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：

    OutputStream out = null;
    OutputStreamWriter ow = null; 
   
    out = resp.getOutputStream();
    ow = new OutputStreamWriter(out);
    ow.append("你想要添加的东西");