Annotation and its role in the Bean Validation API framework

Bean Validation API is part of the Java EE specification, which aims to provide a strong verification framework for applications.It declares the verification and constraint by adding annotations to the object attribute, so that the verification logic can be automatically executed to ensure the effectiveness and consistency of the data.Here are some important annotations and functions in the Bean Validation API framework: 1. @NotNull： Function: Used to mark attributes cannot be null. Example: @Notnull Private String Username; 2. @Size： Function: Limit the length or size of the marking attribute. 示例：@Size(min = 2, max = 50) private String name; 3. @Email： Function: For labeling attributes, it must be an effective email address. Example: @email Private String Email; 4. @Pattern： Function: The marking attribute must be matched with the specified regular expression. 示例：@Pattern(regexp = "^[A-Za-z]+$") private String username; 5. @min and @Max: Function: The value range limit for marking attributes indicates minimum values and maximum values, respectively. Example: @min (18) @max (100) Private int Age; 6. @DecimalMin和@DecimalMax： Function: Limited by the number range for marking attributes, respectively represent the minimum value and maximum value, respectively. 示例：@DecimalMin("0.0") @DecimalMax("10.0") private double score; 7. @asserttrue 和 @assertfalse ： Function: The marking attribute must be true or false. Example: @Asserttrue Private Boolean Enabled; 8. @Past and @Future: Function: The marking attribute must be the past or future date. 示例：@Past private Date birthdate; 9. @Valid： Function: It is used to mark the attribute as an nested verification object.This can verify the associated objects by recursive verification. 示例：@Valid private Address address; The above is only some commonly used annotations in the Bean Validation API framework, as well as other annotations for use.To use these annotations, the necessary configuration is required in the application.This includes the dependency item of adding the Bean Validation API to the Maven or Gradle constructing files, and adding corresponding annotations to the class or method required for verification. For example, in the Spring framework, an annotation can be added to the attributes of the Bean class, and the target object that is used as a form data binding of the form data can be added.When submitting a form, Spring will automatically perform verification based on the annotation and return the verification results to the client. Please note that the Bean Validation API only provides a verification framework. Developers still need to be appropriately wrongly handled and message display mechanisms to deal with the failure of the verification. In summary, annotations in the Bean Validation API framework provides a simple and convenient way to define and execute verification constraints to ensure the effectiveness and consistency of the data.It is very useful when developing Java applications and helps reduce the workload of manual compilation and verification logic.