04_過濾器Filter_03_多個Filter的執行順序

【Filter鏈】

*在一個web應用中，能夠開發編寫多個Filter，這些Filter組合起來稱爲一個Filter鏈。

*web服務器根據Filter在web.xml中的註冊順序，決定先調用哪一個Filter，當第一個Filter的doFilter方法被調用時，web服務器會建立一個表明Filter鏈的FilterChain對象傳遞給該方法，在doFilter方法中，開發人員若是調用了FilterChain對象的doFilter方法，則web服務器會檢查FilterChain對象中是否還有filter，若是有，則調用第二個filter，若是沒有，則調用目標資源。

 

【工程截圖】

設計了兩個Filter和一個Servlet，訪問Servlet時，查看Filter的執行順序。

【web.xml】

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>FilterDemo01</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  
  <!-- 過濾順序：誰的寫在上面，誰先被過濾 -->
  <filter>
    <filter-name>FilterTest01</filter-name>
    <filter-class>com.Higgin.web.filter.FilterTest01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>FilterTest01</filter-name>
    <url-pattern>/*</url-pattern> <!-- 過濾全部 -->
  </filter-mapping>
  
  <filter>
    <filter-name>FilterTest02</filter-name>
    <filter-class>com.Higgin.web.filter.FilterTest02</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>FilterTest02</filter-name>
    <url-pattern>/*</url-pattern> <!-- 過濾全部 -->
  </filter-mapping>
    
</web-app>

 

【FilterTest01.java】

package com.Higgin.web.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;

public class FilterTest01 implements Filter{

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
        System.out.println("FilterTest01 執行前---");
 chain.doFilter(request, response);//讓目標資源執行，即：放行
 System.out.println("FilterTest01 執行後---");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        
    }
    
    @Override
    public void destroy() {
        
    }
}

【FilterTest02.java】

package com.Higgin.web.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;

public class FilterTest02 implements Filter{

    

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
        System.out.println("FilterTest02 執行前---"); chain.doFilter(request, response); //放行 System.out.println("FilterTest02 執行後---");
    }


    @Override
    public void init(FilterConfig arg0) throws ServletException {
        
    }
    
    @Override
    public void destroy() {
        
    }

}

 

【ServletTest01.java】

package com.Higgin.web.servlet;

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

/**
 * Servlet implementation class ServletTest01
 */
@WebServlet("/ServletTest01")
public class ServletTest01 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public ServletTest01() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //response.getWriter().write("中國 加油！China Come on!");
        System.out.println("執行ServletTest01---");
    }

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

}

【運行結果】

在瀏覽器中輸入：http://localhost:8080/FilterDemo01/ServletTest01

查看控制檯輸出結果

 

本身能夠嘗試分別註釋FilterTest01和FilterTest02中的chain.doFilter方法，用Junit查看具體的執行過程。