getWriter() has already been called for this response

问题描述：
servlet中先调用PrintWriter out = response.getWriter();我使用jfreechart的时候需要用到ServletOutputStream outputStream = response.getOutputStream();此时报错如下：

getWriter() has already been called for this response

意思是response已经被其他对象调用了，导致无法继续使用如下类似的方法：

out.print();
out.flush();
out.close();

解决方案：

response.reset();//重点
response.setHeader("Cache-Control", "no-cache");
response.setContentType("image/png");
ServletOutputStream outputStream = response.getOutputStream();