Servlet 发生异常： Cannot call sendRedirect() after the response has been committed!

运行时发生异常：

Cannot call sendRedirect() after the response has been committed

代码：

if(userid==null||userid.trim().length()==0){response.sendRedirect("register.jsp");}if(password==null||password.trim().length()==0){response.sendRedirect("register.jsp");}

如果都进入这些if里面了  都会执行response.sendRedirect("register.jsp");
而response.sendRedirect只能执行一次！

解决：

response.sendRedirect（） 后面加入return!