緩存工具
緩存設計
緩存接口
/**
* Copyright 2009-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.ibatis.cache;
import java.util.concurrent.locks.ReadWriteLock;
/**
* SPI for cache providers.
*
* One instance of cache will be created for each namespace.
*
* The cache implementation must have a constructor that receives the cache id as an String parameter.
*
* MyBatis will pass the namespace as id to the constructor.
*
* <pre>
* public MyCache(final String id) {
* if (id == null) {
* throw new IllegalArgumentException("Cache instances require an ID");
* }
* this.id = id;
* initialize();
* }
* </pre>
*
* @author Clinton Begin
*/
public interface Cache {
/**
* @return The identifier of this cache
*/
String getId();
/**
* @param key Can be any object but usually it is a {@link CacheKey}
* @param value The result of a select.
*/
void putObject(Object key, Object value);
/**
* @param key The key
* @return The object stored in the cache.
*/
Object getObject(Object key);
/**
* As of 3.3.0 this method is only called during a rollback
* for any previous value that was missing in the cache.
* This lets any blocking cache to release the lock that
* may have previously put on the key.
* A blocking cache puts a lock when a value is null
* and releases it when the value is back again.
* This way other threads will wait for the value to be
* available instead of hitting the database.
*
*
* @param key The key
* @return Not used
*/
Object removeObject(Object key);
/**
* Clears this cache instance
*/
void clear();
/**
* Optional. This method is not called by the core.
*
* @return The number of elements stored in the cache (not its capacity).
*/
int getSize();
/**
* Optional. As of 3.2.6 this method is no longer called by the core.
*
* Any locking needed by the cache must be provided internally by the cache provider.
*
* @return A ReadWriteLock
*/
ReadWriteLock getReadWriteLock();
}
我們來討論一下，說到MyBatis，我們的第一印象是什么？毫無疑問是數據庫交互操作，那么問題來了，如果要用到緩存怎么辦？還好MyBatis也是支持。
俗話說的好，一個人只會在一方面精通，不可能都做得好，那有人是專門做緩存的，怎么去獲取數據呢？
MyBatis就提供了這樣一個Cache接口。誰做得好，誰就去實現就行了。
都知道Spring強大，面試的時候，都會問，那么我們為什么要用Spring呢？我們在用的時候，也感覺Spring好厲害，好像都在用。
Spring 需要集成很多別的框架，才能幫助我們完成整個系統，說白了，Spring就是一個容器。
所以我們在系統設計的時候，也可采取這樣的方式，把自己當做一個容器，先把需要的東西寫成接口，不管我自己能不能實現，這都不重要。
后記
下一節，我們來學習MyBatis的運行原理。
