2.過濾器

時間 2019-12-06

標籤過濾器简体版

原文原文鏈接

1. 什麼是過濾器html

過濾器是一個運行在服務器端的程序，先於與之相關的servlet或JSP頁面以前運行實現對請求資源的過濾的功能；前端

過濾器可附加到一個或多個servlet或jsp頁面上，能夠檢查請求信息也能夠處理相應信息；java

filter的基本功能是對Servlet容器調用Servlet的過程進行攔截，從而在Servlet執行先後實現一些特殊的功能。web

如圖，瀏覽器發出的請求先遞交給第一個filter進行過濾，符合規則則放行，遞交給filter鏈中的下一個過濾器進行過濾。過濾器在鏈中的順序與它在web.xml中配置的順序有關，配置在前的則位於鏈的前端。當請求經過了鏈中全部過濾器後就能夠訪問資源文件了，若是不能經過，則可能在中間某個過濾器中被處理掉。瀏覽器

在doFilter（）方法中，chain.doFilter()前的通常是對request執行的過濾操做，chain.doFilter後面的代碼通常是對response執行的操做。過濾鏈代碼的執行順序以下：服務器

過濾器通常用於登陸權限驗證、資源訪問權限控制、敏感詞彙過濾、字符編碼轉換等等操做，便於代碼重用，沒必要每一個servlet中還要進行相應的操做。app

2. 過濾器的編寫流程dom

實現類，須要實現接口javax.servlet.Filter；

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 
 9 public class ServletFilter extends HttpServlet {
10 
11     private static final long serialVersionUID = 1L;
12 
13     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
14         String name = (String) request.getAttribute("name");
15         System.out.println("servlet獲取request域中的name屬性="+name);
16         response.getWriter().write("hello haohao...name="+name);
17     }
18 
19     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
20         doGet(request, response);
21     }
22 }

ServletFilter

 1 package com.eagle.filter;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.Filter;
 5 import javax.servlet.FilterChain;
 6 import javax.servlet.FilterConfig;
 7 import javax.servlet.ServletException;
 8 import javax.servlet.ServletRequest;
 9 import javax.servlet.ServletResponse;
10 
11 public class Demo1Filter implements Filter {
12 
13     public Demo1Filter() {
14 
15     }
16 
17     public void init(FilterConfig fConfig) throws ServletException {
18 
19     }
20 
21     public void destroy() {
22 
23     }
24 
25     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
26             throws IOException, ServletException {
27         request.setAttribute("name", "filter");
28         System.out.println("servlet以前進行調用，設置request域的name屬性爲filter");
29         chain.doFilter(request, response);
30     }
31 }

Demo1Filter

配置，在web.xml使用<filter>和<filter-mapping>進行配置。

1 <filter>
2     <display-name>Demo1Filter</display-name>
3     <filter-name>Demo1Filter</filter-name>
4     <filter-class>com.eagle.filter.Demo1Filter</filter-class>
5   </filter>
6   <filter-mapping>
7     <filter-name>Demo1Filter</filter-name>
8     <url-pattern>/*</url-pattern>
9   </filter-mapping>

web.xml

3. 配置web.xml詳解jsp

<filter>
　　<filter-name>loginFilter</filter-name>　　　　　　　　　　//過濾器名稱
　　<filter-class>com.x.control.loginFilter</filter-class> 　　 //過濾器類的包路徑
　　<init—param> 　　　　　　　　　　　　　　　　　　　　 //可選
　　　　<param—name>參數名</param-name>　　　　　　 //過濾器初始化參數
　　　　<param-value>參數值</param-value>
　　</init—pamm>
</filter>

<filter-mapping>　　　　　　　　　　　　　　　　　　　　　//過濾器映射
　　<filter-name>loginFilter</filter-name>
　　<url-pattern>指定過濾器做用的對象</url-pattern>ide

</filter-mapping>

在配置中須要注意的有兩處：

一是<filter-class>指明過濾器類所在的包路徑。
二是<url-pattren>處定義過濾器做用的對象。通常有如下規則：

1：做用於全部web資源：<url—pattern>/*</url-pattern>。則客戶端請求訪問任意資源文件時都要通過過濾器過濾，經過則訪問文件，不然攔截。

2：做用於某一文件夾下全部文件：<url—pattern>/dir/*</url-pattern>

3：做用於某一種類型的文件：<url—pattern>*.擴展名</url-pattern>。好比<url—pattern>*.jsp</url-pattern>過濾全部對jsp文件的訪問請求。

