Btukfyl

I'm trying to use the jackson-kotlin integration. Mostly it works nice but I'm having trouble with deserializing generic types. I tried to adapt the answer to this question: Jackson - Deserialize using generic class

    // create an object mapper

    val jsonFactory = JsonFactory()

    jsonFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_TARGET, false)

    jsonFactory.configure(JsonParser.Feature.IGNORE_UNDEFINED, true)



    val objectMapper = ObjectMapper(jsonFactory)

    objectMapper.findAndRegisterModules()

    objectMapper.propertyNamingStrategy = PropertyNamingStrategy.SnakeCaseStrategy()

        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL)



    // simple generic type

    data class Inner(val meaningOfLife: Int)

    data class Outer<T>(val inner: T)



    val outer = Outer(Inner(42))



    val serialized = objectMapper.stringify(outer, true)

    println(serialized)



    // deserializing does not work using:

    // https://stackoverflow.com/questions/11664894/jackson-deserialize-using-generic-class

    val parsed = objectMapper.readValue<Outer<Inner>>(serialized, objectMapper.typeFactory.constructParametricType(Outer::class.java,Inner::class.java))

This throws an exception:

com.fasterxml.jackson.databind.JsonMappingException: Cannot deserialize Class io.inbot.common.ObjectMapperTest$should handle generics$Outer (of type local/anonymous) as a Bean

 at [Source: (String)"{

  "inner" : {

    "meaning_of_life" : 42

  }

}"; line: 1, column: 1]



    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:306)

    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:268)

    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)

    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)

    at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:477)

    at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4190)

    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4009)

    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3042)

    at io.inbot.common.ObjectMapperTest.should handle generics(ObjectMapperTest.kt:22)

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:498)

    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:124)

    at org.testng.internal.Invoker.invokeMethod(Invoker.java:580)

    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:716)

    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:988)

    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:125)

    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:109)

    at org.testng.TestRunner.privateRun(TestRunner.java:648)

    at org.testng.TestRunner.run(TestRunner.java:505)

    at org.testng.SuiteRunner.runTest(SuiteRunner.java:455)

    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:450)

    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:415)

    at org.testng.SuiteRunner.run(SuiteRunner.java:364)

    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)

    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:84)

    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1208)

    at org.testng.TestNG.runSuitesLocally(TestNG.java:1137)

    at org.testng.TestNG.runSuites(TestNG.java:1049)

    at org.testng.TestNG.run(TestNG.java:1017)

    at org.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:72)

    at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:123)

Caused by: java.lang.IllegalArgumentException: Cannot deserialize Class io.inbot.common.ObjectMapperTest$should handle generics$Outer (of type local/anonymous) as a Bean

    at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.isPotentialBeanType(BeanDeserializerFactory.java:877)

    at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:131)

    at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:411)

    at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:349)

    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)

    ... 31 more

Obviously the jackson plugin for kotlin does not handle this. Is there a workaround for this or a different way of doing this?

BTW. the stringify function is a simple extension function I added for ObjectMapper that takes care of the boilerplate code:

/**

 * Serializes [value] to a string. Pretty prints if [pretty] is set.

 */

fun <T> ObjectMapper.stringify(value: T, pretty: Boolean = false): String {

    val bos = ByteArrayOutputStream()

    val writer = OutputStreamWriter(bos, StandardCharsets.UTF_8)

    if(pretty) {

        writerWithDefaultPrettyPrinter().writeValue(writer,value)

    } else {

        writeValue(writer, value)

    }

    writer.flush()

    bos.flush()

    return bos.toByteArray().toString(StandardCharsets.UTF_8)

}

UPDATE The code in the answer by @jayson-minard works. It turns out that the key difference with my code was that I defined the data classes inside the test method. Moving them outside to the top level fixes things. Putting a dataclass in a function was a bad idea to begin with.

Using 2.9.6 of Jackson and then also the master branch 2.9.8 of Jackson along with the current Jackson-Kotlin module, I added this test case which passes for both your version of the code, and the cleaner idiomatic version of the code.

Note that I updated the stringify method to be more idiomatic as well, but this would not affect the test.

Your call to readValue is also more complicated than neccessary. Change:

val parsed = objectMapper.readValue<Outer<Inner>>(serialized, objectMapper.typeFactory.constructParametricType(Outer::class.java, Inner::class.java))

to simply:

val parsed = objectMapper.readValue<Outer<Inner>>(serialized)    

This is the full passing tests:

class TestStackOverflow53499407 {

    data class Inner(val meaningOfLife: Int)

    data class Outer<T>(val inner: T)



    fun <T> ObjectMapper.stringify(value: T, pretty: Boolean = false): String {

        StringWriter().use { writer ->

            if (pretty) {

                writerWithDefaultPrettyPrinter().writeValue(writer, value)

            } else {

                writeValue(writer, value)

            }

            return writer.toString()

        }

    }



    @Test

    fun test53499407_cleanTest() {

        val outer = Outer(Inner(42))

        val objectMapper = jacksonObjectMapper()



        val serialized = objectMapper.stringify(outer, true)

        println(serialized)



        val parsed = objectMapper.readValue<Outer<Inner>>(serialized)

        assertEquals(42, parsed.inner.meaningOfLife)

    }



    @Test

    fun test53499407_idiomatic_tweek() {

        val outer = Outer(Inner(42))



        val jsonFactory = JsonFactory()

        jsonFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_TARGET, false)

        jsonFactory.configure(JsonParser.Feature.IGNORE_UNDEFINED, true)



        val objectMapper = ObjectMapper(jsonFactory)

        objectMapper.findAndRegisterModules()

        objectMapper.propertyNamingStrategy = PropertyNamingStrategy.SnakeCaseStrategy()

        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL)



        val serialized = objectMapper.stringify(outer, true)

        println(serialized)



        // This line changed to be idiomatic

        val parsed = objectMapper.readValue<Outer<Inner>>(serialized)

        assertEquals(42, parsed.inner.meaningOfLife)

    }



    @Test

    fun test53499407_as_written_in_stackoverflow() {

        val outer = Outer(Inner(42))



        val jsonFactory = JsonFactory()

        jsonFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_TARGET, false)

        jsonFactory.configure(JsonParser.Feature.IGNORE_UNDEFINED, true)



        val objectMapper = ObjectMapper(jsonFactory)

        objectMapper.findAndRegisterModules()

        objectMapper.propertyNamingStrategy = PropertyNamingStrategy.SnakeCaseStrategy()

        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL)



        val serialized = objectMapper.stringify(outer, true)

        println(serialized)



        // deserializing does not work using:

        // https://stackoverflow.com/questions/11664894/jackson-deserialize-using-generic-class

        val parsed = objectMapper.readValue<Outer<Inner>>(serialized, objectMapper.typeFactory.constructParametricType(Outer::class.java, Inner::class.java))

        assertEquals(42, parsed.inner.meaningOfLife)

    }

}