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        （六）创建自定义约束

        本文介绍如何在Java中创建自定义Bean Validation约束。首先定义约束注释@CheckCase，使用@Target指定作用目标，@Retention(RUNTIME)确保运行时可用，@Constraint关联验证器，@Repeatable支持重复标注。然后实现ConstraintValidator接口创建验证器CheckCaseValidator，在initialize()中初始化参数，在isValid()中编写大小写校验逻辑。最后可通过payload区分错误严重程度。

        August 26, 20238 分钟 阅读17 次阅读

        有的时候博客内容会有变动，首发博客是最新的，其他博客地址可能会未同步,认准https://blog.zysicyj.top

        一、创建一个简单的约束

        1. 约束注释

        • 枚举表示大小写
        public enum CaseMode {
    UPPER,
    LOWER;
}
        • 定义@CheckCase约束
        import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE_USE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
@Target({ FIELD, METHOD, PARAMETER, ANNOTATION_TYPE, TYPE_USE })
@Retention(RUNTIME)
@Constraint(validatedBy = CheckCaseValidator.class)
@Documented
@Repeatable(List.class)
public @interface CheckCase {
    String message() default "{org.hibernate.validator.referenceguide.chapter06.CheckCase." +
            "message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
    CaseMode value();
    @Target({ FIELD, METHOD, PARAMETER, ANNOTATION_TYPE })
    @Retention(RUNTIME)
    @Documented
    @interface List {
        CheckCase[] value();
    }
}
        • 测试一下吧
        public class Severity {
    public interface Info extends Payload {
    }
    public interface Error extends Payload {
    }
}

        public class ContactDetails {
    @NotNull(message = "Name is mandatory", payload = Severity.Error.class)
    private String name;
    @NotNull(message = "Phone number not specified, but not mandatory",
            payload = Severity.Info.class)
    private String phoneNumber;
    // ...
}

        用法

        @Target 定义约束所支持的目标元素类型

        @Retention(RUNTIME)：指定此类型的注释将在运行时通过反射方式提供

        @Constraint(validatedBy = CheckCaseValidator.class)：将注释类型标记为约束注释，并指定用于验证元素的验证器

        @CheckCase。如果可以在几种数据类型上使用约束，则可以指定几个验证器，每种数据类型一个。

        @Repeatable(List.class)：表示注释可以在同一位置重复多次，通常使用不同的配置

        2. 约束验证器

        public class CheckCaseValidator implements ConstraintValidator<CheckCase, String> {
    private CaseMode caseMode;
    @Override
    public void initialize(CheckCase constraintAnnotation) {
        this.caseMode = constraintAnnotation.value();
    }
    @Override
    public boolean isValid(String object, ConstraintValidatorContext constraintContext) {
        if ( object == null ) {
            return true;
        }
        if ( caseMode == CaseMode.UPPER ) {
            return object.equals( object.toUpperCase() );
        }
        else {
            return object.equals( object.toLowerCase() );
        }
    }
}
        • 自定义错误消息
        public class CheckCaseValidator implements ConstraintValidator<CheckCase, String> {
    private CaseMode caseMode;
    @Override
    public void initialize(CheckCase constraintAnnotation) {
        this.caseMode = constraintAnnotation.value();
    }
    @Override
    public boolean isValid(String object, ConstraintValidatorContext constraintContext) {
        if ( object == null ) {
            return true;
        }
        boolean isValid;
        if ( caseMode == CaseMode.UPPER ) {
            isValid = object.equals( object.toUpperCase() );
        }
        else {
            isValid = object.equals( object.toLowerCase() );
        }
        if ( !isValid ) {
            constraintContext.disableDefaultConstraintViolation();
            constraintContext.buildConstraintViolationWithTemplate(
                    "{org.hibernate.validator.referenceguide.chapter06." +
                    "constraintvalidatorcontext.CheckCase.message}"
            )
            .addConstraintViolation();
        }
        return isValid;
    }
}
        • HibernateConstraintValidator（对原版进行扩展）
        public class MyFutureValidator implements HibernateConstraintValidator<MyFuture, Instant> {
    private Clock clock;
    private boolean orPresent;
    @Override
    public void initialize(ConstraintDescriptor<MyFuture> constraintDescriptor,
            HibernateConstraintValidatorInitializationContext initializationContext) {
        this.orPresent = constraintDescriptor.getAnnotation().orPresent();
        this.clock = initializationContext.getClockProvider().getClock();
    }
    @Override
    public boolean isValid(Instant instant, ConstraintValidatorContext constraintContext) {
        //...
        return false;
    }
}

