I have the following code in which I am using a few methods from rxJava api like buffer, observable from iterable, and parallization. I get inspired by this post: RxJava and parallel execution of observer code
and I am almost sure I did it as https://stackoverflow.com/users/1011435/lordraydenmk has explained in his post, but my code is still executed sequentially in main thread;/ anybody can help me figure out what I am doing wrong here?
Thanks in advance!
private static Observable<String> getPositions(List<String> id) throws InterruptedException {
System.out.println("thread: " + Thread.currentThread().getName());
Thread.sleep(500);
return Single.fromCallable(() -> {
if (id.contains("3")) {
return Arrays.asList("a", "aa", "aaa");
} else if (id.contains("2")) {
return Arrays.asList("b", "bb", "bbb");
}
return Arrays.asList("c", "cc", "ccc");
}).flatMapObservable(Observable::fromIterable).subscribeOn(Schedulers.computation());
}
public static void main(String[] args) throws InterruptedException {
Observable<String> a = Observable.fromIterable(Arrays.asList("1", "2", "3"));
a.buffer(2).flatMap(buff -> getPositions(buff), 4).toList().subscribe(val -> System.out.println(val));
Thread.sleep(1500);
}
the output is:
thread: main
thread: main
[b, bb, bbb, a, aa, aaa]
Related
When writing tests around code that will throw an exception, how can Dart/Mockito(or anything else) avoid throwing a real exception?
For example, these tests should both pass and detect the thrown exception - but Dart throws a real exception in the 1st test so only 'It receives a Todo' passes.
void main() {
test('It throws an exception', () async {
final client = MockClient();
when(client.get(Uri.parse('https://jsonplaceholder.typicode.com/todos/1'))).thenAnswer((_) async => http.Response('', 404));
expect(await fetchTodo(client, 1), throwsException);
});
test('It receives a Todo', () async {
final client = MockClient();
final jsonString = '''
{
"id": 1,
"userId": 1,
"title": "test",
"completed": false
}
''';
when(client.get(Uri.parse('https://jsonplaceholder.typicode.com/todos/2'))).thenAnswer((_) async => http.Response(jsonString, 200));
expect(await fetchTodo(client, 2), isA<Todo>());
});
}
and the mocked get method(based on mockito's generated code - I get the same results when using #GenerateMocks([http.Client]) in my test file.
class MockClient extends Mock implements http.Client {
Future<http.Response> get(Uri url, {Map<String, String>? headers}) {
return super.noSuchMethod(Invocation.method(#get, [url], {#headers: headers}), returnValue: Future.value(http.Response('', 200))) as Future<http.Response>;
}
}
class Todo {
int id;
int userId;
String title;
bool completed;
Todo(this.id, this.userId, this.title, this.completed);
}
Future<Todo> fetchTodo(http.Client client, int id) async {
final response = await client.get(Uri.parse('https://jsonplaceholder.typicode.com/todos/$id'));
if(response.statusCode == 200) {
return Todo(1, 1, 'Test', true);
}else {
throw Exception('Failed to fetch resource');
}
}
Test run report:
00:00 +0: It throws an exception
00:00 +0 -1: It throws an exception [E]
Exception: Failed to fetch resource
test/test.dart 49:5 fetchTodo
00:00 +0 -1: It receives a Todo
00:00 +1 -1: Some tests failed.
Your problem is that you do:
expect(await fetchTodo(client, 1), throwsException);
expect() is a normal function, and function arguments are evaluated before the function is invoked. (Dart is an applicative-order language.) You therefore must wait for fetchTodo to complete before calling expect() (and before expect can try to match against the throwsException Matcher).
As explained by the throwsA documentation (and this applies to the throwsException Matcher too), it must be matched against a zero-argument function or a Future. You do not need to (and should not) await the call to fetchTodo.
Also, since you're calling an asynchronous function, the expectation cannot be checked synchronously, so you'll also need to use expectLater instead of expect:
await expectLater(fetchTodo(client, 1), throwsException);
To prevent the XY problem, I'll start from the beginning:
I have a non-blocking SOAP client which I wrapped it to make the return type Mono<T> (By default it accepts callback. I can elaborate on this if needed).
