Java™ JSR-107 缓存API：最终规范

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"JSR-107 文档是 Java 缓存 API 的官方规范，由 JSR107 专家小组制定，旨在提供一个标准接口，让 Java 程序员能够与各种缓存系统进行交互。文档的主要作者包括 Greg Luck 和 Brian Oliver（来自 Oracle Corporation）。该文档的版本为 1.0，最终发布于2013年12月16日，遵循特定的许可证协议，下载和使用需同意其条款。" JSR-107，也被称为 JCache，是 Java Temporary Caching API 的简称，它为 Java 平台引入了一个标准的缓存接口，以提高应用程序的性能和效率。缓存是一种常见的软件设计模式，用于临时存储经常访问的数据，减少对持久性存储或计算资源的访问，从而提高系统的响应速度。 **核心概念：** 1. **Cache**: 缓存对象，用于存储键值对。它是缓存操作的主要接口，提供了添加、获取、删除和更新缓存项的方法。 2. **Key**: 缓存项的键，通常是一个对象，用于唯一标识缓存中的数据。 3. **Value**: 缓存项的值，是与键关联的数据。 4. **Expiry Policy**: 过期策略，定义了缓存项何时应该被视为过期并从缓存中移除。可以基于时间、访问频率或写入频率来设置。 5. **Eviction Policy**: 淘汰策略，当缓存达到其容量限制时，决定哪些项应被从缓存中移除。 6. **Cache Manager**: 缓存管理器，负责创建、配置和管理多个缓存实例。 **关键特性：** 1. **分布式缓存支持**: JSR-107 提供了在多节点环境中分布缓存的能力，以实现高可用性和可扩展性。 2. **事件监听器**: 允许注册监听器来响应缓存项的添加、修改和移除事件，以便进行相应的业务逻辑处理。 3. **异步操作**: 支持异步缓存操作，提高性能并允许非阻塞处理。 4. **缓存绑定**: 可以将缓存与其他框架（如 Spring 或 CDI）集成，方便地在应用中使用。 5. **缓存配置**: 提供了一种标准的方式来配置缓存的属性，如容量、过期时间等。 **使用场景：** - 数据库连接池：缓存数据库连接，减少创建和销毁连接的开销。 - 计算结果：保存昂贵计算的结果，避免重复计算。 - 静态内容：缓存静态网页内容，快速响应用户请求。 - 分布式系统中的状态共享：在分布式服务之间共享状态信息。 JSR-107 的实施库，如 Ehcache 和 Infinispan，允许开发者根据需求选择适合的缓存解决方案。通过遵循 JSR-107 规范，开发者可以编写与缓存实现无关的代码，确保代码的可移植性和互操作性。

Java

Caching API – Final

&G"

invokeAll(Set<? extends K> keys,

EntryProcessor<K, V, T> entryProcessor,

Object... arguments);

happen-before for each key individually but not

for the Collection.

boolean replace(K key, V value)

happen-before plus compare and swap

boolean replace(K key, V oldValue, V

newValue)

happen-before plus compare and swap

<T> T unwrap(Class<T> cls)

N/A

2.3.2. Further Consistency Models

An implementation may provide support for different consistency models in addition to the required

Default Consistency model.

2.4. Cache Topologies

While the specification does not mandate particular cache topologies, it is cognizant that Cache

entries may well be stored locally and/or distributed across multiple processes. Implementation may

choose to support neither, one, both and/or other topologies.

This notion is expressed in the specification in a number of ways:

● Most mutating methods provide a signature with a void or low cost return types. For example,

while java.util.Map provides the method V put(K key, V value)

javax.cache.Cache provide void put(K key, V value).

Versions with a more expensive return type are also provided. An example is the V

getAndPut(K key, V value) method on Cache. It returns the old value like Map does.

● By having creation semantics that do not assume in-process implementation, Configuration

is Serializable so that it can be sent over the network. Developers may define

implementations of CacheEntryListener, ExpiryPolicy, CacheEntryFilter,

CacheWriter and CacheLoader and associate them with a cache. To support distributed

topologies, a developer defines a Factory for their creation rather than the instance. The

Factory interface is Serializable.

● The use of Iterable throughout the specification for return types and parameters that might be

large.

Methods that return an entire collection such as the Map method keySet() can be

problematic.

A Cache may be so large that a key set may not fit in available memory and it might also be

Java

Caching API – Final

&1"

very network inefficient.

Cache, the listener methods on CacheEntryListener’s subinterfaces, and the batch

methods on CacheLoader all use Iterable.

● No assumption is made as to where implementations of CacheEntryListener,

ExpiryPolicy, CacheEntryFilter, CacheWriter and CacheLoader are instantiated

and executed.

In a distributed implementation these may all reside close to the data rather than in process

with the application.

● CachingProvider.getCacheManager(URI uri, ClassLoader classLoader) returns

a CacheManager with a specific ClassLoader and URI. This enables implementations to

instantiate multiple instances.

2.5. Execution Context

EntryProcessors, CacheEntryListeners, CacheLoaders, CacheWriters and

ExpiryPolicys (“customizations”) are instantiated and operate in the context of the CacheManager

URI and ClassLoader in which they were configured. This means at deployment time, instances of

these customizations must be available to and have access to application classes defined by the

ClassLoader for a Cache.

Implementations may safely assume such customizations are available to a Cache using the

ClassLoader as provided by a CacheManager.

How the availability of classes is achieved is implementation and deployment dependent.

For example: In a Java EE environment, application defined Customizations may be deployed within

the scope of an enterprise application ear/war/jar.

While customizations may be available in the same ClassLoader as an application and thus have

access to all application classes, to ensure portability application customizations must avoid direct

access to deployment specific resources. Instead customizations should only attempt to access and

mutate the Cache information and entries provided to them.

In implementations and deployment environments that support it, customizations may additionally

utilize technologies such as resource injection (e.g: CDI) to allow direct access to application and

deployment specific resources. There is no requirement however that implementations support this

ability.

2.6. Reentrancy

While this specification does not constrain the operations a developer may perform when using

custom EntryProcessors, CacheEntryListeners, CacheLoaders, CacheWriters and

ExpiryPolicys, caching implementations may restrict reentrancy from these interfaces. For

example; an implementation may restrict the ability for an EntryProcessor to call methods on

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