diff --git a/pom.xml b/pom.xml
index fe714c6..2aab438 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,7 +6,7 @@
 
   <groupId>io.github.sashirestela</groupId>
   <artifactId>slimvalidator</artifactId>
-  <version>1.1.0</version>
+  <version>1.2.0</version>
   <packaging>jar</packaging>
 
   <name>slimvalidator</name>
@@ -52,16 +52,16 @@
     <maven.compiler.release>11</maven.compiler.release>
     <!-- Dependencies Versions -->
     <slf4j.version>2.0.12</slf4j.version>
-    <lombok.version>1.18.30</lombok.version>
+    <lombok.version>1.18.32</lombok.version>
     <junit.version>5.10.2</junit.version>
     <!-- Plugins Versions -->
-    <compiler.version>3.12.1</compiler.version>
+    <compiler.version>3.13.0</compiler.version>
     <enforcer.version>3.4.1</enforcer.version>
     <surefire.version>3.2.5</surefire.version>
     <exec.version>3.2.0</exec.version>
-    <jacoco.version>0.8.11</jacoco.version>
+    <jacoco.version>0.8.12</jacoco.version>
     <versions.version>2.16.2</versions.version>
-    <source.version>3.3.0</source.version>
+    <source.version>3.3.1</source.version>
     <javadoc.version>3.6.3</javadoc.version>
     <gpg.version>3.1.0</gpg.version>
     <sonatype.version>1.6.13</sonatype.version>
diff --git a/src/main/java/io/github/sashirestela/slimvalidator/constraints/Extension.java b/src/main/java/io/github/sashirestela/slimvalidator/constraints/Extension.java
new file mode 100644
index 0000000..6c86e00
--- /dev/null
+++ b/src/main/java/io/github/sashirestela/slimvalidator/constraints/Extension.java
@@ -0,0 +1,20 @@
+package io.github.sashirestela.slimvalidator.constraints;
+
+import io.github.sashirestela.slimvalidator.Constraint;
+import io.github.sashirestela.slimvalidator.validators.ExtensionValidator;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Constraint(validatedBy = ExtensionValidator.class)
+@Target({ ElementType.FIELD })
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Extension {
+
+    String message() default "extension must be one of {value}.";
+
+    String[] value();
+
+}
diff --git a/src/main/java/io/github/sashirestela/slimvalidator/util/Common.java b/src/main/java/io/github/sashirestela/slimvalidator/util/Common.java
index fc3083b..5bd2ea1 100644
--- a/src/main/java/io/github/sashirestela/slimvalidator/util/Common.java
+++ b/src/main/java/io/github/sashirestela/slimvalidator/util/Common.java
@@ -57,6 +57,9 @@ public static String toStringByAnnotMethodType(Object value) {
                 return value.toString();
             }
         }
+        if (value.getClass().isArray() && value.getClass().getComponentType().equals(String.class)) {
+            return Arrays.toString((String[]) value);
+        }
         return value.toString();
     }
 
diff --git a/src/main/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidator.java b/src/main/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidator.java
new file mode 100644
index 0000000..5b88596
--- /dev/null
+++ b/src/main/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidator.java
@@ -0,0 +1,42 @@
+package io.github.sashirestela.slimvalidator.validators;
+
+import io.github.sashirestela.slimvalidator.ConstraintValidator;
+import io.github.sashirestela.slimvalidator.constraints.Extension;
+import io.github.sashirestela.slimvalidator.exception.ValidationException;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.util.Arrays;
+
+/**
+ * Checks that the file extension is one of an expected list. Applies to {@link java.nio.file.Path
+ * Path} and {@link java.io.File File} objects.
+ */
+public class ExtensionValidator implements ConstraintValidator<Extension, Object> {
+
+    private String[] extensions;
+
+    @Override
+    public void initialize(Extension annotation) {
+        extensions = annotation.value();
+    }
+
+    @Override
+    public boolean isValid(Object value) {
+        if (value == null) {
+            return true;
+        }
+        return Arrays.stream(extensions).anyMatch(ext -> ext.equals(getExtension(value)));
+    }
+
+    private String getExtension(Object value) {
+        if (value instanceof Path) {
+            return ((Path) value).toString().split("\\.")[1];
+        } else if (value instanceof File) {
+            return ((File) value).getName().split("\\.")[1];
+        } else {
+            throw new ValidationException("Cannot get a extension from {0}.", value.getClass().getName(), null);
+        }
+    }
+
+}
diff --git a/src/main/java/io/github/sashirestela/slimvalidator/validators/RequiredValidator.java b/src/main/java/io/github/sashirestela/slimvalidator/validators/RequiredValidator.java
index 0d4284a..ad8a196 100644
--- a/src/main/java/io/github/sashirestela/slimvalidator/validators/RequiredValidator.java
+++ b/src/main/java/io/github/sashirestela/slimvalidator/validators/RequiredValidator.java
@@ -16,12 +16,7 @@ public boolean isValid(Object value) {
         if (value == null) {
             return false;
         } else {
-            var groupSize = getGroupSize(value);
-            if (groupSize == -1) {
-                return true;
-            } else {
-                return (groupSize > 0);
-            }
+            return getGroupSize(value) != 0;
         }
     }
 
