Additional methods in java Builder class (lombok annotation)

Question

SO, I have class that uses @Builder lombok annotation. This is how it looks and how I use it:

 import lombok.Builder; import lombok.Data; import com.fasterxml.jackson.annotation.JsonProperty; @Data @Builder public class MyModel { @JsonProperty(value = "myField1") private String myField1; @JsonProperty(value = "myField2") private String myField2; @JsonProperty(value = "myField3") private String myField3; } //This is how I use it: MyModel model = MyModel.builder() .myField1("value for field 1") .myField2("value for field 2") .build(); 

My question is if it is a good practice or not to add some additional method to this class? Or I should leave it as it is and do any business logic outside??

Basically, lets say, I need a helper method to set myField3 property, because I CANNOT just to do:

  .myField3("value for field 3") .build() 

I need to perform some actions on value for field3 and after that set it to MyModel.

So can I put this helper method to this class?

Answer 1

According to Lombok's Builder documentation ,

Each listed generated element will be silently skipped if that element already exists (disregarding parameter counts and looking only at names). This includes the builder itself: If that class already exists, lombok will simply start injecting fields and methods inside this already existing class, unless of course the fields / methods to be injected already exist. You may not put any other method (or constructor) generating lombok annotation on a builder class though; for example, you can not put @EqualsAndHashCode on the builder class.

So can I put this helper method to this class?

Yes, you can by having a minimal builder which provides a method with the same name as the field, ie, myField3 . The business logic can be added to this method. Here is a simple example where "Hello" is prepended to the value provided by the setter,

@Data
@Builder
public class MyModel {

    private String myField1;

    private String myField2;

    private String myField3;

    public static class MyModelBuilder {
        public MyModelBuilder myField3(String myField3) {
            this.myField3 = "Hello " + myField3;
            return this;
        }
    }
}

Here is an example of using your class,

MyModel model = MyModel.builder()
                .myField1("value for field 1")
                .myField2("value for field 2")
                .myField3("value for field 3")
                .build();