Re: [geomesa-users] Compilaiton error in Java when applying "map" to an

[Jim Hughes <jnh5y@xxxxxxxx>]

Hi Luca,

Great question.  Sadly, I haven't used Spark from Java, nor have I used 
Java 8.  That said, from some quick research and knowing Scala, I have a 
suggestion to try.

To me, the error is saying that the Java 8 lambda isn't being understood 
as a scala.Function1.  There may be some way to help cross that gap, but 
the Java compiler isn't going to sort that out for you.

Defining the scala.Function1 directly should work though:

import scala.runtime.AbstractFunction1;

    public static RDD<Object> loadFromGeoMesaTable(Configuration conf, 
SparkContext sc) {

        scala.Function1 transform = new 
AbstractFunction1<SimpleFeature, Tweet>() {
            public Tweet apply(SimpleFeature feature) {
                return new Tweet(feature);
            }
        };

        RDD<Object> rddOut = GeoMesaSpark.rdd(conf, sc, null, null, false)
                .map( transform, 
scala.reflect.ClassTag$.MODULE$.apply(Tweet.class));

        return rddOut;
    }

At the very least, this should be closer; I was able to get this to compile.

Cheers,

Jim

On 05/08/2015 05:02 AM, Luca Morandini wrote:
> I am trying to generate an RDD of Objects from an RDD of 
> SimpleFeatures, but I was not able to find a way to do it.
>
> Here's the failing code:
> public static RDD<Object> loadFromGeoMesaTable(Configuration conf,
>       SparkContext sc, GeoMesaOptions options) {
>
>     RDD<Object> rddOut = GeoMesaSpark.rdd(conf, sc,
>         TweetFeatureStore.getFeatureType(options).getDataStore(), 
> null, false)
>         .map((feat) -> {
>           return new Tweet(feat);
>         }, scala.reflect.ClassTag$.MODULE$.apply(Object.class));
>
>     return rddOut;
>   }
>
> Here's the compilation error:
> method map in class org.apache.spark.rdd.RDD<T> cannot be applied to 
> given types;
> [ERROR] required: 
> scala.Function1<org.opengis.feature.simple.SimpleFeature,U>,scala.reflect.ClassTag<U>
> [ERROR] found: (feat)->{ [...]t); 
> },scala.reflect.ClassTag<java.lang.Object>
> [ERROR] reason: cannot infer type-variable(s) U,T
> [ERROR] (argument mismatch; scala.Function1 is not a functional interface
> [ERROR] multiple non-overriding abstract methods found in interface 
> scala.Function1)
>
> Any help much appreciated,
>
> Luca Morandini
> Data Architect - AURIN project
> Melbourne eResearch Group
> Department of Computing and Information Systems
> University of Melbourne
> Tel. +61 03 903 58 380
> Skype: lmorandini
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