        将有效负载传递给约束验证器

        - 在ValidatorFactory初始化期间定义约束验证器有效载荷

        ValidatorFactory validatorFactory = Validation.byProvider( HibernateValidator.class )
        .configure()
        .constraintValidatorPayload( "US" )
        .buildValidatorFactory();
Validator validator = validatorFactory.getValidator();
        • 使用Validator上下文定义约束验证器有效载荷
        HibernateValidatorFactory hibernateValidatorFactory = Validation.byDefaultProvider()
        .configure()
        .buildValidatorFactory()
        .unwrap( HibernateValidatorFactory.class );
Validator validator = hibernateValidatorFactory.usingContext()
        .constraintValidatorPayload( "US" )
        .getValidator();
// [...] US specific validation checks
validator = hibernateValidatorFactory.usingContext()
        .constraintValidatorPayload( "FR" )
        .getValidator();
// [...] France specific validation checks
        • 在约束验证器中使用约束验证器有效载荷
        public class ZipCodeValidator implements ConstraintValidator<ZipCode, String> {
    public String countryCode;
    @Override
    public boolean isValid(String object, ConstraintValidatorContext constraintContext) {
        if ( object == null ) {
            return true;
        }
        boolean isValid = false;
        String countryCode = constraintContext
                .unwrap( HibernateConstraintValidatorContext.class )
                .getConstraintValidatorPayload( String.class );
        if ( "US".equals( countryCode ) ) {
            // checks specific to the United States
        }
        else if ( "FR".equals( countryCode ) ) {
            // checks specific to France
        }
        else {
            // ...
        }
        return isValid;
    }
}

        3. 错误讯息

        org.hibernate.validator.referenceguide.chapter06.CheckCase.message = 案例模式必须为{value}。

        4. 使用约束

        public class Car {
    @NotNull
    private String manufacturer;
    @NotNull
    @Size(min = 2, max = 14)
    @CheckCase(CaseMode.UPPER)
    private String licensePlate;
    @Min(2)
    private int seatCount;
    public Car(String manufacturer, String licencePlate, int seatCount) {
        this.manufacturer = manufacturer;
        this.licensePlate = licencePlate;
        this.seatCount = seatCount;
    }
    //getters and setters ...
}
        • 使用约束验证对象
        //invalid license plate
Car car = new Car( "Morris", "dd-ab-123", 4 );
Set<ConstraintViolation<Car>> constraintViolations =
        validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals(
        "Case mode must be UPPER.",
        constraintViolations.iterator().next().getMessage()
);
//valid license plate
car = new Car( "Morris", "DD-AB-123", 4 );
constraintViolations = validator.validate( car );
assertEquals( 0, constraintViolations.size() );

        二、类级别约束

        • 实现一个类级别约束
        @Target({ TYPE, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Constraint(validatedBy = { ValidPassengerCountValidator.class })
@Documented
public @interface ValidPassengerCount {
    String message() default "{org.hibernate.validator.referenceguide.chapter06.classlevel." +
            "ValidPassengerCount.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}

        public class ValidPassengerCountValidator
        implements ConstraintValidator<ValidPassengerCount, Car> {
    @Override
    public void initialize(ValidPassengerCount constraintAnnotation) {
    }
    @Override
    public boolean isValid(Car car, ConstraintValidatorContext context) {
        if ( car == null ) {
            return true;
        }
        return car.getPassengers().size() <= car.getSeatCount();
    }
}

