BTC-China getTrades() ClassCastException

[zholmes1]

I have the same issue with JustcoinExchange

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.xeiam.xchange.btcchina.dto.marketdata.BTCChinaTrade
at com.xeiam.xchange.btcchina.BTCChinaAdapters.adaptTrades(BTCChinaAdapters.java:125)

Then happens when the getTrades(CurrencyPair) method is called.

[timmolter]

Can you please try the latest snapshot jars and report back?

[zholmes1]

Yes, this occurs with the most recent snapshot JARS.
On Jul 12, 2014 5:38 AM, "Tim Molter" notifications@github.com wrote:

Can you please try the latest snapshot jars and report back?

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#517 (comment).

[sutra]

I cannot reproduce this problem either, by running com.xeiam.xchange.examples.btcchina.marketdata.BTCChinaTradesDemo.generic() on version f766bac

[zholmes1]

What version of Java are you using?
On Jul 13, 2014 10:19 AM, "Sutra Zhou" notifications@github.com wrote:

I cannot reproduce this problem either, by running
com.xeiam.xchange.examples.btcchina.marketdata.BTCChinaTradesDemo.generic()
on version f766bac
f766bac

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#517 (comment).

[sutra]

java version "1.6.0_65"
the same as specified in pom.xml

[zholmes1]

I had the same issue for Justcoin, and another user was able to get code
working on Java 8 that I wasn't able to with Java 7. Unfortunately
developing for Android doesn't give me any choices between Java versions.
On Jul 13, 2014 10:23 AM, "Sutra Zhou" notifications@github.com wrote:

java version "1.6.0_65"
the same as specified in pom.xml

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#517 (comment).

[sutra]

Cannot reproduced in Java 1.7 either.

[jpe42]

@zholmes1 Can you try out writing a custom deserializer for BTCChinaTrade that you can get working in your environment as well as a non-andriod vm? If you search the codebase for 'JsonDeserializer' you will find plenty of examples. This isn't a preferred solution as it is just more code to maintain. Otherwise this seems like it should be an issue with whatever version of Jackson you are using.

[zholmes1]

I didn't consider that it could be Jackson. I will add the correct version
when I get to my computer and see if that works.
On Jul 13, 2014 10:57 AM, "James Edwards" notifications@github.com wrote:

@zholmes1 https://github.com/zholmes1 Can you try out writing a custom
deserializer for BTCChinaTrade that you can get working in your environment
as well as a non-andriod vm? If you search the codebase for
'JsonDeserializer' you will find plenty of examples. This isn't a preferred
solution as it is just more code to maintain. Otherwise this seems like it
should be an issue with whatever version of Jackson you are using.

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#517 (comment).

[zholmes1]

Sorry for the delay. I updated Jackson to 2.3 and I am still having this issue.

[sutra]

I guess if we change the return type of com.xeiam.xchange.btcchina.BTCChina.getTrades(String, long, int) from List<BTCChinaTrade> to BTCChinaTrade[] will resolve this problem. That is because of the type erasure of Java's generic implementation. So in byte code level, the List<BTCChinaTrade> maybe(here maybe means different JVMs may have different implementations, even bugs, I am not sure about this in JVM spec) will be erased to List, then the type BTCChinaTrade lost, it will fail to LinkedHashMap in reflection.

  @GET
  @Path("data/historydata")
  public List<BTCChinaTrade> getTrades(
      @QueryParam("market") String market,
      @QueryParam("since") long since,
      @QueryParam("limit") int limit) throws IOException;

[timmolter]

can you post the exact line of code in BTCChinaAdapters that is throwing the error? The line number.

[timmolter]

Does running BTCChinaTradesDemo allow you to reproduce the error or is it only a call to the adapter method when run on Android that causes the error?

[timmolter]

I believe the issue is that in rescu (@mmazi) when the json is mapped to the return type defined in the rest interface method, it's not being correctly mapped to a List. In the case on for a certain Android JVM, it's getting mapped to a LinkedHashMap for some reason.

In RestMethodMetadata in rescu the return type is determined with this call:

method.getGenericReturnType()

There's some more possibly useful info here that could be used perhaps in rescu to get a more accurate return type: http://tutorials.jenkov.com/java-reflection/generics.html. If possible a solution like this in rescu would be more robust.

However to get this working now, you can do what @sutra suggested and change the return type to BTCChinaTrade[] or also possibly ArrayList<BTCChinaTrade>.

If you look in Justcoin, the rest interface methods also return Lists. In implementations where an array is returned you're not seeing this issue.

[sutra]

Found it was using array before 31cf69a, how about changing back to use array, and avoid using generic type for return type of getTicker too. @jamespedwards42

[timmolter]

It'd be easier to try ArrayList first. i bet that would work.

[sutra]

I don't think List or ArrayList is a good choice, but array, as it should be readonly, we do not need to add/remove elements.

[zholmes1]

Hey, I'm working on a Poloniex implementation and I was getting this error when I was parsing the returned JSON as a List<PoloniexPublicTrade>.

A simple switch to PoloniexPublicTrade[] solved the problem completely.

[jpe42]

I would be willing to help out with migrating all of the exchanges to use primitive arrays. I think we could just throw up a wiki page and start claiming each exchange one by one.

[timmolter]

That's excellent! As a committer, can you create/edit Wiki pages?

[jpe42]

https://github.com/timmolter/XChange/wiki/List-to-Primitive-Array-Migration

[mmazi]

I've opened an issue in rescu for @timmolter 's suggestion.

[timmolter]

@zholmes1 This should now be fixed in the latest snapshot version. Can you please test and close this issue if it's OK?

[zholmes1]

Yes I will test it out tonight.
On Aug 11, 2014 9:31 AM, "Tim Molter" notifications@github.com wrote:

@zholmes1 https://github.com/zholmes1 This should now be fixed in the
latest snapshot version. Can you please test and close this issue if it's
OK?

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#517 (comment).

[zholmes1]

Everything is working perfectly.