Now I want to do (given ID):
1. Get the code by ID
2. Do something with the code
3. After that, get Foo and Bar and create FooBar
What I wrote was:
public class MyService {
private final MySoapClient soapClient;
public Mono<FooBarDto> doSomething(String id) {
return Mono.just(id)
.flatMap(soapClient::getCode) // returns Mono<String>
.flatMap(code ->
soapClient.doSomething(code) // returns Mono<Void>
.then(getFooBar(id, code))); // See this
}
private Mono<FooBarDto> getFooBar(String id, String code) {
return Mono.zip(
soapClient.getFoo(code), // returns Mono<Foo>
soapClient.getBar(code) // returns Mono<Bar>
).map(tuple2 -> toFooBarDto(id, tuple2));
}
private FooBarDto toFooBarDto(String id, Tuple2<Foo, Bar> tuple2) {
return FooBarDto.builder()/* set properties */.build();
}
}
Now the problem is, because methods of the SOAP client are not lazy (the moment you call them they start the process), the semantic of then won't work here. Meaning I want to get Foo and Bar when doSomething is done. They all start together.
I tried to change it fix it by changing then to flatMap, but made it even worse. The getFooBar never got called. (1. Can someone please explain why?).
So what I ended up doing was to wrap SOAP calls again to make them lazy:
public class MySoapClient {
private final AutoGeneratedSoapClient client;
Mono<Foo> getFoo(GetFooRequest request) {
return Mono.just(request).flatMap(this::doGetMsisdnByIccid);
}
private Mono<Foo> doGetFoo(GetFooRequest request) {
val handler = new AsyncHandler<GetFooRequest>();
client.getFoo(request, handler);
return Mono.fromFuture(handler.future);
}
private static class AsyncHandler<T> implements javax.xml.ws.AsyncHandler<T> {
private final CompletableFuture<T> future = new CompletableFuture<>();
#Override
public void handleResponse(Response<T> res) {
try {
future.complete(res.get());
} catch (Exception e) {
future.completeExceptionally(e);
}
}
}
}
Is there any better way to do it? Specifically:
2. Using CompeletableFuture and the callback.
3. Making methods lazy in the SOAP client.
I tried to change it fix it by changing then to flatMap, but made it
even worse. The getFooBar never got called. (1. Can someone please
explain why?)
I think a Mono<Void> always completes empty (or error), so subsequent flatMap is never called.
Using CompeletableFuture and the callback.
Making methods lazy in the SOAP client.
To make the call lazy you can do one of the followings:
1, You can use Mono.fromFuture which accepts a supplier:
private Mono<Foo> doGetFoo(GetFooRequest request) {
return Mono.fromFuture(() -> {
val handler = new AsyncHandler<GetFooRequest>();
client.getFoo(request, handler);
return handler.future;
});
}
2, You can use Mono.defer:
private Mono<Foo> doGetFoo(GetFooRequest request) {
return Mono.defer(() -> {
val handler = new AsyncHandler<GetFooRequest>();
client.getFoo(request, handler);
return Mono.fromFuture(handler.future);
});
}
3, You can get rid of CompletableFuture and use Mono.create instead, something like this:
private Mono<Foo> doGetFoo(GetFooRequest request) {
return Mono.create(sink -> {
AsyncHandler<Foo> handler = response ->
{
try
{
sink.success(response.get());
} catch (Exception e)
{
sink.error(e);
}
};
client.getFoo(request, handler);
});
}
If you do any of these it will be safe to use then method and it will work as expected.
I was trying reactor library and I'm not able to figure out why below mono never return back with onNext or onComplete call. I think I missing very trivial thing. Here's a sample code.
