JSR 303 verification constraint framework Frequently Ascending questions

JSR 303 verification constraint framework Frequently Asked questions answers JSR 303 is a specification of Java, which is used to define and applied verification constraints.It provides a simple and powerful way to verify the attribute value of the Java object.The following are some common answers to the JSR 303 verification constraint framework. Question 1: What is the JSR 303 verification constraint framework? Answer: JSR 303 is part of the specification of Java Bean Validation. It defines a set of annotations and APIs to verify the attribute values of the Java object.By using these annotations, we can automatically verify the attributes of the object at runtime to ensure that they meet specific constraints. Question 2: How to apply the JSR 303 verification constraint framework in Java? Answer: To apply the JSR 303 verification constraint framework in Java, you need to add related dependencies.For example, the following dependencies can be added to the pom.xml file: <dependency> <groupId>javax.validation</groupId> <artifactId>validation-api</artifactId> <version>2.0.1.Final</version> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-validator</artifactId> <version>7.0.1.Final</version> </dependency> Then, in terms of the attributes of the Java class that need to be verified, the annotations provided by the JSR 303 are used for constraint definition.For example, using @Notnull annotation to verify that the attribute cannot be empty: public class User { @NotNull private String username; // omit other attributes and methods ... } Question 3: What commonly used verification annotations do JSR 303 provide? Answer: JSR 303 provides many commonly used verification annotations to define different constraints.Some common verification annotations include: -@Notnull: The validation of the verification attribute cannot be empty. -@Size: Verify whether the size of the attribute value meets the requirements. -@Min: The validity value must be greater than or equal to the specified minimum value. -@Max: The validation attribute must be less than or equal to the specified maximum value. -@Email: Verify whether the attribute value conforms to the email format. -@Pattern: Verify whether the attribute value meets the specified regular expression, etc. Question 4: How to make custom verification constraints? Answer: To define customized authentication constraints, you can create a new annotation and use @Constraint annotations for annotations.Then create a verification logic that implements the ConstraintValidator interface to make a custom verification logic.The following is an example of a customized verification constraint: @Target({ ElementType.FIELD }) @Retention(RetentionPolicy.RUNTIME) @Documented @Constraint(validatedBy = CustomValidator.class) public @interface CustomConstraint { String message() default "Invalid value"; Class<?>[] groups() default {}; Class<? extends Payload>[] payload() default {}; } public class CustomValidator implements ConstraintValidator<CustomConstraint, String> { @Override public void initialize(CustomConstraint constraintAnnotation) { } @Override public boolean isValid(String value, ConstraintValidatorContext context) { // Customized verification logic return value != null && value.startsWith("custom"); } } Then, you can use customized verification annotations in the attributes of the Java class: public class User { @CustomConstraint private String code; // omit other attributes and methods ... } Question 5: How to use the JSR 303 verification constraint framework in the Spring Boot project? Answer: It is very convenient to use the JSR 303 verification constraint framework in the Spring Boot project.Just add @valid annotations to the required request parameter object.For example, in the request processing method of the controller: @PostMapping("/users") public ResponseEntity<String> createUser(@Valid @RequestBody User user) { // Processing the logic of creating users return ResponseEntity.ok("User created successfully"); } In the above example,@Valid Note will tell Spring Boot to automatically execute the JSR 303 verification constraint and return the corresponding error information when the verification fails. Summarize: The JSR 303 verification constraint framework provides a simple and powerful way to verify the attribute value of the Java object.By using related annotations, we can define various constraints and automatically verify the attributes during runtime.This verification framework is widely used in Java development, especially in the framework of Spring Boot to improve the robustness and stability of the application.