001/*
002 * Copyright 2002-2019 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.lang;
018
019import java.lang.annotation.Documented;
020import java.lang.annotation.ElementType;
021import java.lang.annotation.Retention;
022import java.lang.annotation.RetentionPolicy;
023import java.lang.annotation.Target;
024
025import javax.annotation.Nonnull;
026import javax.annotation.meta.TypeQualifierNickname;
027import javax.annotation.meta.When;
028
029/**
030 * A common Spring annotation to declare that annotated elements can be {@code null} under
031 * some circumstance.
032 *
033 * <p>Leverages JSR-305 meta-annotations to indicate nullability in Java to common
034 * tools with JSR-305 support and used by Kotlin to infer nullability of Spring API.
035 *
036 * <p>Should be used at parameter, return value, and field level. Methods override should
037 * repeat parent {@code @Nullable} annotations unless they behave differently.
038 *
039 * <p>Can be used in association with {@code @NonNullApi} or {@code @NonNullFields} to
040 * override the default non-nullable semantic to nullable.
041 *
042 * @author Sebastien Deleuze
043 * @author Juergen Hoeller
044 * @since 5.0
045 * @see NonNullApi
046 * @see NonNullFields
047 * @see NonNull
048 */
049@Target({ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD})
050@Retention(RetentionPolicy.RUNTIME)
051@Documented
052@Nonnull(when = When.MAYBE)
053@TypeQualifierNickname
054public @interface Nullable {
055}