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, i.e., 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();