Using threads and collecting responses

Question

Hello,
I am doing multiple requests to diferent web services from diferent providers. I want to do the requests simultaneously and I think the best way is using threads. I am thinking to create a main class that creates a thread instance for every request (max 5) and then wait for the responses with a timeout. What is best way to implement this? Is there any standard or typical strategy? Different points to consider are:
- time out, the main class can't wait for ever the threads to end.
- how every thread passes the response from de web service to the main class.
Thanks in advance.

Answer 1

Hi,
best way to do this may be using an executor service. I cant describe this in detail here..basicly you have to create a executor
ExecutorService executor = Executors.newCachedThreadPool();then you create so called "Callables" which are like Runnables, but return a result. There you implement your thread functionality in the "call" method.
public class testCallable implements Callable{
          public Object call() throws Exception {
}in your controlling class you add these to your executor service and assign the results to a Future (which is a nonblocking operation).
    // make a new Thread for each resouce
          Future[] futures = new Future[5];
          for (int i = 0; i < 5; i++) {
               futures[i] = executor.submit(new testCallable());
          }then you retrive the result. You can assign a timeout there.
try {
             long timeoutTime = System.currentTimeMillis() + timeout;
          for (int i = 0; i < futures.length; i++) {
               long remainingTime = Math.max(0, timeoutTime
                         - System.currentTimeMillis());
               try {
                    Result result = (Result) futures.get(
                              remainingTime, TimeUnit.MILLISECONDS);
look at
http://java.sun.com/javase/6/docs/api/java/util/concurrent/ExecutorService.html
for details
Greetings
Brash