深入理解spring注解的构成

自定义注解

public @interface zhujie {
}

其实最简单注解就是这样的，直接使用@interface后面跟上你想自定义的注解的名字即可

当然了，有一些本身在注解上常用的注解，下面一一来介绍。

原生注解

@target

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Target {
    /**
     * Returns an array of the kinds of elements an annotation type
     * can be applied to.
     * @return an array of the kinds of elements an annotation type
     * can be applied to
     */
    ElementType[] value();
}

elementpye

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    //类，接口或者枚举类
    TYPE,

    /** Field declaration (includes enum constants) */
    //变量声明
    FIELD,

    /** Method declaration */
    //方法声明
    METHOD,

    /** Formal parameter declaration */
    //格式化声明
    PARAMETER,

    /** Constructor declaration */
    //构造声明
    CONSTRUCTOR,

    /** Local variable declaration */
    //本地变量声明
    LOCAL_VARIABLE,

    /** Annotation type declaration */
    //注解类型声明
    ANNOTATION_TYPE,

    /** Package declaration */
    //打包
    PACKAGE,

    /**
     * Type parameter declaration
     *
     * @since 1.8
     */
    TYPE_PARAMETER,

    /**
     * Use of a type
     *
     * @since 1.8
     */
    //用户类型
    TYPE_USE
}

@Retention

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Retention {
    /**
     * Returns the retention policy.
     * @return the retention policy
     */
    RetentionPolicy value();
}

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     * 批注将被编译器丢弃
     */
    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.
     *注释将由编译器记录在类文件中，但VM不必在运行时保留它们。 这是默认行为。
     */
    //
    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.
     *注释将由编译器记录在类文件中，并在运行时由VM保留，因此可以通过反射方式读取它们。
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

@Documented

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Documented {
}