Using Lombok Annotations @RequiredArgsConstructor, @Delegate, @Cleanup, @Singular and @Builder in Spring Applications

The article introduces several Lombok annotations that can simplify Java code, especially when used together with Spring framework components.

@RequiredArgsConstructor (onConstructor = @__(@Autowired)) allows Lombok to generate a constructor that is automatically annotated with @Autowired , enabling Spring to inject required beans without writing boilerplate code.

@Service
@RequiredArgsConstructor(onConstructor = @__(@Autowired))
public class MyService {
    private final AnotherService anotherService;
}

Lombok expands the above to a class containing a constructor annotated with @Autowired , which Spring uses for dependency injection.

@Service
public class MyService {
    private final AnotherService anotherService;

    @Autowired
    public MyService(AnotherService anotherService) {
        this.anotherService = anotherService;
    }
}

@Delegate lets a class expose the methods of another class without manually delegating each method. By annotating a field with @Delegate , Lombok generates forwarding methods.

// A class with a method
public class A {
    public void sayHello() {
        System.out.println("Hello");
    }
}

// B delegates A's methods
public class B {
    @Delegate
    private A a = new A();

    public static void main(String[] args) {
        B b = new B();
        b.sayHello(); // calls A.sayHello()
    }
}

@Cleanup automatically wraps a resource in a try‑finally block and calls the specified cleanup method (default close ) when the scope ends.

@Cleanup InputStream in = new FileInputStream("some/file");

For resources with a different release method, the method name can be supplied:

@Cleanup("release") MyResource resource = new MyResource();

@Builder together with @Singular enables fluent, type‑safe construction of objects, especially when the class contains collection fields. @Singular generates methods to add single elements or whole collections, and the built collection becomes immutable.

@Data
@Builder
public class User {
    private String name;
    private int age;
    @Singular
    private List
hobbies;
}

User user = User.builder()
    .name("练习时长两年半")
    .age(28)
    .hobby("篮球")
    .hobby("唱歌")
    .hobbies(Arrays.asList("跳舞", "其他"))
    .build();

The article concludes by warning that while Lombok greatly reduces boilerplate, excessive or inappropriate use can make code harder to understand and maintain, so developers should apply it judiciously.