Jacksonの統合とベストプラクティス

  com.fasterxml.jackson.core
  jackson-core
  2.8.6


  com.fasterxml.jackson.core
  jackson-databind
  2.7.0


  com.fasterxml.jackson.core
  jackson-annotations
  2.8.6

ObjectMapper mapper = new ObjectMapper(); // create once, reuse
//    ：
MyValue value = mapper.readValue(new File("data.json"), MyValue.class);
// or:
value = mapper.readValue(new URL("http://some.com/api/entry.json"), MyValue.class);
// or:
value = mapper.readValue("{\"name\":\"Bob\", \"age\":13}", MyValue.class);

//   ：
mapper.writeValue(new File("result.json"), myResultObject);
// or:
byte[] jsonBytes = mapper.writeValueAsBytes(myResultObject);
// or:
String jsonString = mapper.writeValueAsString(myResultObject);

//   
Map scoreByName = mapper.readValue(jsonSource, Map.class);
List names = mapper.readValue(jsonSource, List.class);
//     
Map results = mapper.readValue(jsonSource, new TypeReference

// map ObjectNode，list ArrayNode，     JsonNode
// map   :
// set("string",variable);
// put("string",string/int);
// get("string");
// list   :
// add("string"/variable);

// mapper.readTree(String) String   ，   JsonNode
// mapper.writeValueAsString(JsonNode)  JsonNode     
// mapper.writeTree(JsonGenerator, JsonNode)  JsonNode     。     JsonFactory.createGenerator()  ，   Writer, File, OutputStream 。
// can be read as generic JsonNode, if it can be Object or Array; or,
// if known to be Object, as ObjectNode, if array, ArrayNode etc:
ObjectNode root = mapper.readTree("stuff.json");
String name = root.get("name").asText();
int age = root.get("age").asInt();

// can modify as well: this adds child Object as property 'other', set property 'type'
root.with("other").put("type", "student");
String json = mapper.writeValueAsString(root);

// with above, we end up with something like as 'json' String:
// {
//   "name" : "Bob", "age" : 13,
//   "other" : {
//      "type" : "student"
//   }
// }

     ，    。      。

// to allow serialization of "empty" POJOs (no properties to serialize)
// (without this setting, an exception is thrown in those cases)（         ）
mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
// to write java.util.Date, Calendar as number (timestamp):（       ）
mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
// to allow (non-standard) unquoted field names in JSON:（        ，  FastJson   bug）
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
// to allow use of apostrophes (single quotes), non standard（   ）
mapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);