MyServiceService service = new MyServiceService();
service.save("id")
.map(myUserMono -> new MyUser(myUserMono.getName().toUpperCase(), myUserMono.getId().toUpperCase()))
.subscribe(new Subscriber<MyUser>() {
#Override
public void onSubscribe(Subscription s) {
System.out.println("Subscribed!" + Thread.currentThread().getName());
}
#Override
public void onNext(MyUser myUser) {
System.out.println("OnNext on thread " + Thread.currentThread().getName());
}
#Override
public void onError(Throwable t) {
System.out.println("onError!" + Thread.currentThread().getName());
}
#Override
public void onComplete() {
System.out.println("onCompleted!" + Thread.currentThread().getName());
}
});
}
private static class MyServiceService {
private Repository myRepo = new Repository();
public Mono<MyUser> save(String userId) {
return myRepo.save(userId);
}
}
private static class Repository {
public Mono<MyUser> save(String userId) {
return Mono.create(myUserMonoSink -> {
Future<MyUser> submit = exe.submit(() -> this.blockingMethod(userId));
ListenableFuture<MyUser> myUserListenableFuture = JdkFutureAdapters.listenInPoolThread(submit);
Futures.addCallback(myUserListenableFuture, new FutureCallback<MyUser>() {
#Override
public void onSuccess(MyUser result) {
myUserMonoSink.success(result);
}
#Override
public void onFailure(Throwable t) {
myUserMonoSink.error(t);
}
});
});
}
private MyUser blockingMethod(String userId) throws InterruptedException {
Thread.sleep(5000);
return new MyUser("blocking", userId);
}
}
Above code only prints Subcribed!main. What I'm not able to figure out is why that future callback is not pushing values through myUserMonoSink.success
The important thing to keep in mind is that a Flux or Mono is asynchronous, most of the time.
Once you subscribe, the asynchronous processing of saving the user starts in the executor, but execution continues in your main code after .subscribe(...).
So the main thread exits, terminating your test before anything was pushed to the Mono.
[sidebar]: when is it ever synchronous?
When the source of data is a Flux/Mono synchronous factory method. BUT with the added pre-requisite that the rest of the chain of operators doesn't switch execution context. That could happen either explicitly (you use a publishOn or subscribeOn operator) or implicitly (some operators like time-related ones, eg. delayElements, run on a separate Scheduler).
Simply put, your source is ran in the ExecutorService thread of exe, so the Mono is indeed asynchronous. Your snippet on the other hand is ran on main.
How to fix the issue
To observe the correct behavior of Mono in an experiment (as opposed to fully async code in production), several possibilities are available:
keep subscribe with system.out.printlns, but add a new CountDownLatch(1) that is .countDown() inside onComplete and onError. await on the countdown latch after the subscribe.
use .log().block() instead of .subscribe(...). You lose the customization of what to do on each event, but log() will print those out for you (provided you have a logging framework configured). block() will revert to blocking mode and do pretty much what I suggested with the CountDownLatch above. It returns the value once available or throws an Exception in case of error.
instead of log() you can customize logging or other side effects using .doOnXXX(...) methods (there's one for pretty much every type of event + combinations of events, eg. doOnSubscribe, doOnNext...)
If you're doing a unit test, use StepVerifier from the reactor-tests project. It will subscribe to the flux/mono and wait for events when you call .verify(). See the reference guide chapter on testing (and the rest of the reference guide in general).
Issue is that in created anonymous class onSubscribe method does nothing.
If you look at implementation of LambdaSubscriber, it requests some number of events.
Also it's easier to extend BaseSubscriber as it has some predefined logic.
So your subscriber implementation would be:
MyServiceService service = new MyServiceService();
service.save("id")
.map(myUserMono -> new MyUser(myUserMono.getName().toUpperCase(), myUserMono.getId().toUpperCase()))
.subscribe(new BaseSubscriber<MyUser>() {
#Override
protected void hookOnSubscribe(Subscription subscription) {
System.out.println("Subscribed!" + Thread.currentThread().getName());
request(1); // or requestUnbounded();
}
#Override
protected void hookOnNext(MyUser myUser) {
System.out.println("OnNext on thread " + Thread.currentThread().getName());
// request(1); // if wasn't called requestUnbounded() 2
}
#Override
protected void hookOnComplete() {
System.out.println("onCompleted!" + Thread.currentThread().getName());
}
#Override
protected void hookOnError(Throwable throwable) {
System.out.println("onError!" + Thread.currentThread().getName());
}
});
Maybe it's not the best implementation, I'm new to reactor too.
Simon's answer has pretty good explanation about testing asynchronous code.
