如何并行运行Java for循环？

Question

I am newbie learning selenium and wrote below java code. I am trying to run a for loop that is supposed to load the site 20 times. Right now it does loop in sequential order and I want that to be run in parallel. Can you please help.

public class lenders {

   //ExtentReports logger = ExtentReports.get(lenders.class);
   public static void main(String[] args) throws InterruptedException  {

   for (int i=0; i<20; i++) {
      FirefoxDriver driver= new FirefoxDriver();
      driver.manage().timeouts().pageLoadTimeout(1, TimeUnit.SECONDS);

      try {
         driver.get("https://www.google.com");
      } catch (TimeoutException e) {
           driver.quit();
      }
}

Towards the end I want 20 browsers to be open and loading the site and all of them getting killed.

Answer 1

If you are on Java-8 you can run a parallel for loop using a parallelStream

 IntStream.range(0,20).parallel().forEach(i->{
         ... do something here
 });

Answer 2

In general and at a high level, trying to run code in parallel within java means that you are trying to run multi-threaded code (more than one thread executing at one time).

As individuals have been saying in comments, one must therefore give a warning with my answer. Multi-threading in itself is a complicated topic and one must enter this territory with caution as there can be many issues/topics regarding "thread safety" and even if this is the way you "should" approach the "business request".

In any case, if you really want to create something multi-threaded then I would direct you to a few technical items to get you STARTED on the topic training (and your own further research): You could create another class that implements the Callable interface. It will then have to have the "call" method by nature of implementing that interface. In this class and in the "call" method you would put the actual logic that you want to happen in parallel. In your case, all of the driver, etc.

Then in your parent class (the one you put code from above), you can use a FixedThreadPool and an associated ExecutorService that accepts this callable class. It will essentially run the "call" method in a separate thread so that your for loop can continue onwards at the same time that the logic in the "call" method is executed. It will go the second time around and create another thread, etc. You can manage how many threads are created using your thread pool. You can use different kind of thread pools and services, etc. Again, this is a really BIG topic and field. I am just trying to get your nose in a direction for you to start researching it further.

People might not like my answer because they think you should use completely different technologies other than using Selenium in this manner, etc. I totally understand that point of view and don't disagree with those alternate answers. However, your question was "how to get this running at the same time" and I have tried to give you the building block answer. I hope that helps! Let me know if you need some links to tutorials or anything, but google "ExecutorService" "Thread Pool" and "Callable" (or combinations of them) with the word java and tutorial should get you a variety of answers on the topic.

I hope that helps!