IBatis框架的一些问题的扩展（二）

            项目中由于Ibatis自身的缓存的鸡肋性（Ibatis自身的缓存是查询字符串和相应的结果的缓存，效率非常有效并且很容易占用内存，采用大量的缓存时，Ibatis严重的影响效率），进行相应的扩展的采用OSCache进行对象缓存。

 iBatis整理——EhCache支持扩展

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"
    ...
/>

接下来，在SqlMap.xml文件中的cacheModel中 

<cacheModel
    id="cache"
    type="EHCACHE">
...
</cacheModel>

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"

package easyway.tbs.framework.cache;

import java.io.Serializable;

import java.util.Set;

/**

 * cache 通用接口

 *

 * @author longgangbai

 */

publicinterface Cache extends Serializable {

    public Object get(Object key);

    publicvoid put(Object key, Object value);

    publicvoid remove(Object key);

    publicvoid clear();

    publicint size();

    @SuppressWarnings("unchecked")

    public Set keys();

    @SuppressWarnings("unchecked")

    public Set values();

}

package easyway.tbs.framework.cache;

import easyway.tbs.framework.app.exceptions.SystemException;

/**

 * CacheManager提供和维护Cache生命周期实例

 *

 * @authorlonggangbai

 */

 

publicinterface CacheManager {

    /**

     * 根据指定的名称获取Cache实现，

     * 如果指定的名称的cache还不存，

     * 则以名称建立一个cache

     * 并返回cache对象

     *  

     * @param name 要获得的cache名称.

     * @return Cache 返回指定名称的cache实例   

     */

    public Cache getCache(String name)  throws SystemException;

    publicvoid destroy(String name) throws SystemException;

    }

package easyway.tbs.framework.cache;

import java.util.HashMap;

import java.util.Map;

import easyway.tbs.framework.app.exceptions.SystemException;

/**

 * 默认的内存缓存管理器

 *

 * @authorlonggangbai

 */

 

publicclass DefaultCacheManager implements CacheManager  {

 

    /**

     * DefaultCacheManager维护内存缓存对象

     */

    privatestaticfinal Map<String, Cache> caches = new HashMap<String, Cache>();

    /*

     * 获得指定的名称cache对象

     *

     * @see

     * easyway.tbs.framework.app.cache.CacheManager#getCache(java.lang.String)

     */

    public Cache getCache(String name) {

        if (name == null) {

            thrownew SystemException("cache-001", "缓存名称不能为空");

        }

        Cache cache;

        synchronized (caches) {

            cache = caches.get(name);

            if (cache == null) {

                cache = new SoftHashMapCache(name);

                caches.put(name, cache);

            }

        }

        return cache;

    }

 

    publicvoid destroy(String name) throws SystemException {

       

        synchronized (caches) {    

                caches.remove(name);

            }

        }

    }

     项目建议：实现Ibatis的缓存的扩展建议采用mechcache或者xmechcache的分布式缓存功能，mechcache为分布式的缓存，性能各方面的比较优越。使用OSCache可以参考Spring或者Jforum中Cache的设计思路。