Spring MVC Custom Validator

spring-mvc-java/src/main/java/com/baeldung/customvalidator/ContactNumberConstraint.java

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+package com.baeldung.customvalidator;
+
+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;
+
+@Documented
+@Constraint(validatedBy = ContactNumberValidator.class)
+@Target( { ElementType.METHOD, ElementType.FIELD })
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ContactNumberConstraint {
+
+    String message() default "Invalid phone number";
+    Class<?>[] groups() default {};
+    Class<? extends Payload>[] payload() default {};
+    
+}

spring-mvc-java/src/main/java/com/baeldung/customvalidator/ContactNumberValidator.java

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+package com.baeldung.customvalidator;
+
+import javax.validation.ConstraintValidator;
+import javax.validation.ConstraintValidatorContext;
+
+public class ContactNumberValidator implements ConstraintValidator<ContactNumberConstraint, String> {
+
+    @Override
+    public void initialize(ContactNumberConstraint contactNumber) {}
+
+    @Override
+    public boolean isValid(String contactField, ConstraintValidatorContext cxt) {
+        if(contactField == null) {
+            return false;
+        }
+        return contactField.matches("[0-9]+") && (contactField.length() > 8) && (contactField.length() < 14);        
+    }
+
+}