How to write custom annotations?

Custom check

 1）、编写一个自定义的校验注解

 2）、编写一个自定义的校验器 ConstraintValidator

 3）、关联自定义的校验器和自定义的校验注解

How to write validation annotations, we can refer to @NotBlank in JSR303:
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He has three attributes:

//校验出错后,去此路径下去拿去错误信息,
String message() default "{javax.validation.constraints.NotBlank.message}";

//支持分组检验功能
Class<?>[] groups() default {
    
     };

//负载信息
Class<? extends Payload>[] payload() default {
    
     };

Therefore, we first need to copy these three pieces of information (we name our own verification class ListValue):
Of course, we also need to copy these 5 notes.

@Documented
//该校验注解使用那个校验器进行校验
@Constraint(validatedBy = {
    
     })
//此注解可以标注在哪些位置
@Target({
    
     METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
//校验注解的时机
@Retention(RUNTIME)
//可重复注解可不要
@Repeatable(List.class)

But these annotations are in the javax.validation package, so they must be introduced in maven first:

<dependency>
     <groupId>javax.validation</groupId>
     <artifactId>validation-api</artifactId>
     <version>2.0.1.Final</version>
</dependency>

3. Because JSR303 obtains the error information in the ValidationMessages.properties file by default, if we modify the path, we must create a new ValidationMessages.properties file by
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ourselves. For example, my ListValue is written!

import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

@Documented
@Constraint(validatedBy = {
    
    ListValueConstraintValidator.class})
@Target({
    
     METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
public @interface ListValue {
    
    
    String message() default "{com.atguigu.common.valid.ListValue.message.message}";

    Class<?>[] groups() default {
    
     };

    Class<? extends Payload>[] payload() default {
    
     };
    int[] vals() default {
    
     };
}

Next, we need to specify which validator to use to validate the annotation. Same as above, we can look at the implementation of validatedBy:
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that is, we need to specify an array of type ConstraintValidator, and then, we are looking at the implementation of ConstraintValidator,

you can see that it is an excuse ConstraintValidator <A extends Annotation, T>, first specify the generic annotation, second generic designated check what type of data , so we only need to write a check to implement this method is the interface can be!
less Is my validator:

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import java.util.HashSet;
import java.util.Set;

public class ListValueConstraintValidator implements ConstraintValidator<ListValue, Integer> {
    
    
    private Set<Integer> set = new HashSet<>();
    @Override
    public void initialize(ListValue constraintAnnotation) {
    
    
    	//拿到我们注解的Vals的值0,1,
        int[] vals = constraintAnnotation.vals();
        for (int val : vals) {
    
    
            set.add(val);
        }
    }
    //判断是否检验成功!

    /**
     *
     * @param value  我们提交的值(需要校验的值
     * @param context,上下文环境信息
     * @return
     */
    @Override
    public boolean isValid(Integer value, ConstraintValidatorContext context) {
    
    
        return set.contains(value);
    }
}

At this point, my ListValue can be used normally.
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When we submit a request with postMan:

showStatus is the same as the information in the ValidationMessages.properties we wrote. Of course, we can also change the prompt information through Messenge.

How to write custom annotations?

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