4：做用於某一文件夾下某一類型文件：<url—pattern>/dir/*.擴展名</url-pattern>

若是一個過濾器須要過濾多種文件，則能夠配置多個<filter-mapping>，一個mapping定義一個url-pattern來定義過濾規則。

4. 過濾器實現設置字符編碼問題

編寫測試jsp

 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>Insert title here</title>
 9 </head>
10 <body>
11 <form action="${ pageContext.request.contextPath }/Login" method="post">
12     <table border="0px">
13         <tr>
14             <td>用戶名：</td>
15             <td><input type="text" name="username" id="username" placeholder="請輸入用戶名" /></td>
16         </tr>
17         <tr>
18             <td>密碼：</td>
19             <td><input type="password" name="password" id="password" placeholder="請輸入密碼" /></td>
20         </tr>
21         <tr>
22             <td colspan="2"><input type="submit" value="提交" /></td>
23         </tr>
24     </table>
25 </form>
26 </body>
27 </html>

postcharacter.jsp

編寫測試servlet

package cn.eagle.web;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Login extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println("username="+username+";password"+password);
        response.getWriter().write("hello haohao..."+"username="+username+";password"+password+"張三");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

編寫filter

 1 package cn.eagle.filter;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.Filter;
 5 import javax.servlet.FilterChain;
 6 import javax.servlet.FilterConfig;
 7 import javax.servlet.ServletException;
 8 import javax.servlet.ServletRequest;
 9 import javax.servlet.ServletResponse;
10 
11 public class MyRequestCharacterFilter implements Filter {
12 
13     public MyRequestCharacterFilter() {
14 
15     }
16 
17     public void init(FilterConfig fConfig) throws ServletException {
18 
19     }
20 
21     public void destroy() {
22 
23     }
24 
25     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
26             throws IOException, ServletException {
27         request.setCharacterEncoding("utf-8");
28         response.setCharacterEncoding("utf-8");
29         response.setContentType("text/html;charset=utf-8");
30         chain.doFilter(request, response);
31     }
32 }

MyRequestCharacterFilter

web.xml配置filter

1   <filter>
2     <display-name>MyRequestCharacterFilter</display-name>
3     <filter-name>MyRequestCharacterFilter</filter-name>
4     <filter-class>cn.eagle.filter.MyRequestCharacterFilter</filter-class>
5   </filter>
6   <filter-mapping>
7     <filter-name>MyRequestCharacterFilter</filter-name>
8     <url-pattern>/*</url-pattern>
9   </filter-mapping>

web.xml

5. 解決post和get方式亂碼問題

編寫本身的request類，該類實現HttpServletRequestWrapper，並重寫getParameter()方法；

 1 package cn.eagle.domain;
 2 
 3 import java.io.UnsupportedEncodingException;
 4 
 5 import javax.servlet.http.HttpServletRequest;
 6 import javax.servlet.http.HttpServletRequestWrapper;
 7 
 8 public class MyRequest extends HttpServletRequestWrapper {
 9 
10     public MyRequest(HttpServletRequest request) {
11         super(request);
12 
13     }
14 
15     @Override
16     public String getParameter(String name) {
17 
18         String value = super.getParameter(name);
19         try {
20             if ("GET".equalsIgnoreCase(this.getMethod())) {
21                 value = new String(value.getBytes("ISO8859-1"), "UTF-8");
22             }
23         } catch (Exception e) {
24             throw new RuntimeException();
25         }
26         return value;
27     }
28 
29 }

MyRequest

編寫filter，傳遞本身的request對象；

 1 package cn.eagle.filter;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.Filter;
 5 import javax.servlet.FilterChain;
 6 import javax.servlet.FilterConfig;
 7 import javax.servlet.ServletException;
 8 import javax.servlet.ServletRequest;
 9 import javax.servlet.ServletResponse;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 
13 import cn.eagle.domain.MyRequest;
14 
15 public class EncodingFilter implements Filter {
16 
17     public EncodingFilter() {
18 
19     }
20 
21     public void init(FilterConfig fConfig) throws ServletException {
22 
23     }
24 
25     public void destroy() {
26 
27     }
28 
29     public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
30             throws IOException, ServletException {
31         HttpServletRequest request = (HttpServletRequest) req;
32         HttpServletResponse response = (HttpServletResponse) resp;
33         // 設置編碼
34         request.setCharacterEncoding("utf-8");
35         response.setCharacterEncoding("utf-8");
36         response.setContentType("text/html;charset=utf-8");
37         // 建立自定義request
38         MyRequest myRequest = new MyRequest(request);
39         chain.doFilter(myRequest, response);
40     }
41 }

EncodingFilter

編寫servlet進行測試。

 1 package cn.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 
 9 public class Encoding extends HttpServlet {
10 
11     private static final long serialVersionUID = 1L;
12 
13     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
14         String username = request.getParameter("username");
15         System.out.println(username);
16         response.getWriter().write("hello haohao..."+username);
17     }
18 
19     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
20         doGet(request, response);
21     }
22 }

Encoding

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