缓存初解（四）---Ibatis的缓存配置+Ehcache

项目完结，整理一些技术方面的相关收获。
已经记不得EhCacheController这个实现类最早来自于那里了，总之稍加修改后非常有效果，大家就这么用了，感谢最初开源的那位兄弟。这里，主要是做个记录，为以后类似扩展（譬如Memcached）做个准备。

iBatis提供CacheController接口，用于实现第三方缓存架构的扩展。

这里以iBatis 2.3.0，EhCache 1.2.3版本为基础，构建iBatis+EhCache实现。

EhCacheController类：

package com.ibatis.sqlmap.engine.cache.ehcache;

import java.net.URL;
import java.util.Properties;

import net.sf.ehcache.Cache;
import net.sf.ehcache.CacheManager;
import net.sf.ehcache.Element;

import com.ibatis.sqlmap.engine.cache.CacheController;
import com.ibatis.sqlmap.engine.cache.CacheModel;

/**
 * EhCache Implementation of the
 * {@link com.ibatis.sqlmap.engine.cache.CacheController} interface to be able
 * to use EhCache as a cache implementation in iBatis. You can configure your
 * cache model as follows, by example, in your sqlMapping files:
 *
 * <pre>
 * <code>
 * <cacheModel id="myCache" readOnly="true" serialize="false"
 * 	type="com.ibatis.sqlmap.engine.cache.EhCacheController" >
 * 	<property name="configLocation"
 * 		value="/path-to-ehcache.xml"/>
 * </cacheModel> </code>
 * </pre>
 *
 * Alternatively, you can use a type alias in your type attribute and defining
 * the class with a <code><typeAlias></code> declaration:
 *
 * <pre>
 * <code>
 * <sqlMapConfig>
 * 	<typeAlias alias="EHCACHE"
 * 		type="com.ibatis.sqlmap.engine.cache.ehcache.EhCacheController" />
 * </sqlMapConfig>
 * </code>
 * </pre>
 *
 */
public class EhCacheController implements CacheController {

	/**
	 * The EhCache CacheManager.
	 */
	private CacheManager cacheManager;

	public static final String CONFIG_LOCATION = "configLocation";

	/**
	 * Default Configure Location
	 */
	public static final String DEFAULT_CONFIG_LOCATION = "/ehcache.xml";

	/**
	 * Flush a cache model.
	 *
	 * @param cacheModel
	 *            - the model to flush.
	 */
	public void flush(CacheModel cacheModel) {
		getCache(cacheModel).removeAll();
	}

	/**
	 * Get an object from a cache model.
	 *
	 * @param cacheModel
	 *            - the model.
	 * @param key
	 *            - the key to the object.
	 * @return the object if in the cache, or null(?).
	 */
	public Object getObject(CacheModel cacheModel, Object key) {
		Object result = null;
		Element element = getCache(cacheModel).get(key);
		if (element != null) {
			result = element.getObjectValue();
		}
		return result;

	}

	/**
	 * Put an object into a cache model.
	 *
	 * @param cacheModel
	 *            - the model to add the object to.
	 * @param key
	 *            - the key to the object.
	 * @param object
	 *            - the object to add.
	 */
	public void putObject(CacheModel cacheModel, Object key, Object object) {
		getCache(cacheModel).put(new Element(key, object));
	}

	/**
	 * Remove an object from a cache model.
	 *
	 * @param cacheModel
	 *            - the model to remove the object from.
	 * @param key
	 *            - the key to the object.
	 * @return the removed object(?).
	 */
	public Object removeObject(CacheModel cacheModel, Object key) {
		Object result = this.getObject(cacheModel, key);
		getCache(cacheModel).remove(key);
		return result;
	}

	/**
	 * Gets an EH Cache based on an iBatis cache Model.
	 *
	 * @param cacheModel
	 *            - the cache model.
	 * @return the EH Cache.
	 */
	private Cache getCache(CacheModel cacheModel) {
		String cacheName = cacheModel.getId();
		Cache cache = cacheManager.getCache(cacheName);
		return cache;
	}

