The file can be downloaded, but the error is: Java. Lang. illegalstateexception: getoutputstream () has already been called for this respon.

During download, the file can be correctly downloaded, but an error is always reported.

Java. Lang. illegalstateexception: getoutputstream () has already been called for this response

Solution:
Outside the scope of java scripts (that is, outside the scope of <%... %>), do not include HTMLCodeCharacters such as space, carriage return, or line feed cannot be correctly downloaded if any. If you do not believe it, you can add a line break between %> <% in the source code and download it again to ensure that an error occurs. It affects the data streams returned to the browser, resulting in parsing errors.
Solve the problem after modification.