I'm new to Java, and I'm wondering how to deserialize an empty JSON array into an empty Java object of type TreeMap<String, MyOtherClass>
.
Currently, I'm attempting to deserialize a JSON file with an array of objects, and each object into a class called MyClass
. The class is roughly as follows:
@JsonIgnoreProperties(ignoreUnknown = true)
public class MyClass {
private final String propertyOne;
private final String propertyTwo;
private final String propertyThree;
@JsonSerialize(contentAs = MyOtherClass.class)
@JsonDeserialize(contentAs = MyOtherClass.class)
TreeMap<String, MyOtherClass> otherThings = new TreeMap<>();
@JsonCreator
public MyClass(
@JsonProperty("propertyOne") String propertyOne,
@JsonProperty("propertyTwo") String propertyTwo,
@JsonProperty("propertyThree") String propertyThree) {
this.propertyOne = propertyOne;
this.propertyTwo = propertyTwo;
this.propertyThree = propertyThree;
// Getters and setters below
@JsonSetter("otherThings")
public void setOtherThings() {
if (this.otherThings == null || this.otherThings.isEmpty()) {
this.otherThings = new TreeMap<>();
}
}
}
}
One of the entries in the original JSON is this field otherThings
. I've represented this entry using MyOtherClass
, which handles the properties that otherThings
could contain.
Currently, this works perfect for serialization, and for deserialization when otherThings
is populated. However, when I have something like the following:
{
"propertyOne": "This is propertyOne!",
"propertyTwo": "This is propertyTwo!",
"propertyThree": "This is propertyThree!",
"otherThings": []
}
I get the following stack trace:
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.TreeMap<java.lang.String,org.something.model.MyOtherClass>` from Array value (token `JsonToken.START_ARRAY`)
at [Source: (URL); line: 7, column: 14] (through reference chain: java.util.ArrayList[0]->org.something.model.Order["lines"])
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1741)
at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1515)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer._deserializeFromArray(StdDeserializer.java:222)
at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:447)
at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:32)
at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:277)
at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:462)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1405)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:351)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:184)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:355)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:244)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:28)
at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:322)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4675)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3572)
at org.something.model.MyClass.populateMyClassFromJson(MyClass.java:148)
at org.something.service.MyClassService.displayMyClassObject(MyClassService.java:96)
at Main.main(Main.java:9)
I've tried:
- Using
ObjectMapper.enable(DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT)
, but that doesn't really help sinceotherThings
gets instantiated asnull
. - Using the
JsonSetter
forsetOtherThings
you see above. This has to be careful because I don't want to overwriteotherThings
if it already contains things inside of it.
EDIT: Here's also the method populateMyClassFromJson
if it helps:
public void populateMyClassFromJson() throws IOException {
List<MyClass> myClassList = mapper.readValue(new File("/path/to/my_classes.json"), new TypeReference<>() {});
Map<String, MyClass> myClassMap = myClassList.stream().collect(Collectors.toMap(MyClass::getId, Function.identity()));
myClassTreeMap.putAll(myClassMap);
}
CodePudding user response:
Just to summarize (I believe it was clear from the start): as error states the problem is that Jackson tries to deserialize field as TreeMap which is not going to work since the in JSON there is an array []
.
However your setter seems a bit odd to me. I believe you should have something like this (updated based on your comment and update):
@JsonSetter("otherThings")
public void setOtherThings(MyOtherClass[] arr) {
this.otherThings = List.of(Optional.ofNullable(arr)
.orElse(new MyOtherClass[0])).stream()
.collect(Collectors.toMap(MyOtherClass::getId, Function.identity(),
(o1, o2) -> o1, TreeMap::new));
}
Of course you should also handle the case when the array is not empty.