How to return Respone from Jersey REST api method which has listners inside

I am trying to create REST apis to perform write operations using [Firebase Server SDK][1] and Jersey.

Here is what I am trying to do:

1. [Initializing Firebase SDK][2]
2. [Getting idToken from Client and Validating idToken][3]
3. Performing some write operations on few Firebase nodes
4. Sending api Response

I want to return Response only if Firebase write operation succeeds or fails.
That happens inside of Firebase Listeners. However, I try to return value from Listeners, I get error becuase Firebase listeners have void return type.

How can I return response from the listener?

Here is my code.

**MyEndpoint.java**




@Path("/restapi")
//BaseEndpoint does Authentication operations
public class MyEndpoint extends BaseEndpoint {

public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
super.Authenticate(token, authenticationResultListener);
}

@POST
@Produces("application/json")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public Response createCommunity(@FormParam("idToken") String idToken) {
Authenticate(idToken, new AuthenticationListener() {
@Override
public void onAuthenticationSuccess() {
// The app only has access as defined in the Security Rules
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("/mysamplenode");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
String res = dataSnapshot.getKey();
//I will do some write operations on Firebase here
//If they complete successfuly only then I want to return api response
return Response.status(200).entity().build();
}
@Override
public void onCancelled(DatabaseError arg0) {
System.out.println("DatabaseError-------------" + arg0);
return Response.status(500).entity("DatabaseError").build();
}
});
}
@Override
public void onAuthenticationFailure() {
return Response.status(403).entity("Forbidden").build();
}
});
}
}

**BaseEndpoint.java**

public class BaseEndpoint {

public static String uid;

public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
// idToken comes from the client app
FirebaseAuth.getInstance().verifyIdToken(token).addOnFailureListener(new OnFailureListener() {

@Override
public void onFailure(Exception arg0) {
System.out.println("Uid exp= " + arg0);
authenticationResultListener.onAuthenticationFailure();
}
}).addOnSuccessListener(new OnSuccessListener<FirebaseToken>() {
@Override
public void onSuccess(FirebaseToken decodedToken) {
uid = decodedToken.getUid();
System.out.println("Uid= " + uid);
authenticationResultListener.onAuthenticationSuccess();
}
});
}
}

[1]:

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[2]:

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[3]:

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So I'm guessing the Firebase SDK is asynchronous in nature. In which case, if you're using Jersey 2.x, you can use the [asynchronous server support][1]. You can just call `AsyncResponse.resume(Response)` in your callbacks. For example

@POST
@Produces("application/json")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public void createCommunity(@FormParam("idToken") String idToken,
@Suspended final AsyncResponse response) {
Authenticate(idToken, new AuthenticationListener() {
@Override
public void onAuthenticationSuccess() {
DatabaseReference ref = FirebaseDatabase.getInstance()
.getReference("/mysamplenode");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
String res = dataSnapshot.getKey();
response.resume(Response.status(200).entity().build());
}
@Override
public void onCancelled(DatabaseError arg0) {
response.resume(Response.status(500).entity("DatabaseError").build());
}
});
}
@Override
public void onAuthenticationFailure() {
response.resume(Response.status(403).entity("Forbidden").build());
}
});
}

If you're using Jersey 1.x, there's not really an async option. You just need to block flow with a [`CountDownLatch`][2], assign a local `Response` in the callbacks, and count down.


@POST
@Produces("application/json")
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
public void createCommunity(@FormParam("idToken") String idToken) {
Response response;
CountDownLatch latch = new CountDownLatch(1);
Authenticate(idToken, new AuthenticationListener() {
@Override
public void onAuthenticationSuccess() {
DatabaseReference ref = FirebaseDatabase.getInstance()
.getReference("/mysamplenode");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
String res = dataSnapshot.getKey();
response = Response.status(200).entity().build();
latch.countDown();
}
@Override
public void onCancelled(DatabaseError arg0) {
response = Response.status(500).entity("DatabaseError").build();
latch.countDown();
}
});
}
@Override
public void onAuthenticationFailure() {
response = Response.status(403).entity("Forbidden").build();
latch.countDown();
}
});
latch.await();
return response;
}

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I might be a little late in answering this question, but after trying the Firebase server SDK out I found that you can create a Task available in the SDK to wait for a response synchronously. The snippet below might help you out:

public class BaseEndpoint {

public static String uid;

public void Authenticate(String token, AuthenticationListener authenticationResultListener) {
// idToken comes from the client app
FirebaseToken firebaseToken = null;
try {
Task<FirebaseToken> authTask = FirebaseAuth.getInstance().verifyIdToken(token);
Tasks.await(authTask);
firebaseToken = authTask.getResult();
} catch (Exception e) {
authenticationResultListener.onAuthenticationFailure();
}
uid = firebaseToken.getUid();
System.out.println("Uid= " + uid);
authenticationResultListener.onAuthenticationSuccess();
}
}