Jackson && Lombok

Thu, Feb 4, 2021 4-minute read

Lombok

@Data

@Data
public class UserBean{
  private Integer id;
  private String userName;
}

@Getter @Setter @RequiredArgsConstructor @ToString @EqualsAndHashCode

@Getter/@Setter

@NonNull

public String getName(@NonNull Person p) {
    return p.getName();
}


public String getName(@NonNull Person p) {
    if (p == null) {
        throw new NullPointerException("p");
    }
    return p.getName();
}

@ToString/@EqualsAndHashCode

@ToString(exclude={“param1”，“param2”})

@ToString(of={“param1”，“param2”})

@NoArgsConstructor/@RequiredArgsConstructor /@AllArgsConstructor

@NoArgsConstructor
@RequiredArgsConstructor(access = AccessLevel.PROTECTED)
@AllArgsConstructor
public class Shape {
    private int x;

    @NonNull
    private int y;

    @NonNull
    private String name;
}

equals


public class Shape {
    private int x;

    @NonNull
    private int y;

    @NonNull
    private String name;
}

public Shape(){}
    
protected Shape(int x,@NonNull double y,String name){
        this.x = x;
        this.y = y;
        this.name = name;
    }


    public Shape (double y,String name){
        return new Shape(y,name);
    }

@Slf4j

use Slf4j in lombok, you don’t code below to test.

private final Logger logger = LoggerFactory.getLogger(XXX.class)

log.info(“xxxx{}”, key);

@Builder

public class User {
    private String name;
    private String password;

    public void setName(String name) {
        this.name = name;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}


User user = new User();
user.setName("aa");
user.setPassword("1111");

now compared to Immutable Objects

public class User {
    private final String name;
    private final String password;

    public User(String name, String password) {
        this.name = name;
        this.password = password;
    }
}

need more than more constructor

public class UserBuilder {
    private String name;
    private String password;

    public UserBuilder name(String name) {
        this.name = name;
        return this;
    }

    public UserBuilder password(String password) {
        this.password = password;
        return this;
    }

    public User build() {
        return new User(name, password);
    }

     public static UserBuilder User() {
        return new UserBuilder();
    }
}


User user = UserBuilder.user()
                .name("milo")
                .password("123456")
                .build();

lombok has tight coupling issues

@RequiredArgsConstructor
@RestController
public class MyController {
  private final RoleAccessService roleAccessService;
  private final QueueService queueService;
  private final ManagementService managementService;
  private final SecurityConfig securityConfig;
  private final JsonAdapter jsonAdapter;
  
  // REST methods
}

equals

@RestController
public class MyController {
  private final RoleAccessService roleAccessService;
  private final QueueService queueService;
  private final ManagementService managementService;
  private final SecurityConfig securityConfig;
  private final JsonAdapter jsonAdapter;
  
  @Autowired
  public MyController(RoleAccessService roleAccessService,
                      QueueService queueService,
                      ManagementService managementService,
                      SecurityConfig securityConfig,
                      JsonAdapter jsonAdapter) {
    this.roleAccessService = roleAccessService;
    this.queueService = queueService;
    this.managementService = managementService;
    this.securityConfig = securityConfig;
    this.jsonAdapter = jsonAdapter;
  }
  
  // REST methods
}

The lombok would make you forget your class becoming too big or it has two much responsibility

always remember to watch out the dependencies

JackSon

jackson-databind in

ObjectMapper

The simple readValue API of the ObjectMapper is a good entry point. We can use it to parse or deserialize JSON content into a Java object.

use the writeValue API to serialize any Java object as JSON output.

Java Object to JSON

ObjectMapper objectMapper = new ObjectMapper();
Person p = new Person("15", "female"); // private String age; private String sex;
objectMapper.writeValue(new File("target/p.json"), p); // {"age": "15", sex": "female"}

JSON to Java Object

String json = "{\"age"\" : \"15"\", \"sex"\" : \"female"\"}";
Person p = objectMapper.writeValue(json, Person.class);
Person p = objectMapper.writeValue(new URL("file:src/java/exe/json_p.json"),  Person.class);

JSON to Object, List, Map

public class User {
    private int id;
    private String name;
    // get, set
}

public class Client {
    public static void main(String[] args) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();

        // User Object to json
        User user1 = new User(1, "AA");
        String json = objectMapper.writeValueAsString(user1);

         //  json to  User Object
        User user1 = new User(1, "AA");
        User user2 = objectMapper.readValue(json, User.class);

         //  List<User> to  json
        List<User> uli = new ArrayList<>();
         User user3 = new User(2, "BB");
         uli.add(user3);
         String ujson = objectMapper.writeValueAsString(uli);

         //  json to  List<User>
       List<User> ulist = objectMapper.readValue(json, new TypeReference<List<User>>() {});

         //  Map<Strng, User> to  json
         HashMap<String, User> umap = new HashMap<>();
        User user4 = new User(4, "CC");
        umap.put("CC", user4);
        String mjson2 = objectMapper.writeValueAsString(umap);

         //  json to  Map<Strng, User>
           Map<Strng, User>  umap1 = objectMapper.readValue(json, new TypeReference<HashMap<String, User>>() {});

    }

public class Game<T> {
    private Integer id;
    private T source;
}


public class Item {
    private String color;
    private Integer price;
}

json

{
    "id":001,
    "source": {
        "color" : "white",
        "price" : 20
    }
}

// json to class

public class Client {
    public static <T> Game<T> convert(String json, Class<T> targetClass) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();

        Game<T> game = null; 

        JavaType clazzType = objectMapper.getTypeFactory().constructParametricType(Game.class, targetClass);

        game =  objectMapper.readValue(json, clazzType);

        return game;
    }

    public static void main(String[] args) {
        String json = "{\"id\": 001,\"source\": {\"color\": \"white\",\"price\": 20}}";

        Game<Item> game1 = convert(json, Item.class);
    }
}

Jackson2