Jackson ObjectMapper deserialize object with array

Question

There are some similar questions here and here, but they don't quite match my situation. My JSON string consists of an object with an array:

{
  "data": [
    {
      "id": 1,
      "title": "Sample training",
      "date": "2016-10-03 10:00:00",
      "subscription": "2016-09-20 12:34:50"
    },
    {
      "id": 2,
      "title": "Second training",
      "date": "2016-10-06 10:00:00",
      "subscription": "2016-09-20 12:54:50"
    }
  ]
}

Each object in the array is a Java bean:

public class TrainingInfo {

    private int id;
    private String title;
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm:ss")
    private LocalDateTime date;
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm:ss")
    private LocalDateTime subscription;

    // Consructors, getters and setters omitted 
    // ...
}

I am able to read a single TrainingInfo with:

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
TrainingInfo training = mapper.readValue(jsonTrainingInfo, TrainingInfo.class);

But I am not able to read the whole array. I have tried to create a new Java bean just containng an array and read it, like so:

private class TrainingsArray {
    private TrainingInfo[] data;

    public TrainingInfo[] getData() {
        return data;
    }

    public void setData(TrainingInfo[] data) {
        this.data = data;
    }
}

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
TrainingsArray trainings = mapper.readValue(jsonTrainingsArray, TrainingsArray.class);

But this just throws an IOException. What am I missing?

UPDATE: The exception thrown:

com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of JsonMapperTest$TrainingsArray: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: {
  "data": [
    {
      "id": 1,
      "title": "Sample training",
      "date": "2016-10-03 10:00:00",
      "subscription": "2016-09-20 12:34:50"
    },
    {
      "id": 2,
      "title": "Second training",
      "date": "2016-10-06 10:00:00",
      "subscription": "2016-09-20 12:54:50"
    }
  ]
}; line: 2, column: 3]

    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:270)
    at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1456)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1205)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:314)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3798)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2842)
    at JsonMapperTest.shouldMapJsonResponseToTrainingsArray(JsonMapperTest.java:90)
    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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
    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 com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Make your TrainingsArray class a top-level class, or at least a static nested class instead of an inner class. An inner class needs a reference to its outer instance to be constructed. Jackson would have to create an instance of JsonMapperTest. And it won't do that. — JB Nizet, Nov 25 '16 at 09:54
make your class `TrainingsArray` accessible by making it `public` instead of `private`, if you want to keep it as an inner class make it `static` too — Nicolas Filotto, Nov 25 '16 at 10:01
JB and Nicolas are correct, inner class may be a problem as well, I assumed it was a normal class... — grape_mao, Nov 25 '16 at 10:09
@grape_mao @Nicolas Filotto @JB Nizet you were all right. It was enough to change the class from `private` to `public` to make the test work. I just didn't think that would affect... If any of you makes an actual answer, I'd be happy to accept it. — houcros, Nov 25 '16 at 10:09
Nowadays some people write long answers to simple questions just to earn more points, which is meaningless and a waste of time for me. — grape_mao, Nov 25 '16 at 10:11
I agree, but I believe it is still nice to have an answer, even if it's a short one like "Make your class public instead of private". For future readers, it shows straight away that a solution was found, however trivial it might have been :) — houcros, Nov 25 '16 at 10:15

score 1 · Accepted Answer · answered Dec 06 '16 at 20:31

1

However silly this might be, the solution was to make the class TrainingsArray public.

answered Dec 06 '16 at 20:31

houcros

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Jackson ObjectMapper deserialize object with array

1 Answers1