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POStrange deserializing problems with generic types using Scala and Jackson and java.lang.Integer or scala.Int
 

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  1. POStrange deserializing problems with generic types using Scala and Jackson and java.lang.Integer or scala.Int
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    <p>We all know that generic types are subject to type erasure under Java and Scala. But we ran into a strange problem in Scala using Jackson and the Scala Jackson Module.</p> <p>I created a small test to show the problem.</p> <pre><code>import com.fasterxml.jackson.databind.ObjectMapper import com.fasterxml.jackson.module.scala.DefaultScalaModule object GenericTest { case class TestWithInt(id: Option[Int]) case class TestWithInteger(id: Option[Integer]) def main(args: Array[String]) { val mapper = new ObjectMapper() mapper.registerModule(DefaultScalaModule) // Test with scala's Int val test = mapper.readValue[TestWithInt]("""{ "id" : 5 }""", classOf[TestWithInt]) print("Test 1: ") println(test.id.get + 1) val test2 = mapper.readValue[TestWithInt]("""{ "id" : "5" }""", classOf[TestWithInt]) print("Test 2: ") try { println(test2.id.get + 1) } catch { case e: ClassCastException =&gt; println(e.getMessage) } // Test with java.lang.Integer val test3 = mapper.readValue[TestWithInteger]("""{ "id" : 5 }""", classOf[TestWithInteger]) print("Test 3: ") println(test3.id.get + 1) val test4 = mapper.readValue[TestWithInteger]("""{ "id" : "5" }""", classOf[TestWithInteger]) print("Test 4: ") println(test4.id.get + 1) } } </code></pre> <p>The output of the above is:</p> <pre><code>Test 1: 6 Test 2: java.lang.String cannot be cast to java.lang.Integer Test 3: 6 Test 4: 6 </code></pre> <p>Where does this different kind of behaviour come from? Generic Type Erasure, Jackson, Jackson Scala Module?</p>
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    1. COI'm not familiar enough with Scala to say, but my guess is that Jackson has a built-in converter that knows how to handle the conversion for the Java type but not Scala's.
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    2. COHmm, maybe ...created an issue for that, cross referencing this question: https://github.com/FasterXML/jackson-module-scala/issues/104
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