Suggestion : Making parallel call from my service to another micro service

Question

I have a requirement as follows

• Make a DB call based on certain criteria and fetch list of result
• For each record present in list, make a GET api call to a microservice
• Consolidate all result from micro-service and give response

I want to make the second step parallel. Now I know based on data that no more than 15 records will be present in list. So I thought of using executorservice for this.

Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors())

Now I am not very confident as to whether

1. Is using ExecutorService the best approach for my scenario. Or I should be using something else
2. Should I create a new executor like Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors()) or let container inject a managed Executor using @Autowired

Answer 1

Since you have a List of records, you may iterate through it using parallelStream .

List<SomeObject> objectList = resultFromDB();
objectList.parallelStream()
          .map(obj -> makeApiCallInParallel(obj))
          .collect(Collectors.toList());

parallelStream will perform API calls in parallel. The number of parallel calls is limited by the number of threads of your CPU.

You may increase it using JVM property:

-Djava.util.concurrent.ForkJoinPool.common.parallelism=20