Understanding JSR-303 Annotations

The JSR 303 bean validation annotations are defined as part of the javax.validation package. Some important Validation Annotations are defined below:

1. @NotNull: Ensures the annotated element is not null.

Example:

public class Student {
    @NotNull(message = "Student name cannot be null")
    private String name;
}

2. @NotEmpty: Checks if a String, Collection, Map, or array is not empty.

Example:

public class Student {
    @NotEmpty(message = "List of marks cannot be empty")
   private List<String> marks;
}

It is also applied to strings, collections, and arrays.

3. @Size Checks if the size is between the specified boundaries.

Example:

public class Student {
    @Size(min = 18, message = "age cannot be less than ")
    private String age;
}

4. @Min and @Max: Limits the value of a numerical property, specifying the minimum or maximum allowed value.

Example:

public class Student {
  @Min(value = 1, message = "Student should have enrolled in at least one subject")     
  @Max(value = 4, message = "Student cannot be enrolled more than four subjects")
    private double subject;
}

5. @Pattern: Checks if a String matches the given regular expression.

Example:

public class Student {
    @Pattern(regexp = "\\d{3}-\\d{3}-\\d{4}", message = "Kindly Provide a Valid phone number")
    private String phoneNumber;
}

6. @Email: Checks if a String is a valid email address.

Example:

public class Student {
    @NotNull
    @Email(message = "Please provide a valid email address")
    private String email;
}

7. @URL: Checks if a String is a valid URL.

Example:

public class Student {
    @URL(message = "Please enter a valid Website")
    private String website;
}

8. @Past: Checks if a date/time is in the past.

Example:

public class Student {
    @Past(message ="Please enter a valid Date")
    private LocalDate dateOfBirth;
}

9. @Future: Checks if a date/time is in the future.

Example:

public class Admin {
    @Future(message = "Due date must be in the future")
    private Date admissionDueDate;
}

10. @DecimalMin and @DecimalMax: Checks decimal number ranges.

Example:

public class Admin {
  @DecimalMin("100000.50")
  @DecimalMax("200000.00")
  private BigDecimal fees;
}

11. @Digits: Checks the number of digits of an integer or decimal number.

Example:

public class Student {
  @Digits(integer = 5, fraction = 2)
  private double percentage;
}

12. @AssertTrue/False: Checks if a boolean expression is true/false.

Example:

In this article, we’ll explore practical examples of how to apply JSR-303 annotations to your domain objects from basic annotations to advanced. So basically annotations provide a declarative way to configure Spring beans, manage dependencies, and define behaviors, reducing the need for boilerplate code and making your code more concise and expressive.