Cannot forward after response has been committed

在servlet中调用：RequestDispatcher rd = request.getRequestDispatcher(“/welcome.jsp”);
rd.forward(request , response);
转发请求时，出现一下异常：
Cannot forward after response has been committed.

暂时解决办法：

使用匿名调用（request.getRequestDispatcher(“/welcome.jsp”).forward(request , response);）问题解决，也不知道为啥？