注解其实可以看成是一个特殊的 Class 。 只不过不用关键字 class 而已， 而是用 声明
@Target 说明注解使用的地方(目的地) {类上，字段上，或是方法上？？ etc... }。
类上面：TYPE
字段上：FIELD
方法上：METHOD
@Retention 注解的生存周期(能在什么时候有效) 可选值为：源代码 ？ 一直到运行时都有效 ？etc...
RUNTIME 一直到运行时都有效，说明程序运行时可以通过反射得到注解的信息。
@Target({TYPE, FIELD, METHOD})
@Retention(RUNTIME)
public @interface Resource {
/**
* The JNDI name of the resource. For field annotations,
* the default is the field name. For method annotations,
* the default is the JavaBeans property name corresponding
* to the method. For class annotations, there is no default
* and this must be specified.
*/
String name() default "";
/**
* The Java type of the resource. For field annotations,
* the default is the type of the field. For method annotations,
* the default is the type of the JavaBeans property.
* For class annotations, there is no default and this must be
* specified.
*/
Class type() default java.lang.Object.class;
/**
* The two possible authentication types for a resource.
*/
enum AuthenticationType {
CONTAINER,
APPLICATION
}
/**
* The authentication type to use for this resource.
* This may be specified for resources representing a
* connection factory of any supported type, and must
* not be specified for resources of other types.
*/
AuthenticationType authenticationType() default AuthenticationType.CONTAINER;
/**
* Indicates whether this resource can be shared between
* this component and other components.
* This may be specified for resources representing a
* connection factory of any supported type, and must
* not be specified for resources of other types.
*/
boolean shareable() default true;
/**
* A product specific name that this resource should be mapped to.
* The name of this resource, as defined by the <code>name</code>
* element or defaulted, is a name that is local to the application
* component using the resource. (It's a name in the JNDI
* <code>java:comp/env</code> namespace.) Many application servers
* provide a way to map these local names to names of resources
* known to the application server. This mapped name is often a
* <i>global</i> JNDI name, but may be a name of any form. <p>
*
* Application servers are not required to support any particular
* form or type of mapped name, nor the ability to use mapped names.
* The mapped name is product-dependent and often installation-dependent.
* No use of a mapped name is portable.
*/
String mappedName() default "";
/**
* Description of this resource. The description is expected
* to be in the default language of the system on which the
* application is deployed. The description can be presented
* to the Deployer to help in choosing the correct resource.
*/
String description() default "";
}
