[JAVA] Specify the default value with @Builder of Lombok

Postscript (2017/9/10)

From v1.16.16, you can specify the default value by adding the @ Builder.Default annotation.

@Builder
public class Coupon {
    @Builder.Default
    private UUID id = UUID.randomUUID();
    private String name;
    private String description;
    private ZonedDateTime expireDate;
}

By the way, Spring Boot was imported in v1.5.3, so if you are using an earlier version, you need to explicitly specify the version.

Overview

Lombok's @Builder is an annotation that automatically generates a builder class for a specified class.

@Value
@Builder
public class Coupon {
    private UUID id;
    private String name;
    private String description;
    private ZonedDateTime expireDate;
}

Coupon coupon = Coupon.builder()
        .name("Surprised coupon")
        .description("Surprised coupon")
        .expireDate(ZonedDateTime.parse("2017-01-30T23:59:59+09:00", DateTimeFormatter.ISO_OFFSET_DATE_TIME))
        .build();

However, the property for which no value is specified in the builder call will be null. Even if you try to set a default value other than null and write it in the target class as follows, it will not work.

@Value
@Builder
public class Coupon {
    private UUID id = UUID.randomUUID(); //Does not apply
    private String name = "";            //Does not apply
    private String description;
    private ZonedDateTime expireDate;
}

Therefore, this time, I will introduce how to set the default value correctly.

How to set the default value for @ Builder

To set the default value, describe the builder class with the naming convention of target class name + Builder as shown below. The rest is nicely complemented by Lombok.

@Value
@Builder
public class Coupon {
    private UUID id;
    private String name;
    private String description;
    private ZonedDateTime expireDate;

    public static class CouponBuilder {
        private UUID id = UUID.randomUUID();
        private String name = "";
    }
}

reference

• @Builder
• Using Lombok’s @Builder annotation with default values