How to Deserialize an Array of Objects in Jackson using Java?

Deserializing an Array of Objects with Jackson

Jackson documentation claims support for deserializing arrays of objects, but the specific syntax might be unclear. Let's explore two approaches for deserializing an array of objects.

Serialization Considerations

Consider the following JSON input for an array of objects:

[{
    "id" : "junk",
    "stuff" : "things"
},
{
    "id" : "spam",
    "stuff" : "eggs"
}]

Deserialization Approach 1: As Array

Instantiate an ObjectMapper and use readValue to deserialize the input as an array of the target object type:

// Instantiate an ObjectMapper
ObjectMapper mapper = new ObjectMapper();

// Deserialize JSON into an array of MyClass objects
MyClass[] myObjects = mapper.readValue(jsonInput, MyClass[].class);

Deserialization Approach 2: As List

To deserialize the input as a list, one can use new TypeReference or constructCollectionType:

Option a: Using TypeReference

// Create TypeReference for a list of MyClass objects
TypeReference<List<MyClass>> typeRef = new TypeReference<List<MyClass>>() {};

// Deserialize JSON input using the TypeReference
List<MyClass> myObjects = mapper.readValue(jsonInput, typeRef);

Option b: Using constructCollectionType

// Create a CollectionType for a list of MyClass objects
JavaType type = mapper.getTypeFactory().constructCollectionType(List.class, MyClass.class);

// Deserialize JSON input using the CollectionType
List<MyClass> myObjects = mapper.readValue(jsonInput, type);

With these approaches, you can flexibly deserialize arrays of objects into desired data structures in Java using Jackson.

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