This document provides an overview of Lombok, a Java library that automatically plugs into editors and builds to provide automatic generation of boilerplate code like getters, setters, equals, hashCode and toString methods. It summarizes the main Lombok annotations like @Getter, @Setter, @ToString, @EqualsAndHashCode, @Builder and how they generate standard Java code. It also covers other annotations like @Value, @Data, @Slf4j, @NonNull, @Cleanup and how they simplify code. In the end it provides links to learn more about Lombok features and the delombok tool.

1. Lombok
2017-07-20
onozaty

2. Lombok?
• Java (
)
•
• getter/setter
• equals, hashCode
• toString
•

3. Lombok?
•
@Getter
@Setter
public class Customer {
private int id;
private String name;
}
public class Customer {
private int id;
private String name;
public int getId() {
return this.id;
}
public String getName() {
return this.name;
}
public void setId(final int id) {
this.id = id;
}
public void setName(final String name) {
this.name = name;
}
}

4. Lombok?
• IDE IDE

5. • Lombok
( )
• IDE
• Eclipse Lombok jar
Eclipse
( )

6. @Getter, @Setter
• getter/setter
• (
)
• (
public)
• final setter (
)

7. @Getter, @Setter
public class GetterSetterExample {
//
@Getter
@Setter
private int id;
//
@Setter(AccessLevel.PROTECTED)
private String name;
}
public class GetterSetterExample {
private int id;
private String name;
public int getId() {
return this.id;
}
public void setId(final int id) {
this.id = id;
}
protected void setName(final String name) {
this.name = name;
}
}

8. @ToString
•
toString
•

9. @ToString
@ToString
public class ToStringExample {
private int id;
private String name;
public String getName() {
return name;
}
}
// exclude
@ToString(exclude = "name")
class ToStringExample2 {
private int id;
private String name;
}
public class ToStringExample {
private int id;
private String name;
public String getName() {
return name;
}
@Override
public String toString() {
return "ToStringExample(id=" + this.id
+ ", name=" + this.getName() + ")";
}
}
class ToStringExample2 {
private int id;
private String name;
@Override
public String toString() {
return "ToStringExample2(id="
+ this.id + ")";
}
}

10. @EqualsAndHashCode
• equals hashCode
•
•
Lombok

11. @EqualsAndHashCode
@EqualsAndHashCode
public class EqualsAndHashCodeExample
{
private int id;
private String name;
}
//
@EqualsAndHashCode(exclude = "age")
class EqualsAndHashCodeExample2 {
private int id;
private String name;
private int age;
}
public class EqualsAndHashCodeExample {
private int id;
private String name;
@Override
public boolean equals(final Object o) { … }
@Override
public int hashCode() { … }
}
public class EqualsAndHashCodeExample2 {
private int id;
private String name;
private int age;
// age
@Override
public boolean equals(final Object o) { … }
@Override
public int hashCode() { … }
}

12. @AllArgsConstructor,
@NoArgsConstructor,
@RequiredArgsConstructor
•
• @AllArgsConstructor
• @NoArgsConstructor
• @RequiredArgsConstructor final
(final
)

13. @AllArgsConstructor,
@NoArgsConstructor,
@RequiredArgsConstructor
@AllArgsConstructor
@NoArgsConstructor
public class ConstructorExample {
private int id;
private String name;
}
@RequiredArgsConstructor
class ConstructorExample2 {
private final int id;
private String name;
}
public class ConstructorExample {
private int id;
private String name;
public ConstructorExample(
final int id, final String name) {
this.id = id;
this.name = name;
}
public ConstructorExample() {
}
}
class ConstructorExample2 {
private final int id;
private String name;
public ConstructorExample2(final int id) {
this.id = id;
}
}

14. @Data
•
• @ToString
• @EqualsAndHashCode
• @Getter
• @Setter
• @RequiredArgsConstructor
•

15. @Data
@Data
public class DataExample {
private final int id;
private String name;
}
public class DataExample {
private final int id;
private String name;
public DataExample(final int id) {
this.id = id;
}
public int getId() {
return this.id;
}
public String getName() {
return this.name;
}
public void setName(final String name) {
this.name = name;
}
@Override
public boolean equals(final Object o) { … }
@Override
public int hashCode() { … }
@Override
public String toString() { … }
}

16. @Value
• final
• @ToString
• @EqualsAndHashCode
• @Getter
• @RequiredArgsConstructor
• Immutable

