Question

I have a Java EE web application. Now when a particular request comes (say /xyz url patter) I want to do complex procesing as follows

Each of the following 3 steps are very complex and takes time.

1. Get data from one table from DB.Table has huge data and querying takes time.
2. Make a web service call to some other webserive A and get its data.
3. Make another web service call to some otheer webserice B and get its data .
4. Do some processing by using output of 1, 2, 3

1, 2, and 3 are independent of each other so can be called in parallel.

Now the questions are:

1. Can I do operations 1, 2, and 3 in three separate threads?
2. Is it advisable to create 3 threads for each request?
3. Should I use thread pooling?

Answer 1

To address your first question I go through the 4 steps:

1. Yes, if the database driver you are using allows concurrent access, respectively is safe to use from different threads.
2. A web service is normally designed to deal with different requests at the same time so this should work as well, the question here is how many threads you want to use (and how long it takes to process one request) and whether the web service will guard itself against too many requests at once.
3. The same applies here.
4. Yes, but you have to do synchronization here, as in: wait until all threads have received their results. You can realize this with a java.util.concurrent.CyclicBarrier

Second question
That depends on your data and especially how fast the web services will answer, you should try it out.

Third question Definitively, that’s what they are for. This will also help you to structure your application.