ObjectMapper objectMapper = new ObjectMapper();
String carJson ="{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
Car car = objectMapper.readValue(carJson, Car.class);

ObjectMapper objectMapper = new ObjectMapper();
String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 4 }";
Reader reader = new StringReader(carJson);
Car car = objectMapper.readValue(reader, Car.class);

ObjectMapper objectMapper = new ObjectMapper();
File file = new File("data/car.json");
Car car = objectMapper.readValue(file, Car.class);

ObjectMapper objectMapper = new ObjectMapper();
URL url = new URL("file:data/car.json");
Car car = objectMapper.readValue(url, Car.class);

String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
ObjectMapper objectMapper = new ObjectMapper();
Car[] cars2 = objectMapper.readValue(jsonArray, Car[].class);

ObjectMapper objectMapper = new ObjectMapper();
String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
byte[] bytes = carJson.getBytes("UTF-8");
Car car = objectMapper.readValue(bytes, Car.class);

String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
ObjectMapper objectMapper = new ObjectMapper();
Car[] cars2 = objectMapper.readValue(jsonArray, Car[].class);

String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
ObjectMapper objectMapper = new ObjectMapper();
List<Car> cars1 = objectMapper.readValue(jsonArray, new TypeReference<List<Car>>(){});

String jsonObject = "{\"brand\":\"ford\", \"doors\":5}";
ObjectMapper objectMapper = new ObjectMapper();
Map<String, Object> jsonMap = objectMapper.readValue(jsonObject,new TypeReference<Map<String,Object>>(){});

  ObjectMapper objectMapper = new ObjectMapper();
  Car car = new Car();
  car.setBrand("宝马");
  car.setDoors(4);
  String json = objectMapper.writeValueAsString(car);
  System.out.println(json);

  Transaction transaction = new Transaction("transfer", new Date());
  ObjectMapper objectMapper = new ObjectMapper();
  SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
  objectMapper.setDateFormat(dateFormat);
  String output2 = objectMapper.writeValueAsString(transaction);
  System.out.println(output2);

  String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
  ObjectMapper objectMapper = new ObjectMapper();
  try {
      JsonNode jsonNode = objectMapper.readValue(carJson, JsonNode.class);
      //使用ObjectMapper readTree()方法将JSON解析为JsonNode
      JsonNode jsonNode = objectMapper.readTree(carJson);
  } catch (IOException e) {
      e.printStackTrace();
  }

ObjectMapper objectMapper = new ObjectMapper();
Car car = new Car();
car.brand = "Cadillac";
car.doors = 4;
JsonNode carJsonNode = objectMapper.valueToTree(car);

ObjectMapper objectMapper = new ObjectMapper();
String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
JsonNode carJsonNode = objectMapper.readTree(carJson);
Car car = objectMapper.treeToValue(carJsonNode);

无论是单个元素，数组还是对象，都可以用get来获取
String carJson =
        "{ \"brand\" : \"Mercedes\", \"doors\" : 5," +
        "  \"owners\" : [\"John\", \"Jack\", \"Jill\"]," +
        "  \"nestedObject\" : { \"field\" : \"value\" } }";

ObjectMapper objectMapper = new ObjectMapper();
try {
    JsonNode jsonNode = objectMapper.readValue(carJson, JsonNode.class);
    //获取字符串类型单个元素
    JsonNode brandNode = jsonNode.get("brand");
    String brand = brandNode.asText();
    System.out.println("brand = " + brand);
    //获取Int类型单个元素
    JsonNode doorsNode = jsonNode.get("doors");
    int doors = doorsNode.asInt();
    System.out.println("doors = " + doors);
    //获取数组类型的元素
    JsonNode array = jsonNode.get("owners");
    JsonNode jsonNode = array.get(0);
    String john = jsonNode.asText();
    System.out.println("john  = " + john);
    //获取嵌套对象的数据
    JsonNode child = jsonNode.get("nestedObject");
    JsonNode childField = child.get("field");
    String field = childField.asText();
    System.out.println("field = " + field);
    //获取子路径下的数据 如果没有匹配到则返回null
    JsonNode nameNode = jsonNode.at("/nestedObject/field");
} catch (IOException e) {
    e.printStackTrace();
}

String f2Str = jsonNode.get("f2").asText();
double f2Dbl = jsonNode.get("f2").asDouble();
int    f2Int = jsonNode.get("f2").asInt();
long   f2Lng = jsonNode.get("f2").asLong();

如果找到对应字段，但是字段的值为null，可设置返回默认值。
不适应于没有找到字段的情况，因为这样get()方法会直接返回null，asText无法进行调用。
ObjectMapper objectMapper = new ObjectMapper();
String json = "{ \"f1\":\"Hello\", \"f2\":null }";
JsonNode jsonNode = objectMapper.readTree(json);
String f2Value = jsonNode.get("f2").asText("Default");

ObjectNode属于JsonNode的子类，所以JsonNode的功能，ObjectNode都可以使用。
创建一个ObjectNode
ObjectMapper objectMapper = new ObjectMapper();
ObjectNode objectNode = objectMapper.createObjectNode();
Set设置字段
将名称String和JsonNode作为参数传递，下面是Jackson的ObjectNode上设置字段的示例。
parentNode.set("child1", JsonNode);
parentNode.set("child1", ObjectNode);
Put设置字段
直接设置String类型的字段数据
objectNode.put("field1", "value1");
PutArray设置数组
ArrayNode nodes = objectNode.putArray("sonArray");
nodes.add(JsonNode);
nodes.add(ObjectNode);
删除字段
objectNode.remove("fieldName");
JsonObject转ObjectNode
ObjectNode jsonNodes = jsonNode.deepCopy();

ObjectMapper objectMapper = new ObjectMapper();
//忽略位置的JSON字段
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//不允许基本类型为null
objectMapper.configure(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES, true);
//时间类型数据转换
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
objectMapper.setDateFormat(dateFormat);