濾器是什么？

　　servlet過濾器是在java servlet 2.3 中定義的。它能夠對servlet容器傳給servlet組件的ServletRequest 對象和 ServletResponse對象進行檢查和修改。

3.案例

　　所有servlet過濾器都要實現(xiàn)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名單


 @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");

  //校驗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("請求ip:"+ip);
  System.out.println("ipTable 黑名單:"+ipTable);

  if(ip.indexOf(ipTable) == -1){
   System.out.println("校驗不通過");
   response.setContentType("text/html");
   PrintWriter out = null;
   try {
    out = response.getWriter();
    out.print("<h1>對不起，你的ip不能訪問服務器</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("已經(jīng)通過了過濾器");


 }
}

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>

結果如下：