001/*
002 * Copyright 2002-2015 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.messaging.handler.annotation;
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 org.springframework.core.annotation.AliasFor;
026import org.springframework.messaging.converter.MessageConverter;
027
028/**
029 * Annotation that binds a method parameter to the payload of a message. Can also
030 * be used to associate a payload to a method invocation. The payload may be passed
031 * through a {@link MessageConverter} to convert it from serialized form with a
032 * specific MIME type to an Object matching the target method parameter.
033 *
034 * @author Rossen Stoyanchev
035 * @author Sam Brannen
036 * @since 4.0
037 */
038@Target({ElementType.PARAMETER, ElementType.METHOD})
039@Retention(RetentionPolicy.RUNTIME)
040@Documented
041public @interface Payload {
042
043        /**
044         * Alias for {@link #expression}.
045         */
046        @AliasFor("expression")
047        String value() default "";
048
049        /**
050         * A SpEL expression to be evaluated against the payload object as the root context.
051         * <p>This attribute may or may not be supported depending on whether the message being
052         * handled contains a non-primitive Object as its payload or is in serialized form and
053         * requires message conversion.
054         * <p>When processing STOMP over WebSocket messages this attribute is not supported.
055         * @since 4.2
056         */
057        @AliasFor("value")
058        String expression() default "";
059
060        /**
061         * Whether payload content is required.
062         * <p>Default is {@code true}, leading to an exception if there is no payload. Switch
063         * to {@code false} to have {@code null} passed when there is no payload.
064         */
065        boolean required() default true;
066
067}