Declarative XML-based Caching

如果注释不是一种选择（可能是因为无法访问源或外部代码），您可以使用 XML 进行声明性缓存。因此，您可以指定目标方法和外部缓存指令（类似于声明性事务管理advice），而无需为缓存注释方法。上一节的示例可以转换为以下示例：

If annotations are not an option (perhaps due to having no access to the sources or no external code), you can use XML for declarative caching. So, instead of annotating the methods for caching, you can specify the target method and the caching directives externally (similar to the declarative transaction management advice). The example from the previous section can be translated into the following example:

<!-- the service we want to make cacheable -->
<bean id="bookService" class="x.y.service.DefaultBookService"/>

<!-- cache definitions -->
<cache:advice id="cacheAdvice" cache-manager="cacheManager">
	<cache:caching cache="books">
		<cache:cacheable method="findBook" key="#isbn"/>
		<cache:cache-evict method="loadBooks" all-entries="true"/>
	</cache:caching>
</cache:advice>

<!-- apply the cacheable behavior to all BookService interfaces -->
<aop:config>
	<aop:advisor advice-ref="cacheAdvice" pointcut="execution(* x.y.BookService.*(..))"/>
</aop:config>

<!-- cache manager definition omitted -->

在前面的配置中，bookService 被设置为可缓存。要应用的缓存语义封装在 cache:advice 定义中，该定义导致 findBooks 方法用于将数据放入缓存，而 loadBooks 方法用于删除数据。这两个定义都针对 books 缓存进行操作。

In the preceding configuration, the bookService is made cacheable. The caching semantics to apply are encapsulated in the cache:advice definition, which causes the findBooks method to be used for putting data into the cache and the loadBooks method for evicting data. Both definitions work against the books cache.

通过使用 AspectJ 切点表达式（更多信息可在Aspect Oriented Programming with Spring中找到），`aop:config`定义将缓存建议应用到程序中的适当点。在前面的示例中，将会考虑 `BookService`中的所有方法并将缓存建议应用于它们。

The aop:config definition applies the cache advice to the appropriate points in the program by using the AspectJ pointcut expression (more information is available in Aspect Oriented Programming with Spring). In the preceding example, all methods from the BookService are considered and the cache advice is applied to them.

声明性 XML 缓存支持所有基于注释的模型，因此在两者之间移动应该相当容易。此外，两者都可以用在同一个应用程序中。基于 XML 的方法不会影响目标代码。但是，它本质上更加冗长。在处理针对缓存的超载方法的类时，识别正确的方法需要额外的努力，因为 method 参数不是一个好鉴别器。在这些情况下，您可以使用 AspectJ 切入点来选择目标方法并应用适当的缓存功能。但是，通过 XML，可以更容易地应用包或组或接口范围的缓存（同样，由于 AspectJ 切入点），并创建类似模板的定义（就像我们在前面的示例中通过 cache:definitions``cache 属性定义目标缓存所做的那样）。

The declarative XML caching supports all of the annotation-based model, so moving between the two should be fairly easy. Furthermore, both can be used inside the same application. The XML-based approach does not touch the target code. However, it is inherently more verbose. When dealing with classes that have overloaded methods that are targeted for caching, identifying the proper methods does take an extra effort, since the method argument is not a good discriminator. In these cases, you can use the AspectJ pointcut to cherry pick the target methods and apply the appropriate caching functionality. However, through XML, it is easier to apply package or group or interface-wide caching (again, due to the AspectJ pointcut) and to create template-like definitions (as we did in the preceding example by defining the target cache through the cache:definitions cache attribute).