[JAVA] Spring Boot for annotation learning

It is for my own learning.

I started using Spring in my current project.

I don't understand the annotations that are characteristic of Java and Spring => Efficient implementation is not possible. Spring has not been used effectively.

The one in App.java @SpringBootApplication The class with this annotation indicates that it is a Spring Boot application class. There is a run method that boots Spring. It is used when you want to add various setting information at the time of execution.

@EnableScheduling Enable the schedule function. -> Allow use of @Scheduled

@Scheduled You can specify the execution time of the method. Periodic execution can be performed by taking the following arguments to the annotation. You can also use cron. Details ⇒ https://qiita.com/rubytomato@github/items/4f0c64eb9a24eaceaa6e

Lombok (the one that automatically creates getters and setters) related annotations There are three types. @NoArgsConstructor,@RequiredArgsConstructor, @AllArgsConstructor

These three are annotations that automatically generate a constructor when creating getters / setters with lombok.

@ NoArgsConstructor Generates a default constructor with no arguments. @ RequiredArgsConstructor creates a constructor with arguments to set values in fields with final. @ AllArgsConstructor Generates a constructor that takes initialization values for all fields as arguments

Behavior of RequiredArgsConstructor

import lombok.RequiredArgsConstructor;

@RequiredArgsConstructor
public class Employee {

    private final int id;

    private String name;
}

Generated code

public class Employee {
    private final int id;
    private String name;

    public Employee(final int id) {
        this.id = id;
    }
}
//Names without the final qualifier are not included in the constructor.

In ongoing PJ It is used in the form of @ RequiredArgsConstructor (onConstructor = @ __ ( @ Autowired)).

onConstructor = @ __ ( @ Autowired)) I wondered what (?), So I looked it up. According to the official Lambok documentation, it's placed to annotate the generated constructor (!?) https://projectlombok.org/features/constructor About onX-> OnConstructor, it was written as follows. "we heard you like annotations, so we put annotations in your annotations so you can annotate while you're annotating." "We heard that you like annotations, so I put them in your annotations, so you can annotate while you're annotating."