        自定义属性路径

        public class ValidPassengerCountValidator
        implements ConstraintValidator<ValidPassengerCount, Car> {
    @Override
    public void initialize(ValidPassengerCount constraintAnnotation) {
    }
    @Override
    public boolean isValid(Car car, ConstraintValidatorContext constraintValidatorContext) {
        if ( car == null ) {
            return true;
        }
        boolean isValid = car.getPassengers().size() <= car.getSeatCount();
        if ( !isValid ) {
            constraintValidatorContext.disableDefaultConstraintViolation();
            constraintValidatorContext
                    .buildConstraintViolationWithTemplate( "{my.custom.template}" )
                    .addPropertyNode( "passengers" ).addConstraintViolation();
        }
        return isValid;
    }
}

        三、交叉级别约束

        • 交叉级别约束
        @Constraint(validatedBy = ConsistentDateParametersValidator.class)
@Target({ METHOD, CONSTRUCTOR, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Documented
public @interface ConsistentDateParameters {
    String message() default "{org.hibernate.validator.referenceguide.chapter04." +
            "crossparameter.ConsistentDateParameters.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}
        • 通用和交叉级别约束
        @SupportedValidationTarget(ValidationTarget.PARAMETERS)
public class ConsistentDateParametersValidator implements
        ConstraintValidator<ConsistentDateParameters, Object[]> {
    @Override
    public void initialize(ConsistentDateParameters constraintAnnotation) {
    }
    @Override
    public boolean isValid(Object[] value, ConstraintValidatorContext context) {
        if ( value.length != 2 ) {
            throw new IllegalArgumentException( "Illegal method signature" );
        }
        //leave null-checking to @NotNull on individual parameters
        if ( value[0] == null || value[1] == null ) {
            return true;
        }
        if ( !( value[0] instanceof Date ) || !( value[1] instanceof Date ) ) {
            throw new IllegalArgumentException(
                    "Illegal method signature, expected two " +
                            "parameters of type Date."
            );
        }
        return ( (Date) value[0] ).before( (Date) value[1] );
    }
}

        @Constraint(validatedBy = {
        ScriptAssertObjectValidator.class,
        ScriptAssertParametersValidator.class
})
@Target({ TYPE, FIELD, PARAMETER, METHOD, CONSTRUCTOR, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Documented
public @interface ScriptAssert {
    String message() default "{org.hibernate.validator.referenceguide.chapter04." +
            "crossparameter.ScriptAssert.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
    String script();
    ConstraintTarget validationAppliesTo() default ConstraintTarget.IMPLICIT;
}
        • 指定通用和交叉参数约束的目标
        @ScriptAssert(script = "arg1.size() <= arg0", validationAppliesTo = ConstraintTarget.PARAMETERS)
public Car buildCar(int seatCount, List<Passenger> passengers) {
    //...
    return null;
}

        四、约束构成

        • 创建一个合成约束 @ValidLicensePlate
        @NotNull
@Size(min = 2, max = 14)
@CheckCase(CaseMode.UPPER)
@Target({ METHOD, FIELD, ANNOTATION_TYPE, TYPE_USE })
@Retention(RUNTIME)
@Constraint(validatedBy = { })
@Documented
public @interface ValidLicensePlate {
    String message() default "{org.hibernate.validator.referenceguide.chapter06." +
            "constraintcomposition.ValidLicensePlate.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}
        • 组合约束的应用 ValidLicensePlate
        public class Car {
    @ValidLicensePlate
    private String licensePlate;
    //...
}
        • 使用@ReportAsSingleViolation
        @ReportAsSingleViolation
public @interface ValidLicensePlate {
    String message() default "{org.hibernate.validator.referenceguide.chapter06." +
            "constraintcomposition.reportassingle.ValidLicensePlate.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}
```ayload() default { };
}
        最后更新于 August 26, 2023
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