错误 getWriter() has already been called for this response 的解决方法

HttpServletResponse在调用getWriter和getOutputStream两者之间之间只能选择一个，但有时已经调用过getOutputStream，仍然想调用getWriter，不难，用 java io 类嵌套一下就可以：

1     OutputStream out = null;
2     OutputStreamWriter ow = null; 
3    
4     out = resp.getOutputStream();
5     ow = new OutputStreamWriter(out);
6     ow.append("你想要添加的东西");