Mybatis的cache

相关类：org.apache.ibatis.executor.CachingExecutor

相关代码：

  public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
    BoundSql boundSql = ms.getBoundSql(parameterObject);
    CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
    return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
  }

从CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);可以看出，当下列四个元素相同时会使用cache：

MappedStatement（一般为xml中定义）、parameterObject（传递给xml的参数）、rowBounds（分页参数）、boundSql（最终sql，由MappedStatement和parameterObject决定）

createCacheKey的代码：

  public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {
    if (closed) throw new ExecutorException("Executor was closed.");
    CacheKey cacheKey = new CacheKey();
    cacheKey.update(ms.getId());
    cacheKey.update(rowBounds.getOffset());
    cacheKey.update(rowBounds.getLimit());
    cacheKey.update(boundSql.getSql());
    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    if (parameterMappings.size() > 0 && parameterObject != null) {
      TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();
      if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
        cacheKey.update(parameterObject);
      } else {
        MetaObject metaObject = configuration.newMetaObject(parameterObject);
        for (ParameterMapping parameterMapping : parameterMappings) {
          String propertyName = parameterMapping.getProperty();
          if (metaObject.hasGetter(propertyName)) {
            cacheKey.update(metaObject.getValue(propertyName));
          } else if (boundSql.hasAdditionalParameter(propertyName)) {
            cacheKey.update(boundSql.getAdditionalParameter(propertyName));
          }
        }
      }
    }
    return cacheKey;
  }