executor包执行器功能

public interface Executor {
 
  ResultHandler NO_RESULT_HANDLER = null;
 
  // 数据更新操作，其中数据的增加、删除、更新均可由该方法实现
  int update(MappedStatement ms, Object parameter) throws SQLException;
  // 数据查询操作，返回结果为列表形式
  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey cacheKey, BoundSql boundSql) throws SQLException;
  // 数据查询操作，返回结果为列表形式
  
  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;
  // 数据查询操作，返回结果为游标形式
  <E> Cursor<E> queryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds) throws SQLException;
  // 清理缓存
  List<BatchResult> flushStatements() throws SQLException;
  // 提交事务
  void commit(boolean required) throws SQLException;
  // 回滚事务
  void rollback(boolean required) throws SQLException;
  // 创建当前查询的缓存键值
  CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql);
  // 本地缓存是否有指定值
  boolean isCached(MappedStatement ms, CacheKey key);
  // 清理本地缓存
  void clearLocalCache();
  // 懒加载
  void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType);
  // 获取事务
  Transaction getTransaction();
  // 关闭执行器
  void close(boolean forceRollback);
  // 判断执行器是否关闭
  boolean isClosed();
  // 设置执行器包装
  void setExecutorWrapper(Executor executor);
 
}

public abstract class BaseExecutor implements Executor {
 
  private static final Log log = LogFactory.getLog(BaseExecutor.class);
 
  protected Transaction transaction;
  protected Executor wrapper;
 
  protected ConcurrentLinkedQueue<DeferredLoad> deferredLoads;
  // 查询操作的结果缓存
  protected PerpetualCache localCache;
  // Callable查询的输出参数缓存
  protected PerpetualCache localOutputParameterCache;
  protected Configuration configuration;
 
  protected int queryStack;
  private boolean closed;
 
 
 
 
  
  @Override
  public int update(MappedStatement ms, Object parameter) throws SQLException {
    ErrorContext.instance().resource(ms.getResource())
            .activity("executing an update").object(ms.getId());
    if (closed) {
      // 执行器已经关闭
      throw new ExecutorException("Executor was closed.");
    }
    // 清理本地缓存
    clearLocalCache();
    // 返回调用子类进行操作
    return doUpdate(ms, parameter);
  }
 
  
 
  
  @Override
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
    BoundSql boundSql = ms.getBoundSql(parameter);
    // 生成缓存的键
    CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
    return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
  }
 
  
  @SuppressWarnings("unchecked")
  @Override
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
    ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
    if (closed) {
      // 执行器已经关闭
      throw new ExecutorException("Executor was closed.");
    }
    if (queryStack == 0 && ms.isFlushCacheRequired()) { // 新的查询栈且要求清除缓存
      // 清除一级缓存
      clearLocalCache();
    }
    List<E> list;
    try {
      queryStack++;
      // 尝试从本地缓存获取结果
      list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
      if (list != null) {
        // 本地缓存中有结果，则对于CALLABLE语句还需要绑定到IN/INOUT参数上
        handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
      } else {
        // 本地缓存没有结果，故需要查询数据库
        list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
      }
    } finally {
      queryStack--;
    }
    if (queryStack == 0) {
      // 懒加载操作的处理
      for (DeferredLoad deferredLoad : deferredLoads) {
        deferredLoad.load();
      }
      deferredLoads.clear();
      // 如果本地缓存的作用域为STATEMENT，则立刻清除本地缓存
      if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
        clearLocalCache();
      }
    }
    return list;
  }
 
  
 
  
  @Override
  public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    // 创建CacheKey，并将所有查询参数依次更新写入
    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();
    TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();
    for (ParameterMapping parameterMapping : parameterMappings) {
      if (parameterMapping.getMode() != ParameterMode.OUT) {
        Object value;
        String propertyName = parameterMapping.getProperty();
        if (boundSql.hasAdditionalParameter(propertyName)) {
          value = boundSql.getAdditionalParameter(propertyName);
        } else if (parameterObject == null) {
          value = null;
        } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
          value = parameterObject;
        } else {
          MetaObject metaObject = configuration.newMetaObject(parameterObject);
          value = metaObject.getValue(propertyName);
        }
        cacheKey.update(value);
      }
    }
    if (configuration.getEnvironment() != null) {
      cacheKey.update(configuration.getEnvironment().getId());
    }
    return cacheKey;
  }
}