Code Generation with tools such as Groovy, Lombok, AutoValue and Immutables will reduce boilerplate from your code and makes it more readable. An overview of creating value objects, immutability and how they do annotation processing.

1. Ted’s Tool Time
Ted Vinke
First8
Code Generation with Groovy,
Lombok, AutoValue and Immutables
July 2016

2. Reducing
boilerplate

3. Project Lombok
https://projectlombok.org/
@NonNull
@Cleanup
@Getter / @Setter
@ToString
@EqualsAndHashCode
@NoArgsConstructor,
@RequiredArgsConstructor and
@AllArgsConstructor

4. Project Lombok
import lombok.AllArgsConstructor;
import lombok.EqualsAndHashCode;
import lombok.ToString;
@ToString
@AllArgsConstructor
@EqualsAndHashCode
public class Person
{
private String lastName;
private String firstName;
}

5. Value objects

6. Immutability in
plain old Java
● final
● final private
● construction in a single step
● defensive copying
● no mutators
● ...
public final class Planet {
private final double mass;
private final String name;
private final Date dateOfDiscovery;
public Planet (double mass, String mame, Date dateOfDiscovery) {
this.mass = mass;
this.name = name;
this.dateOfDiscovery = new Date(dateOfDiscovery.getTime());
}
public double getMass() {
return mass;
}
public String getName() {
return name;
}
public Date getDateOfDiscovery() {
return new Date(dateOfDiscovery.getTime());
}
}

7. Equals, hashCode
in plain-old Java
public final class Location {
private final String countryCode;
private final int priority;
public Location(String countryCode, int priority) {
this.countryCode = countryCode;
this.priority = priority;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((countryCode == null) ? 0 :
countryCode.hashCode());
result = prime * result + priority;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (!(obj instanceof Location))
return false;
Location other = (Location) obj;
if (countryCode == null) {
if (other.countryCode != null)
return false;
} else if (!countryCode.equals(other.countryCode))
return false;
if (priority != other.priority)
return false;
return true;
}
}

8. @Value
Project Lombok
import lombok.experimental.Value;
@Value
public class Location {
String countryCode;
int priority;
}

9. Groovy
http://www.groovy-lang.org/

10. And...
Dates, Cloneables and arrays are
defensively copied on the way
in (constructor) and out
(getters).
Collections and Maps are wrapped
by immutable wrapper classes.
@Immutable
import groovy.transform.Immutable
@Immutable
class Location {
String countryCode
int priority
}

11. AutoValue
https://github.com/google/auto/tree/
master/value
Generated immutable value classes for
Java 1.6+

12. @AutoValue
Google AutoValue
import com.google.auto.value.AutoValue;
@AutoValue
abstract class Location {
static Location create(String countryCode, int priority) {
return new AutoValue_Location(countryCode, priority)
}
abstract String countryCode()
abstract int priority()
}

13. Generated
AutoValue_Location.java
import javax.annotation.Generated;
@Generated("com.google.auto.value.processor.AutoValueProcessor")
final class AutoValue_Location extends Location {
private final String countryCode;
private final int priority;
AutoValue_Location(
String countryCode,
int priority) {
if (countryCode == null) {
throw new NullPointerException("Null countryCode");
}
...
}
@Override
String countryCode() {
return countryCode;
}

14. Immutables
http://immutables.github.io/

15. @Value.Immutable
import org.immutables.value.Value;
@Value.Immutable
abstract class Location {
abstract String countryCode()
abstract int priority()
}

16. Generated
ImmutableLocation.java
import javax.annotation.Generated;
@SuppressWarnings("all")
@Generated({"Immutables.generator", "Location"})
final class ImmutableLocation extends Location {
private final String countryCode;
private final int priority;
private ImmutableLocation(String countryCode, int
priority) {
this.countryCode = countryCode;
this.priority = priority;
}
@Override
String countryCode() {
return countryCode;
}
public static ImmutablePerson.Builder builder() {
return new ImmutablePerson.Builder();
}

17. Annotation processing
Lombok, AutoValue, and Immutables all employ annotation processing via
javac, Groovy uses groovyc
AutoValue and Immutables generate new source - which extend template class
e.g. Location.java -> AutoValue_Location.java extends Location
Groovy and Lombok modify the AST and enhances compiled class

18. That's it!
Project Lombok - https://projectlombok.org/
Groovy - http://www.groovy-lang.org/
AutoValue - https://github.com/google/auto/blob/master/value
Immutables - http://immutables.github.io/
http://culttt.com/2014/04/30/difference-entities-value-objects/
http://marxsoftware.blogspot.nl/2016/06/lombok-autovalue-immutables.html
Thank you