diff --git a/src/test/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidatorTest.java b/src/test/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidatorTest.java
new file mode 100644
index 0000000..26b892d
--- /dev/null
+++ b/src/test/java/io/github/sashirestela/slimvalidator/validators/ExtensionValidatorTest.java
@@ -0,0 +1,88 @@
+package io.github.sashirestela.slimvalidator.validators;
+
+import io.github.sashirestela.slimvalidator.constraints.Extension;
+import io.github.sashirestela.slimvalidator.exception.ValidationException;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.lang.annotation.Annotation;
+import java.nio.file.Paths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class ExtensionValidatorTest {
+
+    String fileName = "src/test/resources/sample.txt";
+
+    @Test
+    void shouldReturnTrueWhenValidatingObjectAgainstAnnnotation() {
+        Object[][] data = {
+                { null, Sample.extension(null) },
+                { new File(fileName), Sample.extension(new String[] { "doc", "csv", "txt" }) },
+                { Paths.get(fileName), Sample.extension(new String[] { "doc", "csv", "txt" }) }
+        };
+        for (Object[] value : data) {
+            var validator = new ExtensionValidator();
+            var annotation = (Extension) value[1];
+            validator.initialize(annotation);
+            var actualResult = validator.isValid(value[0]);
+            var expectedResult = true;
+            assertEquals(expectedResult, actualResult);
+        }
+    }
+
+    @Test
+    void shouldReturnFalseWhenValidatingObjectAgainstAnnnotation() {
+        Object[][] data = {
+                { new File(fileName), Sample.extension(new String[] { "jpg", "gif", "bmp" }) },
+                { Paths.get(fileName), Sample.extension(new String[] { "jpg", "gif", "bmp" }) }
+        };
+        for (Object[] value : data) {
+            var validator = new ExtensionValidator();
+            var annotation = (Extension) value[1];
+            validator.initialize(annotation);
+            var actualResult = validator.isValid(value[0]);
+            var expectedResult = false;
+            assertEquals(expectedResult, actualResult);
+        }
+    }
+
+    @Test
+    void shouldThrownExceptionWhenNonExpectedObjectIsPassed() {
+        var validator = new ExtensionValidator();
+        var annotation = Sample.extension(new String[] { "mp3", "wav" });
+        validator.initialize(annotation);
+        var exception = assertThrows(ValidationException.class, () -> validator.isValid("filename.mp3"));
+        var actualMessage = exception.getMessage();
+        var expectedMessage = "Cannot get a extension from java.lang.String.";
+        assertEquals(expectedMessage, actualMessage);
+    }
+
+    static class Sample {
+
+        static Extension extension(String[] value) {
+            return new Extension() {
+
+                @Override
+                public Class<? extends Annotation> annotationType() {
+                    return Extension.class;
+                }
+
+                @Override
+                public String message() {
+                    return "";
+                }
+
+                @Override
+                public String[] value() {
+                    return value;
+                }
+
+            };
+
+        }
+
+    }
+
+}
diff --git a/src/test/resources/sample.txt b/src/test/resources/sample.txt
new file mode 100644
index 0000000..27b74e7
--- /dev/null
+++ b/src/test/resources/sample.txt
@@ -0,0 +1 @@
+This is a sample file for testing.