deserialize a json array into a java object holding list

Question

I'm getting a json array holding objects looking like this:

[
    {
        "id": "1",
        "name": "some name",
        "url": "some url",
        "active": true
    }, {
        "id": "2",
        "name": "some other name",
        "url": "some other url",
        "active": true
    }
]

Now, I want to be able to deserialize that array into a java object holding a list of the objects in the array. I have made a custom deserializer looking like this:

public class ListSerializer extends JsonDeserializer<List<Provider>>{

    private static final long serialVersionUID = 9114152571639338391L;

    @Override
    public List<Provider> deserialize(JsonParser jsonParser, 
    DeserializationContext arg1) throws IOException, JsonProcessingException {
    // TODO Auto-generated method stub
    final ObjectCodec objectCodec = jsonParser.getCodec();
    final JsonNode listOrObjectNode = objectCodec.readTree(jsonParser);
    final List<Provider> result = new ArrayList<Provider>();
    for (JsonNode node : listOrObjectNode) {
      result.add(objectCodec.treeToValue(node, Provider.class));
    }
      return result;
    }
}

And the class holding the list looks like this:

public class ProviderList {

    @JsonDeserialize(using = ListSerializer.class)
    private List<Provider> providerList;

     public List<Provider> getProviderList() {
      return providerList;
    }

    public void setProviderList(final List<Provider> providerList) {
      this.providerList = providerList;
     }
}

I am obviously doing something wrong, because I'm getting this error:

Can not deserialize instance of com.wirelesscar.trailser.v1_0.domain.ProviderList out of START_ARRAY token at [Source: [{"id":"1","name":"Posttrack","url":"http:\dev.posttrack.com","active":true},{"id":"2","name":"Trackunit","url":"http:\dev.trackunit.com","active":true}]; line: 1, column: 1]

How can I do this properly?

score 3 · Accepted Answer · answered May 04 '17 at 10:09

You can deserialize directly to a list by using the TypeReference wrapper.

@Data
public class Provider {
    private Long id;
    private String name;
    private String url;
    private boolean active;
}

@Data
public class ProviderList {
    List<Provider> providerList;
}

public class JsonTest {

    @Test
    public void  test() {
        String json = "[{\n" +
                "        \"id\": \"1\",\n" +
                "        \"name\": \"some name\",\n" +
                "        \"url\": \"some url\",\n" +
                "        \"active\": true\n" +
                "    }, {\n" +
                "        \"id\": \"2\",\n" +
                "        \"name\": \"some other name\",\n" +
                "        \"url\": \"some other url\",\n" +
                "        \"active\": true\n" +
                "    }\n" +
                "]";

        ObjectMapper mapper = new ObjectMapper();
        try {
            List<Provider> providerList = mapper.readValue(json, new TypeReference<List<Provider>>(){});
            for (Provider provider : providerList) {
                System.out.println(provider);
            }

            ProviderList list = new ProviderList();
            list.setProviderList(providerList);

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

deserialize a json array into a java object holding list

1 Answers1