	/**
	 * Shut down the EH Cache CacheManager.
	 */
	public void finalize() {
		if (cacheManager != null) {
			cacheManager.shutdown();
		}
	}

	/**
	 * Configure a cache controller. Initialize the EH Cache Manager as a
	 * singleton.
	 *
	 * @param props
	 *            - the properties object continaing configuration information.
	 */
	@Override
	public void configure(Properties props) {
		String configLocation = props.getProperty(CONFIG_LOCATION);
		// if can not found ehcache.xml from configLocaion,
		// use default configure file.
		if (configLocation == null) {
			configLocation = DEFAULT_CONFIG_LOCATION;
		}
		URL url = getClass().getResource(configLocation);
		cacheManager = CacheManager.create(url);
	}
}

这里默认在根目录下获取ehcache.xml文件，可以通过cacheModel配置进行修改。

在SqlMapConfig.xml文件中配置一个别名，作为全局变量，供其余SqlMap使用

<typeAlias
		alias="EHCACHE"
		type="com.ibatis.sqlmap.engine.cache.ehcache.EhCacheController" />

顺便提一句，要使用缓存注意SqlMapConfig.xml文件中settings节点配置cacheModelsEnabled为true！

	<settings
		cacheModelsEnabled="true"
		useStatementNamespaces="true"
		...
	/>

如果要变更ehcache.xml文件路径为/config/ehcache.xml，可以在上述节点中下入如下代码：

<property name="configLocation" value="/config/ehcache.xml" />

然后，就可以通过ehcache.xml控制ehcache缓存了！

举例说明iBatis SqlMap & ehcahce.xml，以免有些兄弟混淆！

以Account类为示例，在SqlMap中的配置为：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE sqlMap
    PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
    "http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap
	namespace="Account">
	<cacheModel
		id="cache"
		type="EHCACHE">
		<flushInterval
			hours="1" />
		<!-- flush操作,需要指明 Namespace -->
		<flushOnExecute
			statement="Account.create" />
	</cacheModel>
	<typeAlias
		alias="account"
		type="org.zlex.acl.Account" />
	<resultMap
		id="accountMap"
		class="account">
		<result
			property="accountId"
			column="accountId" />
		<result
			property="accountName"
			column="accountName" />
		<result
			property="mail"
			column="mail" />
		<result
			property="realName"
			column="realName" />
		<result
			property="status"
			column="status" />
		<result
			property="lastLoginTime"
			column="lastLoginTime" />
	</resultMap>
	<select
		id="readByAccountName"
		parameterClass="string"
		resultMap="accountMap"
		cacheModel="cache">
		<![CDATA[
			SELECT
				accountId,
				accountName,
				mail,
				realName,
				status,
				lastLoginTime
			FROM
				acl_account
			WHERE
				accountName = #accountName#
		]]>
	</select>
	<insert
		id="create"
		parameterClass="account">
		<![CDATA[
			INSERT INTO
				acl_account(
				accountName,
				mail,
				realName,
				status,
				lastLoginTime
				)
			VALUES (
					#accountName#,
					#mail#,
					#realName#,
					#status#,
					#lastLoginTime#
				)
		]]>
		<selectKey
			resultClass="long"
			keyProperty="accountId">
			<![CDATA[select LAST_INSERT_ID() as id ]]>
		</selectKey>
	</insert>
</sqlMap>

注意：

引用

<select
id="readByAccountName"
parameterClass="string"
resultMap="accountMap"
cacheModel="cache">

这里的cacheModel="cache"，对应的在ehcache.xml中就应该是：

	<cache
		name="Account.cache"
		maxElementsInMemory="10000"
		eternal="false"
		maxElementsOnDisk="1000"
		overflowToDisk="true"
		timeToIdleSeconds="300"
		/>

因为，我使用了useStatementNamespaces="true"