17. @Value
@Value
public class ValueExample {
private int id;
private String name;
}
public final class ValueExample {
private final int id;
private final String name;
public ValueExample(
final int id, final String name) {
this.id = id;
this.name = name;
}
public int getId() {
return this.id;
}
public String getName() {
return this.name;
}
@Override
public boolean equals(final Object o) { … }
@Override
public int hashCode() { … }
@Override
public String toString() { … }
}

18. @Builder
• Builder (GoF Effective
Java ) Builder
• Builder

19. @Builder
public static void main(String[] args) {
// Builder ( )
Customer customer = new Customer(
"Taro",
"Yamada",
"Tokyo",
Arrays.asList("A", "B"));
System.out.println(customer);
}
@AllArgsConstructor
@ToString
class Customer {
private String firstName;
private String lastName;
private String city;
private List<String> tags;
}
public static void main(String[] args) {
// Builder
Customer customer = Customer.builder()
.firstName("Taro")
.lastName("Yamada")
.city("Tokyo")
.tag("A")
.tag("B")
.build();
System.out.println(customer);
}
@Builder
@ToString
class Customer {
private String firstName;
private String lastName;
private String city;
@Singular
private List<String> tags;
}

20. @Slf4j
• log static Logger
• Slf4j Apache commons log(@Log)
• Logger

21. @Slf4j
@Slf4j
public class LogExample {
public static void main(String[] args) {
log.info("main.");
}
}
public class LogExample {
private static final org.slf4j.Logger log =
org.slf4j.LoggerFactory.getLogger(LogExample.class);
public static void main(String[] args) {
log.info("main.");
}
}

22. @NonNull
• null
(null
NullPointerException )
• Objects.requireNonNull

23. @NonNull
@RequiredArgsConstructor
public class NonNullExample {
@NonNull
private String name;
public void printLength(
@NonNull String message) {
System.out.println(
message.length());
}
}
public class NonNullExample {
@NonNull
private String name;
public void printLength(
@NonNull String message) {
if (message == null) {
throw new NullPointerException("message");
}
System.out.println(message.length());
}
public NonNullExample(
@NonNull final String name) {
if (name == null) {
throw new NullPointerException("name");
}
this.name = name;
}
}

24. val
•
• Scala val

25. val
public static void main(String[] args) {
val list = new ArrayList<String>();
list.add("a");
list.add("b");
val item = list.get(0);
System.out.println(item);
}
public static void main(String[] args) {
final ArrayList<String> list =
new ArrayList<String>();
list.add("a");
list.add("b");
final String item = list.get(0);
System.out.println(item);
}

26. @Cleanup
•
( )
close
• try/finally
• close

27. @Cleanup
public static void main(String[] args) throws IOException {
Path filePath = Paths.get(args[0]);
@Cleanup BufferedReader reader = Files.newBufferedReader(filePath);
System.out.println(reader.readLine());
}
public static void main(String[] args) throws IOException {
Path filePath = Paths.get(args[0]);
BufferedReader reader = Files.newBufferedReader(filePath);
try {
System.out.println(reader.readLine());
} finally {
if (Collections.singletonList(reader).get(0) != null) {
reader.close();
}
}
}

28. @Synchronized
• synchronized
• static
Lock
• Lock

29. @Synchronized
public class SynchronizedExample {
@Synchronized
public static void hello() {
System.out.println("hello");
}
@Synchronized
public void bye() {
System.out.println("bye");
}
}
public class SynchronizedExample {
private static final Object $LOCK = new Object[0];
private final Object $lock = new Object[0];
public static void hello() {
synchronized (SynchronizedExample.$LOCK) {
System.out.println("hello");
}
}
public void bye() {
synchronized (this.$lock) {
System.out.println("bye");
}
}
}

30. @SneakyThrows
• (
)
•
•
• https://github.com/rzwitserloot/lombok/blob/master/src/core/
lombok/Lombok.java#L49
• Lombok
Lombok jar

31. @SneakyThrows
public class SneakyThrowsExample {
@SneakyThrows
public static void main(String[] args) {
throw new Exception();
}
}
public class SneakyThrowsExample {
public static void main(String[] args) {
try {
throw new Exception();
} catch (final Throwable $ex) {
throw Lombok.sneakyThrow($ex);
}
}
}

32. delombok
• delombok Lombok
• delombok
• https://projectlombok.org/features/delombok
> java -jar lombok.jar delombok src -d src-delomboked

33. • Lombok
onMethd onParam
• https://projectlombok.org/features/experimental/onX

34. Lombok
•
•
• getter/setter
•
• equals hashCode

35. Lombok
•
• Lombok
• Lombok
Lombok
• val @Cleanup @SneakyThrows
(Lombok
)

36. •
Lombok
• https://projectlombok.org/features/all