scala future null pointer match error

Question

New to scala futures I try to call a web service like

wsClient.url(baseUrl + url).withHeaders("Content-Type" -> "application/json").post(dataForR).flatMap(parseOutlierResponse)

using ply-ws library

I validate & map the response as follows https://gist.github.com/geoHeil/943a18d43279762ad4cdfe9aa2e40770

The main thing is:

Await.result(callAMethodCallingTheFirstSnippet, 5.minutes)

Strangely this works just fine in the repl. However if run via sbt run I get a NullPointer Exception. I already verified the JSON response manually. It validates like a breeze. Even the mapping works great. However, there must be a problem with the futures I am using. But I am not sure what is wrong. It seems like the flatMap method is called before there already is a result.

Interestingly if I do not await the result there is no null-pointer exception, but the parsed result is displayed correctly (however, the program does not exit). But there, where I really use this code, I somehow need to await the successful completion to further deal with it.

Below you will find an illustration of the problem

Sounds like there is no response JSON. Did you try printing out the response body? — joesan, May 21 '16 at 05:12
As mentioned above when run in the REPL it really works and the `Await.result(result, 10.minutes)` maps the response just fine. So yes there is a response when printed like `wsClient.url(baseUrl + url).withHeaders("Content-Type" -> "application/json").post(dataForR).map(response => println(response.body))` — Georg Heiler, May 21 '16 at 05:37
I used the printed response.body to obtain the data. Then again the mapping works great `val dataP = Json.parse(manuallyExtractedData).validate[Seq[OutlierPortal]].fold( error => { println(s"Unable to parse response: $error") Future.failed(new RuntimeException("parse-json-failed")) }, outlierResponse => Future.successful(outlierResponse.map { _.toMap }) ) dataP.foreach(println)` — Georg Heiler, May 21 '16 at 05:52
@sparkr please see the minimum example and the latest screenshot. — Georg Heiler, May 22 '16 at 05:52

score 0 · Answer 1 · answered May 22 '16 at 05:58

0

I do not see any major concern with your code! I made a small test with the following code bit and it seems to be working perfectly, both in the REPL and when using sbt run:

    WS.clientUrl(s"http://$hostName/api/put").withHeaders(jsonHeaders: _*).post(body).map { r =>
      if (r.status >= 400)
        logger.warn(s"Invalid http response status: ${r.status} \n ${r.body}")
      else
        logger.debug(s"Successfully persisted data. Http response ${r.status}")
    }

answered May 22 '16 at 05:58

joesan

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indeed your code prints the response. However if the mapping like `r.json.validate[Seq[OutlierPortal]].fold( error => { println(s"Unable to parse response: $error") (new RuntimeException("parse-json-failed")) }, outlierResponse => outlierResponse.map { _.toMap }` is added I get the null pointer from above. – Georg Heiler May 22 '16 at 12:33

Georg Heiler · Accepted Answer · 2016-05-23T06:37:04.353

0

After more and more debugging I found that some implicits were in the wrong scope and the order of dependent case-classes was wrong. After moving them into the correct scope (the method performing the request) the null-pointer exception is fixed.

I could only find the "real" error after changing from flatmap to map which I find very strange. However, now both methods work fine.

edited May 23 '16 at 06:37

answered May 23 '16 at 06:11

Georg Heiler

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Just wondering, why do you wrap the results in `parseOutlierResponse` using Future.successful. This looks superfluous, you can just throw the exceptions and `map` the `post()`. – Manuel Bernhardt May 25 '16 at 21:05
Well starting out with futures I based my approach on https://github.com/studiodev/Mocky/blob/master/app/services/GithubRepository.scala and they use it like that. But I understand your point now. – Georg Heiler May 27 '16 at 08:08

scala future null pointer match error

2 Answers2