java自定义注解

定义一个简单的注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface DataReplicationParam {

    String value();
}

注解说明

1.@target描述应用范围
ElementType元素类型，元素含义自行翻译注释即可

下面为源码

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
}

2.@Retention作用修饰注解，RetentionPolicy属性保留注解

下面为源码

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
}

3.@Inherited注解 @Documented注解
@Inherited注解用于标注一个父类的注解是否可以被子类继承，如果一个注解需要被其子类所继承，则在声明时直接使用@Inherited注解即可。如果没有写此注解，则无法被子类继承。
@Documented注解将自定义注解设置为文档说明内容，在生成javadoc时会将该注解加入到文档中。

学习地址：https://blog.youkuaiyun.com/chengqiuming/article/details/81606585