Introduction to the JSR 303 verification constraints in the Java class library

Introduction to the JSR 303 verification constraint framework in the Java class library introduction: The JSR 303 verification constraint framework is a powerful verification and constraint mechanism provided by the Java class library that can be used to verify whether the attribute value of the Java object meets specific conditions.This article will introduce the basic concepts, working principles, and how to use it to improve the reliability of code. Overview: When developing applications, it is often necessary to verify the data entered by the user or ensure the legality of the object attribute.Traditional verification methods are usually manual compilation of verification logic, which is prone to errors and cumbersome.The JSR 303 verification constraint framework aims to simplify the verification process and provide a standardized verification mechanism. Developers can define the verification rules by annotating to avoid heavy manual verification work. working principle: The JSR 303 verification constraint framework is implemented based on annotations and reflection mechanisms.Developers can define verification rules by adding annotations to the attributes of the Java object, such as@notnull,@min,@max, etc.When running, the verification framework will scan the attribute of the object, obtain the annotation information, and verify the validity of the attribute value according to the annotation.When the verification is not approved, the framework will throw an abnormality or return the verification results to the developers. Example code: Below is a simple example code, showing how to use the JSR 303 verification constraint framework: public class User { @Notnull (Message = "Username cannot be empty") private String username; @Min (Value = 18, Message = "Age cannot be less than 18 years") @Max (Value = 60, Message = "Age cannot be greater than 60 years") private int age; // omit the getter and setter method } public class Main { public static void main(String[] args) { User user = new User(); user.setusername (null); // Verify that the user name cannot be empty user.setage (17); // Verify that the age cannot be less than 18 years old ValidatorFactory factory = Validation.buildDefaultValidatorFactory(); Validator validator = factory.getValidator(); Set<ConstraintViolation<User>> violations = validator.validate(user); for (ConstraintViolation<User> violation : violations) { System.out.println(violation.getMessage()); } } } The above code defines a User class. Among them, the username attribute uses the @Notnull annotation constraint as non -empty, and the AGE attributes use @Min and @max annotation constraints as an integer between 18 and 60.In the main method of the main class, a User object is created and the attribute values that violate the constraints are set up.Through ValidatorFactory and Validator objects, the User object can be verified and the verification results can be obtained.In the above examples, the verification results are "user names cannot be empty" and "age cannot be less than 18 years old." Summarize: The JSR 303 verification constraint framework provides a simple verification mechanism for the Java class library. By using annotation definition verification rules, the effectiveness of the attribute value can be quickly and reliable.By reducing manual verification and repeated code, this framework not only improves the reliability of code, but also improves development efficiency.For the Java application that needs to be verified, using the JSR 303 verification constraint framework is a good choice.