过滤链的一点问题
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | package 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 FilterC implements Filter { @Override public void destroy() { // TODO Auto-generated method stub } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub try { Thread.sleep(3000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } chain.doFilter(request, response); try { Thread.sleep(3000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("I am " + this.getClass().getSimpleName()); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | package 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 FilterB implements Filter { @Override public void destroy() { // TODO Auto-generated method stub } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub chain.doFilter(request, response); System.out.println("I am " + this.getClass().getSimpleName()); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | package 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 FilterA implements Filter { @Override public void destroy() { // TODO Auto-generated method stub } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub chain.doFilter(request, response); System.out.println("I am " + this.getClass().getSimpleName()); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | <?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>filter-chain</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> <welcome-file>default.html</welcome-file> <welcome-file>default.htm</welcome-file> <welcome-file>default.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>A</filter-name> <filter-class>filter.FilterA</filter-class> </filter> <filter> <filter-name>B</filter-name> <filter-class>filter.FilterB</filter-class> </filter> <filter> <filter-name>C</filter-name> <filter-class>filter.FilterC</filter-class> </filter> <filter-mapping> <filter-name>A</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter-mapping> <filter-name>B</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter-mapping> <filter-name>C</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app> |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | package filter;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 HelloServlet */@WebServlet("/hello")public class HelloServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public HelloServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().println("hello world"); System.out.println("hello world"); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doGet(request, response); }} |
只有第一个class里面我在chain.dofilter方法前后各加了休眠，其他的都和老师在2-8里面的代码一样，
问下我这段代码访问servlet以后再控制台会打印出
hello world
I am FilterC
I am FilterB
I am FilterA
不是太能理解，当代码回传到filterC的时候，通过chain.dofilter不是已经像前传递了，同时我在它下面设置了休眠，为什么系统不先打印filterb 和 filtera呢？
我以为会是：
hello world,
I am FilterB
I am FilterA
I am FilterC
这个顺序的。
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同学你好，chain.doFilter(request, response);请求转发给过滤器链上下一个对象。这里的下一个指的是下一个filter，如果没有filter就执行请求的资源。
所以执行FilterC中的chain.doFilter(request, response);后没有下一个过滤器，则执行请求/hello，执行完HelloServlet，按过滤器链的逆向顺序执行代码，输出FilterC，FilterB，FilterA。
执行chain.doFilter(request, response);并不是将请求传回前面的过滤器，而是传递给后边的过滤器，如果后边没有过滤器，则执行请求。执行请求后，按过滤器逆向顺序执行过滤器链。
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