java - how can I count the number of exception thrown by threads? -

i have code:

@test public void setusernamepropertyfrommultithreadsupdatescorrectly() throws exception {     boolean oldval = usersconfig.s.no_db_mode;         final list<string> lastname = new arraylist<string>();         usersconfig.s.no_db_mode = true;          string user1 = testutils.generateusername();         final long createdid = testutils.createuserwithproperties(immutablemap.of("username", user1, "a", "a1",                 "isstaff", "true"));          list<callable<void>> callables = new arraylist<callable<void>>();         (int = 0; < 20; i++) {             callables.add(new callable<void>() {                 @override                 public void call() throws exception {                     string user2 = testutils.generateusername();                     boolean issuccess = usersserveraccess.setproperties(createdid,                             immutablemap.of("isstaff", "dont_know", "username", user2),                             1, "test set", sometimeout);                     asserttrue(issuccess);                      synchronized (lastname) {                         lastname.add(user2);                     }                     return null;                 }             });          executorservice executorservice = executors.newfixedthreadpool(10);         try {             executorservice.invokeall(callables);             executorservice.shutdown();             executorservice.awaittermination(1, timeunit.minutes);         } catch (interruptedexception e) {             e.printstacktrace();             throw new runtimeexception(e);         }          user returneduser = usersserveraccess.getuser(createdid, "get test", sometimeout);         assertthat(returneduser.getproperty("username"), equalto(lastname.get(0)));         assertthat(returneduser.getproperty("a"), equalto("a1"));         assertthat(returneduser.getproperty("isstaff"), equalto("dont_know")); } 

i want assert none of threads threw exception.

how can this?

i can save aside future list. what?

when execute get() on future might executionexception, use getcause() return actual exception.