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過濾器生命周期

• web應(yīng)用程序啟動時(shí)，web服務(wù)器創(chuàng)建Filter實(shí)例對象，以及對象初始化操作
• 當(dāng)請求訪問與過濾器關(guān)聯(lián)的Web資源時(shí)，過濾器攔截請求，完成指定功能。
• Fliter對象創(chuàng)建后會駐留在內(nèi)存，在web應(yīng)用移除或者服務(wù)器停止時(shí)才銷毀
• 過濾器的創(chuàng)建和銷毀由web服務(wù)器負(fù)責(zé)

過濾器實(shí)現(xiàn)步驟

1、編寫java類實(shí)現(xiàn)Fliter接口，并實(shí)現(xiàn)其doFilter方法
2、在web.xml文件中對Fliter類進(jìn)行注冊，并設(shè)置所攔截的資源。

過濾器鏈

• 在一個(gè)web應(yīng)用中，多個(gè)過濾器組合起來稱之為一個(gè)過濾器鏈
• 過濾器的調(diào)用順序取決于過濾器在web.xml文件中的注冊順序
• 案例1 中文亂碼過濾器實(shí)現(xiàn)
• web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>FilterDemoWebProj</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <!-- 字符亂碼過濾器配置 -->
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.alan.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>systemName</param-name>
      <param-value>filter Encoding</param-value>
    </init-param>
    <init-param>
      <param-name>version</param-name>
      <param-value>1.0</param-value>
    </init-param>
    <init-param>
      <param-name>charSet</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!-- 安全控制過濾器配置 -->
  <filter>
    <filter-name>SessionFilter</filter-name>
    <filter-class>com.alan.filter.SessionFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>SessionFilter</filter-name>
    <url-pattern>/message.jsp</url-pattern>
  </filter-mapping>
</web-app>

• filter 中文亂碼

package com.alan.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CharacterEncodingFilter implements Filter {

    //定義FilterConfig對象，將init傳入的config對其賦值
    private FilterConfig config;
    
    
    public CharacterEncodingFilter() {
        // TODO Auto-generated constructor stub
    }

    public void destroy() {     
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

//      String systemName = config.getInitParameter("systemName");
//      String version = config.getInitParameter("version");
//      System.out.println(systemName);
//      System.out.println(version);
        
        //中文編碼過濾器實(shí)現(xiàn)
        String charSet = config.getInitParameter("charSet");
        request.setCharacterEncoding(charSet);

            //此方法通知web服務(wù)器，連接請求已經(jīng)執(zhí)行完成
            chain.doFilter(request, response);

    }

    public void init(FilterConfig fConfig) throws ServletException {
        this.config = fConfig;
        
    }
}

• filter 安全控制

package com.alan.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SessionFilter implements Filter {

    public SessionFilter() {

    }

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        // 用戶登陸安全控制
        // 1、向下轉(zhuǎn)型
        HttpServletRequest hresquest = (HttpServletRequest) request;
        HttpServletResponse hresponse = (HttpServletResponse) response;
        // 2、判斷全局域中的username是否有值
        String username = (String) hresquest.getServletContext().getAttribute("username");
        if (username == null) {
            hresponse.sendRedirect(hresquest.getContextPath() + "/index.jsp?flag=1");
            return;

        } else { // 此方法通知web服務(wù)器，連接請求已經(jīng)執(zhí)行完成
            chain.doFilter(request, response);
            return;
        }
    }

    public void init(FilterConfig fConfig) throws ServletException {

    }

}

dispatcher子元素

• <dispatcher></dispatcher>沒有配置，默認(rèn)為request
• 包括 request include forward error 四種配置方式
• 如果是重定向的話 需要配置為request？？？
• 可以對一個(gè)過濾器配置多個(gè)dispatcher子元素