关于 Cannot forward after response has been committed的错误

 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     @Override12     public void init(FilterConfig filterConfig) throws ServletException {13 14     }15 16     @Override17     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               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     @Override31     public void destroy() {32 33     }34 }

  if (returnValue != null) {      request.getRequestDispatcher("/" + returnValue.toString()).forward(request, response);  }