这个错误顾名思义:就是在给客户端做出提交响应完毕后,就不能再次使用request的转发。
代码原先是这样的:
1 package com.bdqn.jsp.study.web.filter; 2 3 import javax.servlet.*; 4 import javax.servlet.annotation.WebFilter; 5 import javax.servlet.http.HttpServletRequest; 6 import javax.servlet.http.HttpServletResponse; 7 import java.io.IOException; 8 9 @WebFilter(filterName = "checkLoginFilter", urlPatterns = "/*") 10 public class CheckLoginFilter implements Filter { 11 @Override 12 public void init(FilterConfig filterConfig) throws ServletException { 13 14 } 15 16 @Override 17 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { 18 HttpServletRequest request = (HttpServletRequest) servletRequest; 19 HttpServletResponse response = (HttpServletResponse) servletResponse; 20 if (request.getRequestURI().contains("/user")) { 21 Object value = request.getSession().getAttribute("user"); 22 if (value == null) { 23 response.sendRedirect(request.getContextPath() + "/login.jsp"); 24 //return; 25 } 26 } 27 filterChain.doFilter(request, response); 28 } 29 30 @Override 31 public void destroy() { 32 33 } 34 }
注意这里是个filter主要作用:用于判断用户是否登录后才能访问相关页面,地址栏里有“/user”的地址信息,就认为改地址是登录后才能进行访问
然而在某一个servlet里有如下相关代码:
if (returnValue != null) { request.getRequestDispatcher("/" + returnValue.toString()).forward(request, response); }
如果这么写就出问题了,因为在filter里response做出重定向后,还要执行doFilter方法,因此当执行servlet中的转发操作时就会报错了,因为在response.sendRedirect()会认为已经给response的commited属性设置成true了,因此不能再进行转发