1. Overview
In this quick tutorial, we’ll take a look at JSR-330‘s @Size, Hibernate‘s @Length and JPA @Column‘s length attribute.
At first blush, these may seem the same, but they perform different functions. Let’s see how.
2. Origins
Simply put, all of these annotations are meant to communicate the size of a field.
@Size and @Length are similar. We can use either to validate the size of a field. The first is a Java-standard annotation and the second is specific to Hibernate.
@Column, though, is a JPA annotation that we use to control DDL statements.
Now, let’s go through each of them in detail.
3. @Size
For validations, we’ll use @Size, a bean validation annotation. Let’s use the property middleName annotated with @Size to validate its value between the attributes min and max:
public class User {
// ...
@Size(min = 3, max = 15)
private String middleName;
// ...
}
Most importantly, @Size makes the bean independent of JPA and its vendors such as Hibernate. As a result, this is more portable than @Length.
4. @Length
And as we just stated, @Length is the Hibernate-specific version of @Size. Let’s enforce the range for lastName using @Length:
@Entity
public class User {
// ...
@Length(min = 3, max = 15)
private String lastName;
// ...
}
5. @Column(length=value)
@Column, though, is quite different.
We’ll use @Column to indicate specific characteristics of the physical database column. Let’s use the length attribute of the @Column annotation to specify the string-valued column length:
@Entity
public class User {
@Column(length = 3)
private String firstName;
// ...
}
Consequently, the resulting column would be generated as a VARCHAR(3) and trying to insert a longer string would result in an SQL error.
Note that we’ll use @Column only to specify table column properties as it doesn’t provide validations.
Of course, we can use @Column together with @Size to specify database column property with bean validation.
@Entity
public class User {
// ...
@Column(length = 5)
@Size(min = 3, max = 5)
private String city;
// ...
}
6. Conclusion
In this write-up, we learned about the differences between the @Size annotation, @Length annotation and @Column‘s length attribute. We examined each separately within the areas of their use.
As always, the full source code of the examples is available over on GitHub.