Cannot forward after response has been committed 问题原因。
2016-08-29 20:04
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一般这种情况下,是因为在程序运行过程中”同时“发送了两次请求转发。
个人这样理解的:在程序遇到请求转发后并没有立即执行,代码还是会继续往下面走,最后才会去转发。下面是我的错误代码(只放关键语句)
String type = request.getParameter("type"); if("user_update" .equals(type)){ request.getRequestDispatcher("success.jsp").forward(request, response); }else{ request.getRequestDispatcher("error.jsp").forward(request, response); } if("user_delect".equals(type)){ String message = ""; if(number > 0){ message = "删除成功"; request.getRequestDispatcher("success.jsp").forward(request, response); }else{ message = "删除失败"; request.getRequestDispatcher("error.jsp").forward(request, response); } }
根据页面传递参数的不同来确定操作。但是判断type属性的时候,该if语句不应该有else。比如:
如果页面点击“删除”按钮,这时候获取的type值为”user_delect“,但是由于代码执行顺序,它会进入第一个判断时候是”user_update“的else中然后进行转发,之后又进入了下面的if中进行转发,就出现了两次请求转发。
还有一中情况就是,第二个if去掉了else,这样也会导致执行两次请求。
关于其它请求问题,好像有个return null 能解决在返回之前就转发的情况,暂时没有遇到,以后再写出来。
就是如果不使用上述方法,那么就使用return进行手动的结束。
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