How to use Jackson to deserialise an array of objects

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The Jackson data binding documentation indicates that Jackson supports deserialising "Arrays of all supported types" but I can't figure out the exact syntax for this.

For a single object I would do this:

//json input
{
    "id" : "junk",
    "stuff" : "things"
}

//Java
MyClass instance = objectMapper.readValue(json, MyClass.class);

Now for an array I want to do this:

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

//Java
List<MyClass> entries = ?

Anyone know if there is a magic missing command? If not then what is the solution?

First create a mapper :

import com.fasterxml.jackson.databind.ObjectMapper;// in play 2.3
ObjectMapper mapper = new ObjectMapper();

As Array:

MyClass[] myObjects = mapper.readValue(json, MyClass[].class);

As List:

List<MyClass> myObjects = mapper.readValue(jsonInput, new TypeReference<List<MyClass>>(){});

Another way to specify the List type:

List<MyClass> myObjects = mapper.readValue(jsonInput, mapper.getTypeFactory().constructCollectionType(List.class, MyClass.class));

How to use Jackson to deserialize an array of objects, 1 Answer. import com.fasterxml.jackson.databind.ObjectMapper;// in play 2.3. ObjectMapper mapper = new ObjectMapper(); List<MyClass> myObjects = mapper.readValue(jsonInput, new TypeReference<List<MyClass>>(){}); List<MyClass> myObjects = mapper. readValue(jsonInput, mapper. MyClass[] myObjects = mapper. For Array of Objects. Browse other questions tagged java android arrays json jackson or ask your own question. How to use Jackson to deserialise an array of

From Eugene Tskhovrebov

List<MyClass> myObjects = Arrays.asList(mapper.readValue(json, MyClass[].class))

This solution seems to be the best for me

Jackson, This tutorial will show how to deserialize a JSON Array to a Java Array or you can do with the Jackson 2 – head on over to the main Jackson tutorial. assertThat((Object) asList.get( 0 ), instanceOf(LinkedHashMap. class ));. Using Jackson to deserialise an array of object . Using Jackson to deserialise an array of object. Home. Community . Categories . Java .

For Generic Implementation:

public static <T> List<T> parseJsonArray(String json,
                                         Class<T> classOnWhichArrayIsDefined) 
                                         throws IOException, ClassNotFoundException {
   ObjectMapper mapper = new ObjectMapper();
   Class<T[]> arrayClass = (Class<T[]>) Class.forName("[L" + classOnWhichArrayIsDefined.getName() + ";");
   T[] objects = mapper.readValue(json, arrayClass);
   return Arrays.asList(objects);
}

Deserialize JSON collection to collection of Objects using Jackson, If there is a more complex nested structure, you will want to deserialize to a Map. We will look at examples of both. Deserializing JSON array. String jsonString = "[{​\  Jackson is one of the most common Java libraries for processing JSON. It is used for reading and writing JSON among other tasks. Using Jackson, you can easily handle automatic conversion from Java objects to JSON and back. In this article, we delve into some common Jackson usage patterns.

First create an instance of ObjectReader which is thread-safe.

ObjectMapper objectMapper = new ObjectMapper();
ObjectReader objectReader = objectMapper.reader().forType(new TypeReference<List<MyClass>>(){});

Then use it :

List<MyClass> result = objectReader.readValue(inputStream);

Jackson – Convert JSON array string to List – Mkyong.com, Few Jackson examples to convert a JSON array string to a List \"age\":38}]"; // 1. convert JSON array to Array objects Person[] pp1 = mapper. This tutorial will show how to deserialize a JSON Array to a Java Array or Collection with Jackson 2. If you want to dig deeper and learn other cool things you can do with the Jackson 2 – head on over to the main Jackson tutorial. 2. Unmarshall to Array. Jackson can easily deserialize to a Java Array:

try {
    ObjectMapper mapper = new ObjectMapper();
    JsonFactory f = new JsonFactory();
    List<User> lstUser = null;
    JsonParser jp = f.createJsonParser(new File("C:\\maven\\user.json"));
    TypeReference<List<User>> tRef = new TypeReference<List<User>>() {};
    lstUser = mapper.readValue(jp, tRef);
    for (User user : lstUser) {
        System.out.println(user.toString());
    }

} catch (JsonGenerationException e) {
    e.printStackTrace();
} catch (JsonMappingException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

Jackson ObjectMapper, The Jackson ObjectMapper can read JSON into Java objects and write into Java objects is also referred to as to deserialize Java objects from JSON. Here is an example of reading an object array from a JSON array string: deserialize arrayList of objects in jakson json. how can de-serialize rest request with json object having array of objects . use Jackson to deserialise an

Using Jackson for JSON Serialization and Deserialization, Serializing an array of objects to JSON is straightforward. 1. 2. 3. 4. 5. ObjectMapper mapper =  Then use ObjectMapper to convert your JSON to objects. @Oleg indicated that you can use: new ObjectMapper().readValue(data, FullyTypedThing.class) - if you want to read an array, just pass in an array of that class to the same method, as in: new ObjectMapper().readValue(data, FullyTypedThing[].class – NS du Toit Jun 2 '16 at 19:42

Jackson API, use the Jackson API for binding JSON data to Plain Old Java Object Jackson API to serialize and deserialize the java collection objects such as List, Map etc. INDENT_OUTPUT); List<String> books = new ArrayList<>();  Deserializing into a HashMap of custom objects with jackson. How to use Jackson to deserialise an array of objects ignoring unknown fields on JSON objects

Java and JSON – Jackson Serialization with ObjectMapper, A complete set of examples for serialization and deserialization with A list of String objects gets serialized by default as a simple JSON array. How to deserialize JSON file starting with an array in Jackson? of com.project.my.Objects out of START_ARRAY token to use Jackson to deserialise an array of

Comments
  • I prefer Google's GSON library for dealing with JSON. It is worth checking out if you haven't tryed it yet... makes working with it very easy and intuitive.
  • FWIW The possible solutions to this specific problem with Gson are almost identical to what's possible with Jackson's Data Binding API.
  • Gweebz -- maybe you would like to explain why you feel GSON is a better choice (compared to Jackson)?
  • One extra note, if while parsing you get an error such as JsonMappingException: No suitable constructor found for type then it means you need to added a default constructor to your class adding a private no-arg constructor fixed it for me.
  • @SyntaxRules adding explicit constructor is necessary if you have an explicit constructor -- if not, compiler automatically creates public "empty" constructor. Good point. Another common problem is that inner classes need to be static -- otherwise they never have zero-arg constructor.
  • Btw, List<MyClass> myObjects = Arrays.asList(mapper.readValue(json, MyClass[].class)) works up to 10 time faster than TypeRefence.
  • I'm looking for a generic type version.
  • @EugeneTskhovrebov your way is the cleanest for inlining. The others require casting or declaring. I suggest adding it as its own answer to help highlight it, and give you some rep.
  • For those working with Agents in Java, Lotus Domino, this is the way to go. I tried some of the other solutions, but always got a ResourceNotFoundException
  • SyntaxRules addition in the comments for the answer above may be required for this solution as we, it was for me. I just wanted to add that so that it is not lost.
  • or Arrays.asList(Json.fromJson(json.get("fieldName"), MyClass[].class))
  • or List<MyClass> myObjects = Arrays.asList(mapper.treeToValue(jsonNode.get("fieldName"), MyClass[].class))
  • @CollinKrawll what does objectmapper.treetovalue do?
  • Nice construct of Class<T[]>. Never saw this. Where did you find information about this?
  • This is exactly what I'm looking for, thanks