java 当我们使用 lombok builder 有继承关系时如何构建对象？

How to build an object when we have inheritance relationship using lombok builder?

提问by Rakesh

In my project, I am using lombok to avoid writing getters and setters for a class. Also, I am using lombok.Builder to build an object instead of writing new Obeject() and then setting all the values.

在我的项目中，我使用 lombok 来避免为类编写 getter 和 setter。此外，我正在使用 lombok.Builder 来构建一个对象，而不是编写 new Obeject() 然后设置所有值。

But when we have inheritance relationship and when we want to construct child object using lombok builder, I am not getting parent's field.

但是当我们有继承关系并且我们想使用 lombok builder 构造子对象时，我没有得到父级的字段。

For example:

例如：

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
@EqualsAndHashCode
public class Parent{
  private String nationality;
  .
  .
  // more columns
}

And Child class would be something like this:

Child 类将是这样的：

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@ToString(callSuper = true)
@EqualsAndHashCode(callSuper = true)
public class Child extends Parent{
   private String firstName;
   private String lastName;
   .
   .
}

In my test class, where I need to build child object

在我的测试类中，我需要在其中构建子对象

public class Test{

 public void testMethod(){
   Child child = Child.builder()
            .firstName("Rakesh")
            .lastName("SS")
            .nationality("some text")// I am not able to set nationality               
            .build();
 }


}

Please let me know, is there any way to handle this scenario in lombok.

请让我知道，有没有办法在 lombok 中处理这种情况。

回答by Jeff

@Builderhas no way to determine which fields of Parentyou wish to expose.

@Builder无法确定Parent您希望公开哪些字段。

When @Builderis placed on a class, only fields explicitly declared on that class are added to the *Builder.

当@Builder放在一个类上时，只有在该类上显式声明的字段才会添加到*Builder.

When @Builderis placed on a static method or a constructor the resulting *Builderwill have a method for each argument.

当@Builder放置在静态方法或构造函数上时，结果*Builder将具有每个参数的方法。

Also if you are using @Builderthen is it safe to assume that at least Childis meant to be immutable?

此外，如果您正在使用，@Builder那么假设至少Child是不可变的是否安全？

I supply two examples, one where Parentis mutable and Childis immutable and one where both Parentand Childare immutable.

我提供了两个例子，一个Parent是可变和Child不可变的，一个是Parent和Child都是不可变的。

Immutable Parent and Child

不可变的父子

import static org.junit.Assert.*;
import lombok.Builder;
import lombok.EqualsAndHashCode;
import lombok.ToString;
import lombok.Value;
import lombok.experimental.NonFinal;

import org.junit.Test;

public class So32989562ValueTest {

    @Value
    @NonFinal
    public static class Parent {

        protected final String nationality;

    }

    @Value
    @ToString(callSuper = true)
    @EqualsAndHashCode(callSuper = true)
    public static class Child extends Parent {

        private final String firstName;

        private final String lastName;

        @Builder(toBuilder = true)
        private Child(String nationality, String firstName, String lastName) {
            super(nationality);
            this.firstName = firstName;
            this.lastName = lastName;
        }
    }

    @Test
    public void testChildBuilder() {

        String expectedFirstName = "Jeff";
        String expectedLastName = "Maxwell";
        String expectedNationality = "USA";

        Child result = Child.builder()
            .firstName(expectedFirstName)
            .lastName(expectedLastName)
            .nationality(expectedNationality)
            .build();

        assertEquals(result.toString(), expectedFirstName, result.getFirstName());
        assertEquals(result.toString(), expectedLastName, result.getLastName());
        assertEquals(result.toString(), expectedNationality, result.getNationality());
    }
}

Mutable Parent, Immutable Child:

可变父级，不可变子级：

import static org.junit.Assert.*;
import lombok.Builder;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.ToString;
import lombok.Value;

import org.junit.Test;

public class So32989562DataTest {

    @Data
    public static class Parent {

        protected String nationality;

    }

    @Value
    @ToString(callSuper = true)
    @EqualsAndHashCode(callSuper = true)
    public static class Child extends Parent {

        private final String firstName;

        private final String lastName;

        @Builder(toBuilder = true)
        private Child(String nationality, String firstName, String lastName) {
            this.setNationality(nationality);
            this.firstName = firstName;
            this.lastName = lastName;
        }
    }

    @Test
    public void testChildBuilder() {

        String expectedFirstName = "Jeff";
        String expectedLastName = "Maxwell";
        String expectedNationality = "USA";

        Child result = Child.builder()
            .firstName(expectedFirstName)
            .lastName(expectedLastName)
            .nationality(expectedNationality)
            .build();

        assertEquals(result.toString(), expectedFirstName, result.getFirstName());
        assertEquals(result.toString(), expectedLastName, result.getLastName());
        assertEquals(result.toString(), expectedNationality, result.getNationality());
    }
}

回答by Amit Kaneria

Above solution works, however that requires too much workaround. And further any changes in child and parent class requires changing constructor arguments everywhere.

上述解决方案有效，但这需要太多的解决方法。此外，子类和父类的任何更改都需要在任何地方更改构造函数参数。

Lombok has introduced experimental features with version: 1.18.2 for inheritance issues faced with Builder annotation, and can be resolved with @SuperBuilder annotation as below.

Lombok 已经在 version: 1.18.2 中引入了实验性功能，用于解决 Builder 注解面临的继承问题，可以使用 @SuperBuilder 注解解决，如下所示。

@SuperBuilder
public class ParentClass {
    private final String a;
    private final String b;
}

@SuperBuilder
public class ChildClass extends ParentClass{
    private final String c;
}

Now, one can use Builder class as below (that was not possible with @Builder annotation)

现在，可以使用如下的 Builder 类（@Builder 注释无法实现）

ChildClass.builder().a("testA").b("testB").c("testC").build();