Threading in Servlets

I am working on a servlet that can take a few hours to complete the request. However, the client calling the servlet is only interested in knowing whether the request has been received by the servlet or not. The client doesn't want to wait hours before it gets any kind of response from the servlet. Also since calling the servlet is a blocking call, the client cannot proceed until it receives the response from the servlet. To avoi开发者_C百科d this, I am thinking of actually launching a new thread in the servlet code. The thread launched by the servlet will do the time consuming processing allowing the servlet to return a response to the client very quickly. But I am not sure if this an acceptable way of working around the blocking nature of servlet calls. I have looked into NIO but it seems like it is not something that is guaranteed to work in any servlet container as the servlet container has be NIO based also.

What you need is a job scheduler because they give assurance that a job will be finished, even in case a server is restarted.

Take a look at java OSS job schedulers, most notably Quartz.

Your solution is correct, but creating threads in enterprise applications is considered a bad practice. Better use a thread pool or JMS queue.

You have to take into account what should happen server goes down during processing, how to react when multiple requests (think: hundreds or even thousands) occur at the same time, etc. So you have chosen the right direction, but it is a bit more complicated.

A thread isn't bad but I recommend throwing this off to an executor pool as a task. Better yet a long running work manager. It's not a bad practice to return quickly like you plan. I would recommend providing some sort of user feedback indicating where the user can find information about the long running job. So:

1. Create a job representing the work task with a unique ID
2. Send the job to your background handler object (that contains an executor)
3. Build a url for the unique job id.
4. Return a page describing where they can get the result

The page with the result will have to coordinate with this background job manager. While it's computing you can have this page describe the progress. When its done the page can display the results of the long running job.