A guide to Annotations in Spring Boot

If you are a Spring Boot developer, or you just started the road in this town, you must have used various kinds of annotations. When I started my first project, I used them just to get the project done but then I started exploring them and jotted them down for my easy understanding. Here I list some of the annotations which are commonly used in entity class with their meanings and use.

For this post, I am going to cover all the annotations covered in this piece of code:

@Entity
@Table(name="User")
@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
public class User {
    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "USER_NAME", length = 50, nullable = false, unique = true)
    private String userName;

    @Column(name="FIRST_NAME", length = 50, nullable = false)
    private String firstName;

    @Column(name="LAST_NAME", length = 50, nullable = false)
    private String lastName;

    @Column(name="EMAIL", length = 50, nullable = false)
    private String email;

    @Column(name = "ROLE", length = 50, nullable = false)
    private String role;

}

Entity

JPA Annotation: @Entity
Used to mark a POJO class in Java as persistence table in the database
It converts each variable in the POJO class as a field/column in table

Eg:

      @Entity
      public class Demo{
      }

Table

JPA Annotation: @Table
This is used to name the table. We can change entity name using this. And it is not necessary to have the same entity and table name.

NoArgsConstructor

JPA Annotation: @NoArgsConstructor
This annotation is provided by Lombok dependency
It generates a default constructor for class with no parameters

AllArgsConstructor

JPA Annotation: @AllArgsConstructor
This annotation is provided by Lombok dependency
It generates a constructor requiring an argument for every field/variable in the annotated class(entity)

Getter

JPA Annotation: @Getter
Provided by Lombok dependency
Provides getter methods for every field

Setter

JPA Annotation: @Setter
Provided by Lombok dependency
Provides setter methods for every field

ToString

JPA Annotation: @ToString
Provided by Lombok dependency
Provides toString() method for the annotated class

Id

JPA Annotation: @Id
Marks the field as the primary key in the table

GeneratedValue

JPA Annotation: @GeneratedValue
This is to specify how the primary key must be generated.
It has many strategies for generating keys, default is Auto which is like Auto_Increment in MySql

Column(name, length, nullable, unique)

JPA Annotation: @Column
This is to specify the column properties like name, length of value(if a string), it can be null or not and then unique which defines if the column value should be unique

I will bring more in part 2 of this post. This is my first post, so I would love to hear what I can do better.

A guide to Annotations in Spring Boot - Part 1