What are the practical application cases of combination pattern in java framework?

The combination mode is widely used in Java frameworks, such as: composite controller in Spring MVC: combine multiple sub-controllers, manage and call them uniformly. Entity inheritance in Spring Data JPA: The parent entity defines public properties, and the child entities inherit and add their own properties.

Practical application cases of composition pattern in Java framework

Composition pattern is a design pattern that allows you to combine objects into a tree structure to use a unified interface to operate a single object or its combination of objects. In the Java framework, the composition pattern has a wide range of applications.

Practical case: Composite controller in Spring MVC controller

Spring MVC provides the @Controller annotation to mark the controller class. We can use the composition mode to create composite controllers and manage multiple sub-controllers.

The following is the sample code:

@Controller
public class MainController {

    @Autowired
    private UserController userController;
    @Autowired
    private PostController postController;

    @RequestMapping("/")
    public String index() {
        // 调用子控制器方法
        userController.listUsers();
        postController.listPosts();
        return "index";
    }
}

In this example, MainController is used as a composite controller, combining UserController and PostController Child controller. When accessing the / path, MainController calls the listUsers() and listPosts() methods of the child controller to handle the request and return "index" view.

Practical case: Entity inheritance in Spring Data JPA

Spring Data JPA uses the composite pattern to implement entity inheritance. Parent entities can define public fields and methods, while child entities can inherit these properties and add their own specific fields and methods.

The following is the sample code:

// 父实体
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
class Person {

    @Id
    @GeneratedValue
    private Long id;
    private String name;

}

// 子实体
@Entity
public class Employee extends Person {

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