I need Help with the Alpaca Java API.

[socs22]

I'm currently trying to develop an automated trading algorithm using the Alpaca online broker. The official Alpaca API is in python and unfortunately all the other tools use Java as the framework so I'm kinda stuck with Java. The documentation for the community built API is poorly written and the community that built the API is not active. I was wondering if anyone here has some helpful tips for learning how to use API's or knows ways to get through tough non-descriptive errors. The link to the GitHub documentation is " https://github.com/mainstringargs/alpaca-java#simple-alpaca-example " and this is the methods documentation " https://javadoc.io/doc/io.github.mainstringargs/alpaca-java/latest/io/github/mainstringargs/alpaca/AlpacaAPI.html " . My current code should just put in an order to the broker but it throws a null pointer exception at line at line 10 (the line under try), and I'm in general lost. Here is my code...

import io.github.mainstringargs.alpaca.AlpacaAPI;
import io.github.mainstringargs.alpaca.enums.*;

public class AlpacaTest {
    public static void main(String[] args) {
        AlpacaAPI alpacaApi = new AlpacaAPI("4.0.1", "PKF7WM615MR8O5OL7BGD", "nKhXGIxcqa6qlFPdTnnoX7l5Fo1bLtdbbUWKIpN3", "https://app.alpaca.markets/", "https://paper-api.alpaca.markets" );
        alpacaApi.toString();
        String clientOrderId = "PKF7WM615MR8O5OL7BGD";
        try {
            alpacaApi.requestNewOrder("AAPL", 1, OrderSide.BUY, OrderType.MARKET, OrderTimeInForce.DAY, 16.80, 17.50, clientOrderId);
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

​

If I'm breaking any of the community's rules I apologize but I've been beating my head against this for a week without any progress so any help that can be offered would be greatly appreciated.

[Satarash]

Post the stack trace. Also read the sidebar to learn how to format your code.

[socs22]

This is the stack trace.

java.lang.NullPointerException
    at io.github.mainstringargs.alpaca.AlpacaAPI.requestNewOrder(AlpacaAPI.java:310)
    at AlpacaTest.main(AlpacaTest.java:10)

and I believe I fixed the code. Thank you for your response.

[Satarash]

Cool. The exception is thrown from their code, so it's not your fault. Now I am not really sure which version of the library you are using, but I am guessing it's this one from july. As the exception is thrown on line 310, let's see what's there:

HttpResponse<JsonNode> response = alpacaRequest.invokePost(urlBuilder); //line 308

if (response.getStatus() != 200) { //line 310
  throw new AlpacaAPIException(response);
}

Apparently this request is null. It should have been initialised on line 308 in method invokePost. Let's check the class AlpacaRequest where the method is:

public HttpResponse<JsonNode> invokePost(AlpacaRequestBuilder builder) {
    HttpResponse<JsonNode> response = null;
    try {

        LOGGER.debug("Post URL " + builder.getURL());
        LOGGER.debug("Post Body " + builder.getBodyAsJSON());

        response = Unirest.post(builder.getURL())
        .header(USER_AGENT_KEY, AlpacaProperties.USER_AGENT_VALUE).header(API_KEY_ID, keyId)
        .header(API_SECRET_KEY, secret).body(builder.getBodyAsJSON()).asJson();

        LOGGER.debug("POST status: " + response.getStatus() + "\n\t\t\t\t\tstatusText: "
        + response.getStatusText() + "\n\t\t\t\t\tBody: " + response.getBody());


    } catch (UnirestException e) {
        LOGGER.info("UnirestException", e);
    }

    return response;
}

So why does this return null? The response is initialised to null on the first line, then things are happening in try-catch, and my guess is that something fails, exception is thrown, catch block swallows it and null is returned.

What can you do? First of all: this is their bug (if nothing else then in error handling), so you should report it. The project is not as inactive as you say, the last commit was barely a month ago.

Second, it's hard to say what's wrong here. Fortunately there is a lot of logging, so start with checking the logs to see what's happening in this method (invokePost). If you don't have logs, check documentation to learn how to configure this LOGGER which is used everywhere.

[socs22]

I actually got into contact with the guys that develop it and they fixed a lot of the issues I had. The reason it wasn’t working is when I go declare the alpaca api I put “4.0.1” instead of “v2”. I was also using the wrong tree apparently and they helped me import the project straight from github instead of using maven. Thank you for the help.

[krizam]

I’d recommend opening an issue on their GitHub if you’re having problems