I'm new to reactive programming using rxjava and after going through the simpler examples I'm now trying to figure out how to work with continuous streams. The problem I have with the example below is that the program doesn't terminate after I've taken the 3 elements. My assumption is that I somehow need to unsubscribe to my observable but I don't fully grasp how to terminate the while loop and make the program exit.
I've come across the following post RxJava -- Terminating Infinite Streams but I still can't figure out what I'm missing.
class MyTwitterDataProvider {
/*
This example is written in Groovy
Instance variables and constructor omitted
*/
public Observable<String> getTweets() {
BufferedReader reader = new BufferedReader(new InputStreamReader(getTwitterStream()))
Observable.create({ observer ->
executor.execute(new Runnable() {
def void run() {
String newLine
while ((newLine = reader.readLine()) != null) {
System.out.println("printing tweet: $newLine")
observer.onNext(newLine)
}
observer.onCompleted()
}
})
})
}
def InputStream getTwitterStream() {
// code omitted
}
public static void main (String [] args) {
MyTwitterDataProvider provider = new MyTwitterDataProvider()
Observable<String> myTweetsObservable = provider.getTweets().take(3)
Subscription myTweetSubscription = myTweetsObservable.subscribe({tweet-> println("client prints: $tweet")})
// myTweetSubscription.unsubscribe()
}
}
You must add a check in your loop to see if the observer is still subscribed:
while ((newLine = reader.readLine()) != null && !observer.isUnsubsribed()) {
System.out.println("printing tweet: $newLine")
observer.onNext(newLine)
}
I have a JavaFX application which instantiates several Task objects.
Currently, my implementation (see below) calls the behavior runFactory() which performs computation under a Task object. Parallel to this, nextFunction() is invoked. Is there a way to have nextFunction() "wait" until the prior Task is complete?
I understand thread.join() waits until the running thread is complete, but with GUIs, there are additional layers of complexity due to the event dispatch thread.
As a matter of fact, adding thread.join() to the end of the code-segment below only ceases UI interaction.
If there are any suggestions how to make nextFunction wait until its prior function, runFactory is complete, I'd be very appreciative.
Thanks,
// High-level class to run the Knuth-Morris-Pratt algorithm.
public class AlignmentFactory {
public void perform() {
KnuthMorrisPrattFactory factory = new KnuthMorrisPrattFactory();
factory.runFactory(); // nextFunction invoked w/out runFactory finishing.
// Code to run once runFactory() is complete.
nextFunction() // also invokes a Task.
...
}
}
// Implementation of Knuth-Morris-Pratt given a list of words and a sub-string.
public class KnuthMorrisPratt {
public void runFactory() throws InterruptedException {
Thread thread = null;
Task<Void> task = new Task<Void>() {
#Override public Void call() throws InterruptedException {
for (InputSequence seq: getSequences) {
KnuthMorrisPratt kmp = new KnuthMorrisPratt(seq, substring);
kmp.align();
}
return null;
}
};
thread = new Thread(task);
thread.setDaemon(true);
thread.start();
}
When using Tasks you need to use setOnSucceeded and possibly setOnFailed to create a logic flow in your program, I propose that you also make runFactory() return the task rather than running it:
// Implementation of Knuth-Morris-Pratt given a list of words and a sub-string.
public class KnuthMorrisPratt {
public Task<Void> runFactory() throws InterruptedException {
return new Task<Void>() {
#Override public Void call() throws InterruptedException {
for (InputSequence seq: getSequences) {
KnuthMorrisPratt kmp = new KnuthMorrisPratt(seq, substring);
kmp.align();
}
return null;
}
};
}
// High-level class to run the Knuth-Morris-Pratt algorithm.
public class AlignmentFactory {
public void perform() {
KnuthMorrisPrattFactory factory = new KnuthMorrisPrattFactory();
Task<Void> runFactoryTask = factory.runFactory();
runFactoryTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent t)
{
// Code to run once runFactory() is completed **successfully**
nextFunction() // also invokes a Task.
}
});
runFactoryTask.setOnFailed(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent t)
{
// Code to run once runFactory() **fails**
}
});
new Thread(runFactoryTask).start();
}
}