java.lang.IllegalStateException: PWC3990: getWriter() has already been called for this response
How to solve this error? I run a simple servlet code to display the bar graph.
You cannot call both getOutputStream() and getWriter() on the same response. Keep in mind that JSP implicitly uses getWriter().
An Illusion
Also make sure that the request is not being redirected to current servlet from some place else. If it is, then there is a high probability that one of getOutputStream() or getWriter() has already been called on it.
来源：https://stackoverflow.com/questions/4312309/illegalstateexception-pwc3990-getwriter-has-already-been-called-for-this-res