How do Java enumeration types work with the Spring framework?

The enumeration type in the Spring framework is used to represent a set of predefined constant values. It is mainly used in the following ways: declare the enumeration type and use the @Enumerated annotation to specify the persistence strategy (EnumType.ORDINAL or EnumType.STRING). Practical cases: In the user rights management system, enumeration types can be used to represent user rights, and the @CollectionTable annotation is used to associate with the user model to easily manage user rights and persist enumeration constants.

The use of Java enumeration types in the Spring framework

In the Spring framework, enumeration types are used to represent an Group predefined constant values, for example:

public enum Role {
    ADMIN,
    USER,
    GUEST
}

The main ways to use enumeration types with the Spring framework are as follows:

1. Declare the enumeration type

First, you need to declare an enumeration type:

public enum Role {

    // 枚举常量
    ADMIN,
    USER,
    GUEST
}

2. Use the @Enumerated annotation

before using the enumeration type , you need to use the @Enumerated annotation to specify its persistence strategy. Spring provides two strategies:

• EnumType.ORDINAL: Stores the sequential values ​​of enumeration constants in the database (starting from 0).
• EnumType.STRING: Stores the string value of an enumeration constant in the database.

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Enumerated(EnumType.STRING)
    private Role role;
}

Practical case: User rights management

Consider a user rights management system in which users can have different rights. You can use the following enumeration type to represent permissions:

public enum Permission {
    READ,
    WRITE,
    DELETE
}

You can then associate the Permission enumeration type with a user model:

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String username;
    private String password;

    @Enumerated(EnumType.STRING)
    @CollectionTable(
            name = "user_permissions",
            joinColumns = @JoinColumn(name = "user_id")
    )
    @Column(name = "permission")
    private Set<Permission> permissions;
}

in User In the class, the permissions attribute is a Set<Permission>, used to store the user's permissions. By using the @CollectionTable annotation, Spring will use an auxiliary table to store the relationship between users and permissions.

This way, you can easily manage user permissions and use Spring's automatic conversion feature to convert between persistent objects and enumeration constants.

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