Common annotations for Java Bean Validation include: 1. @NotNull verification field is not empty; 2. @NotBlank verification string is not blank; 3. @Size limits length or size; 4. @Min / @Max controls the numerical range; 5. @Email verify the mailbox format; verification triggers can be added by adding @Valid before the Controller parameter of Spring MVC and cooperating with BindingResult; custom constraints need to create annotations and implement the ConstraintValidator interface; verification packets can be used to verify different scenarios by specifying groups attributes and defining interfaces.
Java data verification is a very common requirement in development, especially when processing user input or external data sources. The Bean Validation API (JSR 380) provides a standard way to constrain and verify the properties of Java objects, which is simple and practical to use.
What are the common annotations?
Bean Validation provides some commonly used annotations to define rules, such as:
-
@NotNull: The field cannot be null -
@NotBlank: String cannot be blank (only applicable to String types) -
@Size(min =, max =): Controls string length, collection size, etc. -
@Min/@Max: Limit the numerical range -
@Email: Check whether it is a legal email format
These annotations can be added directly to the fields of the entity class, such as:
public class User {
@NotBlank(message = "The name cannot be empty")
private String name;
@Email(message = "The email format is incorrect")
private String email;
}The benefits of this approach are clear logic, easy to maintain, and easy to integrate with frameworks such as Spring.
How to trigger verification?
In Spring MVC, if you @Valid the Controller method parameters, Spring will automatically trigger Bean Validation:
@PostMapping("/users")
public ResponseEntity<?> createUser(@Valid @RequestBody User user, BindingResult result) {
if (result.hasErrors()) {
return ResponseEntity.badRequest().body(result.getAllErrors());
}
// Handle business logic}A few points to note here:
-
@Validmust be used withBindingResult, otherwise the exception will not be caught, but will directly throw MethodArgumentNotValidException - If you have nested objects, you also need to add
@Validto verify internal objects if you want to add - You can customize the exception handler to return the error message structure uniformly
How to write custom constraints?
Sometimes built-in annotations cannot meet your business needs. For example, you need to verify the mobile phone number format, ID number, etc., and you need to customize the annotations at this time.
The steps are roughly like this:
- Create an annotation, such as
@PhoneNumber - Implement
ConstraintValidator<@PhoneNumber, String>interface - Write specific verification logic in the validate method
- Add this annotation to the field and you can use it
For example, if you want to do mobile phone number verification, you can write it like this:
@Target({ FIELD })
@Retention(RUNTIME)
@Constraint(validatedBy = PhoneValidator.class)
public @interface PhoneNumber {
String message() default "The mobile phone number format is incorrect";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}Then implement validator:
public class PhoneValidator implements ConstraintValidator<PhoneNumber, String> {
@Override
public boolean isValid(String value, ConstraintValidatorContext context) {
return value != null && value.matches("\\d{11}");
}
}This can be used in entity classes:
@PhoneNumber private String mobile;
How to use verification grouping?
Sometimes, we want different operations to use different verification rules. For example, adding new users requires verification of all fields, but only some fields are needed when updating.
At this time, the verification grouping function can be used. The specific method is to specify groups attribute in the annotation of the field and create an empty interface to represent different groups:
public interface CreateGroup {}
public interface UpdateGroup {}
public class User {
@NotBlank(groups = {CreateGroup.class})
private String name;
@NotBlank(groups = {UpdateGroup.class})
private String email;
}Then pass the corresponding group in the Controller:
@Validated(CreateGroup.class)
This will allow you to flexibly control the verification rules in different scenarios.
Basically that's it. The core of Bean Validation is to restrict object properties through annotation, and then automatically trigger verification with the framework, which is both standardized and convenient. However, it should be noted that although it is suitable for basic data format verification, if it involves complex business rules judgments, it is recommended to be placed in the Service layer.
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