Map an array of JSON objects to a java.util.Map and vice versa

How to deserialize a JSON string

You can use Jackson to deserialize a JSON string:

For example if you have class Foo

public class Foo {   private Bar[] items;   // Constructor / Getters & Setters} 

And that class has an array of class Bar

 public class Bar {     private int field1;     private String field2;     // Constructor / Getters & Setters }

Where the field names match those in your JSON string then you can do the following to convert it:

String jsonString = "{\"items\": [{\"field1\": 1, \"field2\": \"Hello\"}, {\"field1\": 2, \"field2\":\"World\"}]}";ObjectMapper mapper = new ObjectMapper();Foo foo = mapper.readValue(jsonString, Foo.class);

If you are using Maven, the following dependency would be required in your pom.xml:

    <dependency>        <groupId>com.fasterxml.jackson.core</groupId>        <artifactId>jackson-databind</artifactId>        <version>${jackson.version}</version>    </dependency>

Approaches to solve your problem:

Option 1 - Custom Deserializer

Write a custom JsonDeserializer to deserialize your JSON string into a Storage object with a field items of type Map<String,Item>

 public class CustomDeserializer extends JsonDeserializer<Storage> {    @Override    public Storage deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)            throws IOException {        Map<Integer, Item> map = new HashMap<>();        ObjectCodec oc = jsonParser.getCodec();        JsonNode rootNode = oc.readTree(jsonParser);        JsonNode items = rootNode.get("items");        for (int i = 0; i < items.size(); i++) {            JsonNode childNode = items.get(i);            Item item = new Item(childNode.get("field1").asInt(), childNode.get("field2").asText());            map.put(item.getField1(), item);        }        return new Storage(map);    }}

You would then annotate your Storage class with the following:

@JsonDeserialize(using = CustomDeserializer.class)

Your Storage class would look something like;

@JsonDeserialize(using = CustomDeserializer.class)public class Storage {   private Map<Integer, Item> items;   public Storage(Map<Integer, Item> map) {    this.items = map;   }   ...}

Option 2 - Create Map post deserialization

Deserialize the JSON string into a Storage object with an array of Item as described at the beginning and then construct your Map<Integer, Item> after.

Hope this helps.

You can create your own custom Serializers/Deserializers to achieve this. Jackson provides a neat way of doing this. Just annotate the Storage class with @JsonDeserialize(using = YourDeserializer.class) and have the logic to convert the json in YourDeserializer.

The array of JSON objects is an array of Items, right? So why not simply deserialize the array into a Java array of Items and then build the Map from there?