Payload (Spring Framework 5.2.12.RELEASE API)

```
@Target({PARAMETER,METHOD})
@Retention(RUNTIME)
@Documented
public @interface Payload
```
Annotation that binds a method parameter to the payload of a message. Can also be used to associate a payload to a method invocation. The payload may be passed through a MessageConverter to convert it from serialized form with a specific MIME type to an Object matching the target method parameter.
从以下版本开始:
4.0
作者:
Rossen Stoyanchev, Sam Brannen

可选元素概要

可选元素
修饰符和类型	可选元素	说明
`String`	`expression`	A SpEL expression to be evaluated against the payload object as the root context.
`boolean`	`required`	Whether payload content is required.
`String`	`value`	Alias for `expression()`.

- 元素详细资料
  - value
```
@AliasFor("expression")
String value
```
    Alias for expression().
    默认值:
    ""
- - expression
```
@AliasFor("value")
String expression
```
    A SpEL expression to be evaluated against the payload object as the root context.
    This attribute may or may not be supported depending on whether the message being handled contains a non-primitive Object as its payload or is in serialized form and requires message conversion.
    When processing STOMP over WebSocket messages this attribute is not supported.
    从以下版本开始:
    4.2
    默认值:
    ""
- - required
```
boolean required
```
    Whether payload content is required.
    Default is true, leading to an exception if there is no payload. Switch to false to have null passed when there is no payload.
    默认值:
    true