Add PowerOfTwo validator

src/main/java/io/airlift/units/PowerOfTwo.java

@@ -0,0 +1,38 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.airlift.units;
+
+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.ANNOTATION_TYPE;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+@Target({METHOD, ANNOTATION_TYPE})
+@Retention(RUNTIME)
+@Documented
+@Constraint(validatedBy = PowerOfTwoValidator.class)
+public @interface PowerOfTwo
+{
+    String message() default "is not a power of two";
+
+    Class<?>[] groups() default {};
+
+    Class<? extends Payload>[] payload() default {};
+}

src/main/java/io/airlift/units/PowerOfTwoValidator.java

@@ -0,0 +1,32 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.airlift.units;
+
+import javax.validation.ConstraintValidator;
+import javax.validation.ConstraintValidatorContext;
+
+public class PowerOfTwoValidator
+        implements ConstraintValidator<PowerOfTwo, Integer>
+{
+    @Override
+    public void initialize(PowerOfTwo powerOfTwo)
+    {
+    }
+
+    @Override
+    public boolean isValid(Integer value, ConstraintValidatorContext context)
+    {
+        return value == null || Integer.bitCount(value) == 1;
+    }
+}