java自定义注解 @Pattern 为空字符串的时候，不需校验正则表达式

注解：BlankOrPattern.java

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.validation.Constraint;
import javax.validation.Payload;
import javax.validation.constraints.Pattern;
 
/**自定义注解
 * 验证器  当 当字段不为null且长度>0  才执行正则校验
 */
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.CONSTRUCTOR, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy = {BlankOrPatternValidator.class})
public @interface BlankOrPattern {
    String regexp();
 
    Pattern.Flag[] flags() default {};
 
    String message() default "{javax.validation.constraints.Pattern.message}";
 
    Class[] groups() default {};
 
    Class[] payload() default {};
 
    @Target({ElementType.METHOD, ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.CONSTRUCTOR, ElementType.PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface List {
        Pattern[] value();
    }
 
    public static enum Flag {
        UNIX_LINES(1),
        CASE_INSENSITIVE(2),
        COMMENTS(4),
        MULTILINE(8),
        DOTALL(32),
        UNICODE_CASE(64),
        CANON_EQ(128);
 
        private final int value;
 
        private Flag(int value) {
            this.value = value;
        }
 
        public int getValue() {
            return this.value;
        }
    }
}

验证器：BlankOrPatternValidator.java

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import javax.validation.constraints.Pattern.Flag;
import java.util.regex.Matcher;
import java.util.regex.PatternSyntaxException;
 
/**
 * 验证器  当字段不为null且长度>0  才执行正则校验
 */
public class BlankOrPatternValidator implements ConstraintValidator {
    private static final Log log = LoggerFactory.make();
    private java.util.regex.Pattern pattern;
 
    public BlankOrPatternValidator() {
    }
 
    @Override
    public void initialize(BlankOrPattern parameters) {
        Flag[] flags = parameters.flags();
        int intFlag = 0;
        Flag[] arr$ = flags;
        int len$ = flags.length;
 
        for(int i$ = 0; i$ < len$; ++i$) {
            Flag flag = arr$[i$];
            intFlag |= flag.getValue();
        }
 
        try {
            this.pattern = java.util.regex.Pattern.compile(parameters.regexp(), intFlag);
        } catch (PatternSyntaxException var8) {
            throw log.getInvalidRegularExpressionException(var8);
        }
    }
 
    @Override
    public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
        if (value == null ||value.length() == 0) {
            return true;
        } else {
            Matcher m = this.pattern.matcher(value);
            return m.matches();
        }
    }
}

参考 https://blog.csdn.net/qq_16909139/article/details/107056445