How to make multiple consecutive GET requests from Android using OkHttp?

Question

Android

There is storage on Yandex.Cloud.
It has over 1000 items.
In order to get them all, you need to make several consecutive GET requests, because a maximum of 1000 objects can come in one request.
Question: how to make sequential requests on Android? Preferably in Java using OkHttp
Link to help for JS

Answer 1

RxJava or Java 8 Stream is well suited for such tasks. Better than RxJava, as it can multithread. Both APIs are designed for convenient work with input streams. I don’t know the OkHttp API, because I didn’t write shop clients and a typical one. Here is a tutorial: https://www.vogella.com/tutorials/RxJava/article.html
In general, if you want something simple, make a queue, something like:

public class Result {
  
  public final static int NEXT = 1;
  public final static int FINISH = 2;
  public final static int ERROR = 3;
  public final static int NO_NEXT = 4;

  public final int result;
  public final String someData;
  public final Throwable tr;
  
  public Result(int result, String someData, Throwable tr) {
    this.result = result;
    this.someData = someData;
    this.tr = tr;
  }
}

public abstract class Operation {

  final Queue queue;
  
  public Operation(Queue queue) {
    this.queue = queue;
  }

    public interface OnExecuted {
        void onExecution(Result result);
    }
  
    void execute() {
    	executeOperation((result) -> {
        		queue.addResult(result);
        		queue.next();
            }
        );
    }	
    
    abstract public void executeOperation(OnExecuted onExecuted);
}

public class Queue {
  
  public interface OnQueueFinish {
    void onQueueFinish(LinkedList<Result> results);
  }

  final LinkedList<Result> results = new LinkedList<>();
  final LinkedList<Operation> operations = new LinkedList<>();
  
  private int currentOperation = -1;
  
  final OnQueueFinish onFinish;
  
  public Queue(OnQueueFinish onFinish) {
    this.onFinish = onFinish;
  }
  
  public void addOperation(Operation operation) {
    operations.addLast(operation);
  }
  
  void addResult(Result result) {
    results.addLast(result);
    if(result.result > NEXT) {
      onFinish.onQueueFinish(results);
    }
  }
  
  public void next() {
    currentOperation++;
    if(currentOperation >= operations.size()) {
      addResult(new Result(NO_NEXT, null, null));
    }
    operations.get(currentOperation).execute();
  }
}

public class GetOperation extends Operation {

  final URI uri;
  final int onSuccessCode;
  final int onErrorCode;
  
  public GetOperation(Queue queue, URI uri, int onSuccessCode, int onErrorCode) {
    super(queue);
    this.uri = uri;
    this.onErrorCode = onErrorCode;
    this.onSuccessCode = onSuccessCode;
  }

  @Override
  public void executeOperation(OnExecuted onExecuted) {
    // На замыканиях
    SomeApi.get(uri)
         .onSuccess((data, code) -> onExecuted.onExecution(new Result(onSuccessCode, data, null)))
         .onError((code, tr) -> onExecuted.onExecution(new Result(onErrorCode, data, null))).run();
    // По обычному
    try {
      Response r = SomeApi.get(uri);
      onExecuted.onExecution(new Result(onSuccessCode, r.getData(), null));
    } catch (Throwable tr) {
      onExecuted.onExecution(new Result(onErrorCode, null, null));
    }
  }
}

public class Something {

  public Something() {}
  
  void wreeee() {
    Queue queue = new Queue(this::onQueueFinished);
    // очередь будет продолжена даже при ошибке
    queue.addOperation(new GetOperation(queue, new URI("http://somehub.com"), NEXT, NEXT));
    // в случае ошибки очередь остановится
    queue.addOperation(new GetOperation(queue, new URI("http://oldwomenneedyou.com"), NEXT, ERROR));
    // останавливаем очередь на последнем элементе вручную
    queue.addOperation(new GetOperation(queue, new URI("http://brotherlove.com"), FINISH, ERROR));
    // Тут запускаем очередь
    queue.next();
  }
  
  void onQueueFinished(LinkedList<Result> results) {
    // Тут список результатов обрабатываете, ошибки и т.п.
  }

}

With synchronizations, annotations of contracts, exceptions, timeouts and other husks, you will figure it out yourself.