Spring Boot executing parallel methods inside a controller

Question

I'm trying to execute some parallel methods inside my controller but i'm having a few problems with the return type.

I have 4 methods and each of those methods return a list.I need to execute those methods in a parallel way and then get each returned list and place all of those lists inside a map and return that map from the controller. Here's the code:

Callable<List> callable1 = new Callable<List>()
           {
              @Override
              public List call() throws Exception
              {
                List<SearchResultAutovit> lista;
                lista = scrapperAutovit.searchAutovit(marcaId, modelId, pretDeLa, pretPanaLa, anFabrDeLa, anFabrPanaLa,
                        orasParam);
                 return lista;
              }
           };

           Callable<List> callable2 = new Callable<List>()
           {
              @Override
              public List call() throws Exception
              {
                  List<SearchResultOlx> listaOlx;
                String marcaOlx = marcaId.toLowerCase();
                String modelOlx = modelId.toLowerCase();
                String orasOlx = orasParam.toLowerCase();
                listaOlx = scrapperOlx.searchOlx(marcaOlx, modelOlx, pretDeLa, pretPanaLa, anFabrDeLa, anFabrPanaLa, orasOlx);
                 return listaOlx;
              }
           };

           Callable<List> callable3 = new Callable<List>()
           {
              @Override
              public List call() throws Exception
              {
                List<SearchResultPubli24> listaPubli24;
                String orasPubli24 = orasParam.toLowerCase();
                listaPubli24 = scrapperPubli24.searchPubli24(marcaId, modelId, orasPubli24, anFabrDeLa, anFabrPanaLa, pretDeLa, pretPanaLa);
                 return listaPubli24;
              }
           };

           Callable<List> callable4 = new Callable<List>()
           {
              @Override
              public List call() throws Exception
              {
                 List<SearchResultAutoUncle> listaAutoUncle;
                listaAutoUncle = scrapperAutoUncle.searchAutoUncle(marcaId, modelId, pretDeLa, pretPanaLa, anFabrDeLa, anFabrPanaLa, orasParam);
                 return listaAutoUncle;
              }
           };

           //add to a list
           List<Callable<List>> taskList = new ArrayList<Callable<List>>();
           taskList.add(callable1);
           taskList.add(callable2);
           taskList.add(callable3);
           taskList.add(callable4);

           ExecutorService executor = Executors.newFixedThreadPool(3);
           executor.invokeAll(taskList);

           Map<String,List<?>> listOfWebsites = new HashMap<>();
            listOfWebsites.put("listaAutovit", (List<?>) taskList.get(0));
            listOfWebsites.put("listaOlx", (List<?>) taskList.get(1));
            listOfWebsites.put("listaPubli24", (List<?>) taskList.get(2));
            listOfWebsites.put("listaAutoUncle", (List<?>) taskList.get(3));

        return listOfWebsites;

I'm pretty sure that i'm not doing something right because it throws java.lang.ClassCastException: com.test.controller.HomeController$1 incompatible with java.util.List I guess the problem is the map called listOfWebsites which should have the returned type of the callables, some lists:(

Sorry, misread the question. I'm in a noisy room. I'll remove my comment. — duffymo
– duffymo, Commented Nov 18, 2018 at 14:10
Hint HomeController$1 is your Callable... More generally though, you should plan to do the whole process asynchronously and return a Future from your controller method. — Boris the Spider
– Boris the Spider, Commented Nov 18, 2018 at 14:10

Alexei Kaigorodov · Accepted Answer · 2018-11-18 16:23:31Z

4

First, change type of callables to avoid casting:

    Callable<List<?>> callable1 = new Callable<List>(){...}

Then, you have to wait for results of parallel computations. You need not to create CompletableFutures because you can obtain Futures directly from ExecutorService:

    ExecutorService executor = Executors.newFixedThreadPool(3);
    Future<List<?>> future1 = executor.submit(callable1);
    Future<List<?>> future2 = executor.submit(callable2);
    Future<List<?>> future3 = executor.submit(callable3);
    Future<List<?>> future4 = executor.submit(callable4);

    Map<String,List<?>> listOfWebsites = new HashMap<>();
    listOfWebsites.put("listaAutovit", future1.get());
    listOfWebsites.put("listaOlx", future2.get());
    listOfWebsites.put("listaPubli24", future3.get());
    listOfWebsites.put("listaAutoUncle", future4.get());

    return listOfWebsites;

That's it.

edited Nov 18, 2018 at 16:23

answered Nov 18, 2018 at 14:58

Alexei Kaigorodov

13.6k1 gold badge24 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

GauravRai1512 · Accepted Answer · 2018-11-18 14:20:37Z

1

I would suggest to use completableFuture Object with supplyasync method. Giving you approach like below:

CompletableFuture<String> completableFuture
  = CompletableFuture.supplyAsync(() -> scrapperAutovit.searchAutovit);

CompletableFuture<String> completableFuture1
  = CompletableFuture.supplyAsync(() -> scrapperOlx.searchOlxwith);

CompletableFuture<String> completableFuture2
  = CompletableFuture.supplyAsync(() -> scrapperPubli24.searchPubli24);

would be used to check whether you got some response from above call or not.

Like that you can open parallel thread for scrapperOlx.searchOlxwith and scrapperPubli24.searchPubli24 completableFuture object and wait for execution to finish there task and after that consolidate all data and you can process further.

For more details you can refer below link https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html https://dzone.com/articles/java-8-definitive-guide https://www.callicoder.com/java-8-completablefuture-tutorial/

This is the good example to understand completablefuture Multiple thenApply in a completableFuture

edited Nov 18, 2018 at 14:20

answered Nov 18, 2018 at 14:00

GauravRai1512

8446 silver badges14 bronze badges

4 Comments

Truica Sorin Over a year ago

I'm not sure i understand:( where should i use this CompletableFuture?

GauravRai1512 Over a year ago

all future object which you have created in callable can use by completablefuture like i have mentioned one example for scrapperAutovit.searchAutovit like you can parallel y run with scrapperOlx.searchOlx this as so on i have also shared few link you just go through this link you will understand its a java8 future object.

Boris the Spider Over a year ago

Note this will use the common pool rather than a custom executor.

GauravRai1512 Over a year ago

You can provide the custom executor as well through constructor.public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor) { return asyncSupplyStage(screenExecutor(executor), supplier); }

Collectives™ on Stack Overflow

Spring Boot executing parallel methods inside a controller

2 Answers 2

Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related