Mybatis学习笔记(十七)【mybatis整合ehcache】

Contents

• 分布缓存
• 整合方法(掌握)
  
  • 整合ehcache
  • 加入ehcache的配置文件

---

ehcache是一个分布式缓存框架

分布缓存

我们系统为了提高系统并发，性能、一般对系统进行分布式部署（集群部署方式）

不使用分布缓存，缓存的数据在各各服务单独存储，不方便系统开发。所以要使用分布式缓存对缓存数据进行集中管理。

mybatis无法实现分布式缓存，需要和其它分布式缓存框架进行整合。

整合方法(掌握)

mybatis提供了一个cache接口，如果要实现自己的缓存逻辑，实现cache接口开发即可。

mybatis和ehcache整合，mybatis和ehcache整合包中提供了一个cache接口的实现类。

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);

  /**
   * Optional. It is not called by the core.
   * 
   * @param key The key
   * @return The object that was removed
   */
  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();

}

mybatis默认实现cache类是：

package org.apache.ibatis.cache.impl;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;

import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.cache.CacheException;

/**
 * @author Clinton Begin
 */
public class PerpetualCache implements Cache {

  private String id;

  private Map<Object, Object> cache = new HashMap<Object, Object>();

  public PerpetualCache(String id) {
    this.id = id;
  }

  public String getId() {
    return id;
  }

  public int getSize() {
    return cache.size();
  }

  public void putObject(Object key, Object value) {
    cache.put(key, value);
  }

  public Object getObject(Object key) {
    return cache.get(key);
  }

  public Object removeObject(Object key) {
    return cache.remove(key);
  }

  public void clear() {
    cache.clear();
  }

  public ReadWriteLock getReadWriteLock() {
    return null;
  }

  public boolean equals(Object o) {
    if (getId() == null) throw new CacheException("Cache instances require an ID.");
    if (this == o) return true;
    if (!(o instanceof Cache)) return false;

    Cache otherCache = (Cache) o;
    return getId().equals(otherCache.getId());
  }

  public int hashCode() {
    if (getId() == null) throw new CacheException("Cache instances require an ID.");
    return getId().hashCode();
  }

}

整合ehcache

• 加入ehcache包
  
  • ehcache-core-2.6.5.jar
  • mybatis-ehcache-1.0.2.jar

配置mapper中cache中的type为ehcache对cache接口的实现类型

 <!-- 开启本mapper的namespace下的二级缓存
    type：指定cache接口的实现类的类型，mybatis默认使用PerpetualCache
    要和ehcache整合，需要配置type为ehcache实现cache接口的类型
    <cache />
    -->
    <cache type="org.mybatis.caches.ehcache.EhcacheCache"/>

加入ehcache的配置文件

在classpath下配置ehcache.xml

<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
    <diskStore path="F:\develop\ehcache" />
    <defaultCache 
        maxElementsInMemory="1000" 
        maxElementsOnDisk="10000000"
        eternal="false" 
        overflowToDisk="false" 
        timeToIdleSeconds="120"
        timeToLiveSeconds="120" 
        diskExpiryThreadIntervalSeconds="120"
        memoryStoreEvictionPolicy="LRU">
    </defaultCache>
</ehcache>