ibatis缓存的简单使用和源码分析

配置：

    <cacheModel type="LRU" id="user-cache">

        <flushInterval hours="24"/>

        <flushOnExecute statement="user.addUser"/>

        <flushOnExecute statement="user.updateUser"/>

        <flushOnExecute statement="user.deleteUser"/>

        <property name="cache-size" value="50000"/>

    </cacheModel>

 

    <select id="getAll" resultClass="user" parameterClass="java.util.HashMap" cacheModel="user-cache">

        select * from user limit 0,#size#

    </select>

 

测试代码：

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("size", 8);

        // first time no cache

        Long startTime = System.currentTimeMillis();

        List<User> list = (List<User>)sqlMap.queryForList("user.getAll", map);

        System.out.println("No cache pass time:" + (System.currentTimeMillis() - startTime));

        // second time has cache

        map.put("size", 8);

        startTime = System.currentTimeMillis();

        list = (List<User>)sqlMap.queryForList("user.getAll", map);

        System.out.println("Has cache pass time:" + (System.currentTimeMillis() - startTime));

 

结果：

No cache pass time:485

Has cache pass time:0

打开ibatis的日志，会发现第二次执行没有sql语句输出。

 

注意：

CacheModel缓存的是statement，即key是跟sql语句相关，如果sql语句不一样，将产生两个cache，如第二条将使用不到缓存,但第三条可以使用缓存：

select * from user limit 0,4    新建缓存

select * from user limit 0,8    新建缓存

select * from user limit 0,8    使用缓存

 

简单源码分析：

以queryForList为例：

 

SqlMapExecutorDelegate具体实现：

list = ms.executeQueryForList(statementScope, trans, paramObject, skip, max);

这里ms为MappedStatement，其中CachingStatement是它的子类。

 

CachingStatement具体实现：

  public List executeQueryForList(StatementScope statementScope, Transaction trans, Object parameterObject, int skipResults, int maxResults)

      throws SQLException {

    CacheKey cacheKey = getCacheKey(statementScope, parameterObject);

    cacheKey.update("executeQueryForList");

    cacheKey.update(skipResults);

    cacheKey.update(maxResults);

    Object listAsObject = cacheModel.getObject(cacheKey);

    List list;

    if(listAsObject == CacheModel.NULL_OBJECT){

      // The cached object was null

      list = null;

    }else if (listAsObject == null) {

      list = statement.executeQueryForList(statementScope, trans, parameterObject, skipResults, maxResults);

      cacheModel.putObject(cacheKey, list);

    }else{

      list = (List) listAsObject;

    }

    return list;

  }