Java 声明注解

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 "";

}