Spring自定义注解详解
下面是RequestBody注解源码
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestBody { /**
* Whether body content is required.
* <p>Default is {@code true}, leading to an exception thrown in case
* there is no body content. Switch this to {@code false} if you prefer
* {@code null} to be passed when the body content is {@code null}.
* @since 3.2
*/
boolean required() default true;
}现在讲一讲@RequestBody注解中用到其它注解
@Target注解
从字面上理解这个就是目标的意思，说明@RequestBody注解是作用于哪个上面
ElementType
public enum ElementType {
/** Class, interface (including annotation type), or enum declaration */
TYPE, /** Field declaration (includes enum constants) */
FIELD, /** Method declaration */
METHOD, /** Formal parameter declaration */
PARAMETER, /** Constructor declaration */
CONSTRUCTOR, /** Local variable declaration */
LOCAL_VARIABLE, /** Annotation type declaration */
ANNOTATION_TYPE, /** Package declaration */
PACKAGE, /**
* Type parameter declaration
*
* @since 1.8
*/
TYPE_PARAMETER, /**
* Use of a type
*
* @since 1.8
*/
TYPE_USE
}它的值有下列
| 值 | 说明(适用范围) |
|---|---|
| TYPE | 类，接口(包括注解类型)，枚举 |
| FIELD | 字段 |
| METHOD | 方法 |
| PARAMETER | 参数 |
| CONSTRUCTOR | 构造方法 |
| LOCAL_VARIABLE | 局部变量 |
| ANNOTATION_TYPE | 注解类型 |
| PACKAGE | 包 |
| TYPE_PARAMETER | 类型参数，从1.8开始 |
| TYPE_USE | 类型的使用，从1.8开始 |
@Retention注解
从字面上理解这个就是保留的意思，说明@RequestBody注解是在哪些环境下保留此注解
RetentionPolicy
public enum RetentionPolicy { /**
* Annotations are to be discarded by the compiler.
*/
SOURCE, /**
* Annotations are to be recorded in the class file by the compiler
* but need not be retained by the VM at run time. This is the default
* behavior.
*/
CLASS, /**
* Annotations are to be recorded in the class file by the compiler and
* retained by the VM at run time, so they may be read reflectively.
*
* @see java.lang.reflect.AnnotatedElement
*/
RUNTIME
}SOURCE 在编译时不保留此注解，此注解存在源代码中|
CLASS 在编译时保留注解于class文件中，VM运行时不需要保留，此值为默认值|
RUNTIME 在编译时保留注解于class文件中，VM运行时保留此注解，所以它们可以被反射阅读|
@Documented注解
此注解说明，如果生成javadoc文档时，会将该注解加入到文档中。
