关闭输出流后，servlet请求会怎样？

Question

We are running on tomcat for our application server.

We have a servlet that generates a PDF and returns it to the browser. It then deletes the temporary PDF file.

The issue is that we were having some timing difficulties with the delete. Someone on our team decided that we should wait 20 seconds before we delete the file, so they use a Thread.sleep(20000).

The interesting thing is that they close the output stream, wait 20 seconds, and then delete the file and exit doGet().

My question is this: Since the output stream is closed on the response, it returns immediately to the browser before the wait, are there any performance concerns to the additional 20 seconds wait? For example, does it tie up a network connection or some such?

Answer 1

Well no, I have put something like that in an application and its running for quite sometime now, only the output stream is closed, so you can't communicate with the user's current request anymore, but since the doGet did not exist so the servlet's object is not destroyed until the thread timeout ends.

There will probably be no issues regarding the network bandwidth, because the deletion and the waiting only happens in memory, like a background task, the only thing that affects that network's bandwidth is the time taken to send a response and since you respond fast, and then finish your work later then its ok.

I would suggest however to use a destroy() method instead to delete the file.

Answer 2

I would suggest using File.createTempFile() to create your temporary file (unless you have already tried this and is not feasible for you for whatever reason) and let Java decide when to delete it. By using Thread.sleep() in your servlet you are essentially holding the servlet instance. The ServletContainers create a pool of servlets for subsequent requests and any servlet living for 20 seconds will increase your pool size and the Servlet will not be available for the next request hence the container will have no option other than to create a new instance for subsequent requests.

There may not be any network or bandwidth related issues. However, holding on to a Servlet in the way you are describing is a recipe for disaster.