JSON to java object

JSON is a data format that works well with JavaScript applications and has become the default choice while working with REST Data Services. In this example we will show how to convert a json to a java object using GSON and jackson, two popular open source libraries. In addition we will show how to convert json to an arraylist and array.

In the set up method we will create a java object called Plane and create constants that will be used when validating each library conversation from java to json.

Setup

static class Plane {
    private String planeType;

    public Plane() {
    }
    
    public String getPlaneType() {
        return planeType;
    }
    
    @Override
    public String toString() {
        return Objects.toStringHelper(this).add("plane type: ", planeType).toString();
    }
    
}

private final String ARRAY_AS_JSON = "[{\"planeType\":\"Commercial Transport Planes\"},{\"planeType\":\"General Aviation Planes\"},{\"planeType\":\"Military Planes\"},{\"planeType\":\"Sea Planes\"},{\"planeType\":\"Special Purpose Planes\"}]";

private static final String JSON_OBJECT = "{\"planeType\":\"Sea Planes\"}";

GSON

JSON to object

@Test
public void unmarshall_json_to_object_with_gson () {
    Gson gson = new Gson();

    Plane plane = gson.fromJson(JSON_OBJECT, Plane.class);

    logger.info(plane);
    
    assertEquals("Sea Planes", plane.getPlaneType());
}

Output

Plane{plane type: =Sea Planes}

JSON to list

@Test
public void unmarshall_json_to_list_with_gson () {
    
    Gson gson = new Gson();
    
    @SuppressWarnings("serial")
    List<Plane> planes = gson.fromJson(ARRAY_AS_JSON, new TypeToken<List<Plane>>(){}.getType());
    
    logger.info(planes);
    
    assertEquals(5, planes.size());
}

Output

[
    Plane{plane type: =Commercial Transport Planes}, 
    Plane{plane type: =General Aviation Planes}, 
    Plane{plane type: =Military Planes}, 
    Plane{plane type: =Sea Planes}, 
    Plane{plane type: =Special Purpose Planes}
]

JSON to array

@Test
public void unmarshall_json_to_java_array_with_gson () {
    
    Gson gson = new Gson();
    
    Plane[] planes = gson.fromJson(ARRAY_AS_JSON, Plane[].class);
    
    logger.info(planes);
    
    assertEquals(5, planes.length);
}

Output

[
    Plane{plane type: =Commercial Transport Planes}, 
    Plane{plane type: =General Aviation Planes}, 
    Plane{plane type: =Military Planes}, 
    Plane{plane type: =Sea Planes}, 
    Plane{plane type: =Special Purpose Planes}
]

Jackson

JSON to object

@Test
public void unmarshall_json_to_object_with_jackson () throws JsonParseException, JsonMappingException, IOException {
    ObjectMapper objectMapper = new ObjectMapper();
    
    Plane plane = objectMapper.readValue(JSON_OBJECT, Plane.class);
    
    logger.info(plane);

    assertEquals("Sea Planes", plane.getPlaneType());
}

Output

Plane{plane type: =Sea Planes}

JSON to list

@Test
public void unmarshall_json_to_list_with_jackson () throws JsonParseException, JsonMappingException, IOException {
    
    ObjectMapper objectMapper = new ObjectMapper();
    
    List<Plane> planes = objectMapper.readValue(ARRAY_AS_JSON, 
            objectMapper.getTypeFactory().constructCollectionType(List.class, Plane.class));
    
    logger.info(planes);

    assertEquals(5, planes.size());
}

Output

[
    Plane{plane type: =Commercial Transport Planes}, 
    Plane{plane type: =General Aviation Planes}, 
    Plane{plane type: =Military Planes}, 
    Plane{plane type: =Sea Planes}, 
    Plane{plane type: =Special Purpose Planes}
]

JSON to array

@Test
public void unmarshall_json_to_java_array_with_jackson () throws JsonParseException, JsonMappingException, IOException {
    
    ObjectMapper objectMapper = new ObjectMapper();
    
    Plane[] planes = objectMapper.readValue(ARRAY_AS_JSON, JsontoJavaObject.Plane[].class);
    
    logger.info(Arrays.toString(planes));

    assertEquals(5, planes.length);
}

Output

[
    Plane{plane type: =Commercial Transport Planes}, 
    Plane{plane type: =General Aviation Planes}, 
    Plane{plane type: =Military Planes}, 
    Plane{plane type: =Sea Planes}, 
    Plane{plane type: =Special Purpose Planes}
]