chain.doFilter(request, response)的简单介绍

最新推荐文章于 2025-07-10 18:01:47 发布

原创最新推荐文章于 2025-07-10 18:01:47 发布 · 1.6k 阅读

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#Servlet

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1.创建一个Servlet

FirstServlet.java

package com.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FirstServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		System.out.println("FirstServlet's doGet.");
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.println("<html>" + "<head>" + "<title>First Servlet</title>"
				+ "</head>" + "<body>" + "<h1>" + "  Hello world!" + "</h1>"
				+ "</body>" + "</html>");
	}

}

2.创建2个Filter

SecondFilter.java

package com.servlet;

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 SecondFilter implements Filter {

	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		System.out.println("SecondFilter's doFilter.");

		// pass the request along the filter chain
		chain.doFilter(request, response);
	}

	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}

}

ThirdFilter.java

package com.servlet;

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 ThirdFilter implements Filter {

	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		System.out.println("ThirdFilter's doFilter.");

		// pass the request along the filter chain
		chain.doFilter(request, response);
	}

	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}

}

3.web.xml参照如下

<?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>PrcServlet_0500_Filter</display-name>
  
  <filter>
    <filter-name>SecondFilter</filter-name>
    <filter-class>com.servlet.SecondFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>SecondFilter</filter-name>
    <url-pattern>/URLServlet</url-pattern>
  </filter-mapping>
  
  <servlet>
    <servlet-name>FirstServlet</servlet-name>
    <servlet-class>com.servlet.FirstServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>FirstServlet</servlet-name>
    <url-pattern>/URLServlet</url-pattern>
  </servlet-mapping>
  
  <filter>
    <filter-name>ThirdFilter</filter-name>
    <filter-class>com.servlet.ThirdFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>ThirdFilter</filter-name>
    <url-pattern>/URLServlet</url-pattern>
  </filter-mapping>
  
</web-app>

url-pattern都是/URLServlet。

4.运行结果如下：

SecondFilter's doFilter.
ThirdFilter's doFilter.
FirstServlet's doGet.

在Servlet处理请求之前，与此Servlet关联的Filter首先执行，然后才执行Servlet。

如果一个Servlet有多个Filter，在web.xml文件中，靠前的Filter先执行。