IllegalStateException: PWC3990: getWriter() has already been called for this response

问题

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.

回答1:

You cannot call both getOutputStream() and getWriter() on the same response. Keep in mind that JSP implicitly uses getWriter().

回答2:

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