Jackson Json Basic

Written By David Roh, VCANUS

Jackson Json Basic

Basic Structure

• JsonNode
  • read only
  • includes object json, array json, value json
• ObjectNode
  • {}
  • object json
  • read / write
• ArrayNode
  • []
  • array json
  • read / write
• ValueNode
  • value
  • string, boolean, number ..

Common Using Object

• ObjectMapper

ObjectMapper jsonMapper = new ObjectMapper();

Create Json Object

Empty json

• using mapper

ObjectNode objectJson = jsonMapper.createObjectNode();
ArrayNode arrayJson = jsonMapper.createArrayNode;

• using JsonNodeFactory

JsonNodeFactory.instance.objectNode();
JsonNodeFactory.instance.arrayNode();

From Json String to Jackson Object

JsonNode jsonNode = jsonMapper.readTree(jsonString);

if(jsonNode.isObject()) {
    ObjectNode json = (ObjectNode)jsonNode;
}

if(jsonNode.isArray()) {
    ArrayNode json = (ArrayNode)jsonNode;
}

From Java Collection to Jackson Object

// List list - array type
JsonNode jsonNode = jsonMapper.convertValue(list, JsonNode.class);
ArrayNode arrayNode = jsonMapper.convertValue(list, JsonNode.class);

// Map map - object type
JsonNode jsonNode = jsonMapper.convertValue(map, JsonNode.class);
ObjectNode objectNode = jsonMapper.convertValue(map, JsonNode.class);

Convert JsonNode to POJO

From Jackson Object to JavaCollection

// array type
List list = jsonMapper.convertValue(jsonNode /* or arrayNode */, ArrayList.class);

// object type
Map map = jsonMapper.convertValue(jsonNode /* or objectNode */, HashMap.class);
Map map = jsonMapper.convertValue(jsonNode /* or objectNode */, LinkedHashMap.class);

From Jackson Object to Json String

jsonNode.toString();

From Json String to Java Collection

// array type
List list = jsonMapper.readValue(jsonString, List.class);

// object type
Map map = jsonMapper.readValue(jsonString, Map.class);

GET, SET Value

Get Value From Jackson Object

• check key

// object type
boolean re = jsonNode.has(key);

// array type
boolean re = jsonNode.has(index);

• Get JsonNode

// object type
JsonNode targetNode = jsonNode.get(key/*index*/);
    
// array type
JsonNode targetNode = jsonNode.get(index);

• Get Value When JsonNode is ValueNode

as[DataType](/*default value*/) 함수 : 지정된 DataType으로 casting하여 return
casting이 안될경우에 대비하여 default값 지정 가능
ex) targetNode.asInt(123)

asText(defaultValue)의 경우 값이 null인 경우만 작동
targetNode가 ArrayNode이거나 ObjectNode인 경우는 공백을 리턴
ex) targetNode.asText()

[dataType]Value() 함수 : 해당 type경우에 값을 return
해당하지 않으면 null을 리턴
ex) targetNode.textValue()

toString() 함수 : json string으로 출력

boolean : true / false
number : 1, 1.123
string : "string"

ex) targetNode.toString()

Set Value To Jackson Object

• Set to ObjectNode

// set valueNode
objectNode.put(key, value);

// set jsonNode(objectNode, arrayNode)
objectNode.set(key, jsonNode);

• Set to ArrayNode

// set valueNode
arrayNode.add(value);

// set jsonNode(objectNode, arrayNode)
arrayNode.add(jsonNode);