JAVA

java firebase syncrhonous data read

// create a java.util.concurrent.Semaphore with 0 initial permits
final Semaphore semaphore = new Semaphore(0);

// attach a value listener to a Firebase reference
ref.addValueEventListener(new ValueEventListener() {
    // onDataChange will execute when the current value loaded and whenever it changes
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // TODO: do whatever you need to do with the dataSnapshot

        // tell the caller that we're done
        semaphore.release();
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

// wait until the onDataChange callback has released the semaphore
semaphore.acquire();

// send our response message
ref.push().setValue("Oh really? Here is what I think of that");