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jackson

reference

  • https://chatgpt.com/c/0f8b8a16-cab5-4fbb-8f0e-1c7949dd97f4 - anno 1
  • https://chatgpt.com/c/cbe3f6c3-c238-4db8-99e5-a0c9c9ddffec - anno 2
  • https://chatgpt.com/c/4334405c-e8c0-4e88-a138-a53b14ae52b5 - object mapper
  • https://www.baeldung.com/jackson
  • Json , JsonStr , Object , JsonNode(asText(), readTree())
  • Objectmapper / Xmlmapper API
  • @ResquestBody and @responseBody behind the scene perform S and D using OM.
  • Advance Section pending : https://www.baeldung.com/jackson

Common task

  1. Serialize and Deserialize
  2. Class, generic-Class
  3. interface and abstractClass : Does not work.
  4. property order, alias, root
  5. Type/property
  6. @JsonAlias
  7. @JsonUnwrapped - performs flattening. {a,{b,c}} === {a,b,c}
  8. @JsonSetter is an alternative to @JsonProperty that marks the method as a setter method.
  9. @JsonIgnore, @JsonIgnoreType, @JsonFilter - conditionally ignore.
  10. @JsonInclude(Include.NOT_NULL) , @JsonIncludeProperties class
  11. globally set : om.setSerializationInclusion(Include.NON_NULL);
  12. formatting : date, time, number, etc :
  13. @DateTimeFormat(fromSB)
  14. om.setDateFormat(new SimpleDateFormat(" "))
  15. handle collection.
  16. @JsonCreator(apply on constructor/method to create/return object) tune the constructor/factory used in deserialization.

    - String jsonCarArray ="[{ \"color\" : \"Black\", \"type\" : \"BMW\" }, { \"color\" : \"Red\", \"type\" : \"FIAT\" }]";
      List<Car> listCar = objectMapper.readValue(jsonCarArray, new TypeReference<List<Car>>(){});

    - String json = "{ \"color\" : \"Black\", \"type\" : \"BMW\" }";
      Map<String, Object> map = objectMapper.readValue(json, new TypeReference<Map<String,Object>>(){});
5. handle raw json 6. handle Enums - @JsonValue for S, @JsonCreator for D ``` // Default public enum Status {SUCCESS,FAILURE,PENDING} String json = mapper.writeValueAsString(Status.SUCCESS); // "\"SUCCESS\"" Status status = mapper.readValue(json, Status.class); // SUCCESS

// @JsonValue for S, @JsonCreator for D public enum Status {String v;SUCCESS("S"),FAILURE("F"),PENDING("P"); Status(string v){} @JsonValue getValue(v) @JsonCreator m(v){...} } String json = mapper.writeValueAsString(Status.SUCCESS); // "\"S\"" Status status = mapper.readValue(json, Status.class); // S 7. Don't use Optional<T> as json property. - Add Dependencies : jackson-datatype-jdk8. - objectMapper.registerModule(new Jdk8Module()); - @JsonInclude(JsonInclude.Include.NON_ABSENT) // Optional fields are included if present public class Event { private String name; private Optional description; } ``` 8. handle visibilty: @JsonAutoDetect(fieldVisibility = Visibility.ANY) // Private feild. etc. 9.

Advance task

  1. inject
    • @JacksonInject indicates that a property will get its value from the injection and not from the JSON data. 
         InjectableValues inject = new InjectableValues.Std().addValue(int.class, 1);
   BeanWithInject bean = new ObjectMapper()
                         .reader(inject)
                         .forType(BeanWithInject.class)
                         .readValue(json);
      2.

Objectmapper

  • Builder pattern

Serialize

  • writeValue(obj) or
  • writeValueAsString(obj)
  • Apply Filter :
  • @JsonFilter("Filter-1") class
  • om.writer(SimpleFilterProvider p).writeValue(obj) //p.addFilter("Filter-1", filterObject eg:SimpleBeanPropertyFilter)

De-serialize

  • readvalue (json, TypeReference)
  • readerFor(T).readValue(obj)

Config

  • unknown/incomplete

    • FAIL_ON_UNKNOWN_PROPERTIES , @JsonIgnoreProperties(ignoreUnknown = true) MyClass
    • FAIL_ON_NULL_FOR_PRIMITIVES : unmarshalling an incomplete JSON : @JsonProperty(required = false.True)

  • mapper.enable(DeserializationFeature.UNWRAP_ROOT_VALUE);

  • WRITE_DATES_AS_TIMESTAMPS,
  • DEFAULT_VIEW_INCLUSION,
  • INDENT_OUTPUT
  • OM >> register module >> add custom S and D
  • OM.configure(k,v)
  • on DTO >> Apply annotation
  • https://chatgpt.com/c/0f8b8a16-cab5-4fbb-8f0e-1c7949dd97f4
  • https://chatgpt.com/c/cbe3f6c3-c238-4db8-99e5-a0c9c9ddffec
  • spring.jackson..=true,false
    • spring.jackson.serialization.indent_output=true
    • spring.jackson.deserialization.fail-on-unknown-properties=false
    • spring.jackson.mapper.auto-detect-fields=true // @JsonAutoDetect
    • spring.jackson.parser.allow-comments=true
    • spring.jackson.generator.escape-non-ascii=true 
            return new ObjectMapper()
          .enable(SerializationFeature.INDENT_OUTPUT)             // Enable pretty printing
          .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES) // Ignore unknown properties
          .enable(MapperFeature.AUTO_DETECT_FIELDS)              // Auto-detect fields
          .enable(JsonParser.Feature.ALLOW_COMMENTS)             // Allow comments in JSON
          .enable(JsonGenerator.Feature.ESCAPE_NON_ASCII);
  • UnrecognizedPropertyException : objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
  • extends Std/JsonSerializer --> serialize(T object, JsonGenerator jsonGenerator, SerializerProvider serializer) {...}
  • extends Std/JsonDeserializer --> T deserialize(JsonParser parser, DeserializationContext deserializer) {...}
  • @JsonCreator : Apply on contructor (@jsonproperty on arg). that constructor is used while unmarshalling
  • @JsonDeserialize(as = Cat.class) Animal a ; // Animal is Interface.
  • @JsonFormat : specifies a format when serializing Date/Time values
  • usally used for java,util.Date, Double price (patter="#0.00")
  • @JsonFormat(shape = JsonFormat.Shape.String, pattern="") Date //
  • @JsonFormat(shape = JsonFormat.Shape.NUMBER) Date //Timeinmilliseconds
  • @JsonFormat(with = JsonFormat.Feature.ACCEPT_CASE_INSENSITIVE_PROPERTIES) class // IMP