深入理解注解与自定义注解的一些概念

@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Autowired {
    boolean required() default true;
}

public enum ElementType {
    /** 类，接口（包括注解类型）或枚举的声明 */
    TYPE,
 
    /** 属性的声明 */
    FIELD,
 
    /** 方法的声明 */
    METHOD,
 
    /** 方法形式参数声明 */
    PARAMETER,
 
    /** 构造方法的声明 */
    CONSTRUCTOR,
 
    /** 局部变量声明 */
    LOCAL_VARIABLE,
 
    /** 注解类型声明 */
    ANNOTATION_TYPE,
 
    /** 包的声明 */
    PACKAGE
}

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     * 注释将被编译器丢弃
     */
    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.
     * 编译器将注释记录在类文件中，但不需要在运行时被VM保留。这是默认值
     */
    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.
     * 编译器将注释记录在类文件中，在运行时由VM保留，因此它们可能被反射地读取
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EnumValid {
    /**
     * fieldName
     * @return 
     */
    String name() default "fieldName";
    // 注解类型变量...
}

public class ReqDTO {
    @EnumValid(name = "typeName")
    private String typeName;
}