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    <p>There are a few items to discuss, each with their own (part of a) solution:</p> <ul> <li>Do you really want the task to continue if the browser closes? Spawn a new thread for the task (Trying to write to the browser outputstream when browser is already closed will make the thread die in an exception) See <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executor.html" rel="nofollow noreferrer">Executor</a></li> <li>Do you want concurrent requests to be handled in parallel? How many in parallel? See <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ThreadPoolExecutor.html" rel="nofollow noreferrer">ThreadPoolExecutor</a></li> <li>Do you want feedback to the browser (user) during the long running task? See <a href="http://docs.oracle.com/javaee/6/api/javax/servlet/AsyncContext.html" rel="nofollow noreferrer">Async servlets</a></li> </ul> <p>The servlet container will make sure that parallel requests are handled concurrently, each in their own thread. But they will share the instance of the Servlet class. Therefore, you have to make your code <a href="https://stackoverflow.com/a/6324145/637423">thread</a> <a href="https://stackoverflow.com/a/9557412/637423">safe</a>.</p> <p>About running a 'separate java program' or keeping the task in the servlet: it is best practice to separate different tasks in a program in different sections. Creating a new class for your long running task is better than keeping it in the servlet class. See <a href="http://en.wikipedia.org/wiki/Separation_of_concerns" rel="nofollow noreferrer">Separation of concerns</a>.</p>
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    1. COThe results aren't going to be displayed on the browser. They'll be mailed to the user, so that's of no issue here. My main concerns are if the servlet will run the task for each user request _independent of each other_ automatically or should I do that **and** should I dedicate a separate Java program for the task or can it be contained in the servlet class itself?
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    2. CO@vigneshwerv I added thread safety and separation of concerns to the answer
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    3. COThank you @Geert.
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