Mybatis源码笔记（四）、StatementHandler

在上一节中我们看到，Statement 处理主要由 StatementHandler 接口实现,StatementHandler 由 configuration.newStatementHandler 创建

 StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.update(stmt);


public StatementHandler newStatementHandler(Executor executor,
MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }

//   根据 不同的类型创建不同的StatementHandler
    public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {

    switch (ms.getStatementType()) {
      case STATEMENT:
        delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case PREPARED:
        delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case CALLABLE:
        delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      default:
        throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
    }

  }

我们看一下 StatementHandler 接口的方法

public interface StatementHandler {

Statement prepare(Connection connection, Integer transactionTimeout)
throws SQLException;

void parameterize(Statement statement)
throws SQLException;

void batch(Statement statement)
throws SQLException;

int update(Statement statement)
throws SQLException;

<E> List<E> query(Statement statement, ResultHandler resultHandler)
throws SQLException;

<E> Cursor<E> queryCursor(Statement statement)
throws SQLException;

BoundSql getBoundSql();

ParameterHandler getParameterHandler();

}

我们选取其中的 SimpleStatementHandler 来具体分析下,SimpleStatementHandler 继承了 BaseStatementHandler，BaseStatementHandler 实现了 StatementHandler 接口

public abstract class BaseStatementHandler implements StatementHandler {

// 配置
  protected final Configuration configuration;
  protected final ObjectFactory objectFactory;
  protected final TypeHandlerRegistry typeHandlerRegistry;
//结果处理
  protected final ResultSetHandler resultSetHandler;
//参数处理
  protected final ParameterHandler parameterHandler;
// 具体的执行器
  protected final Executor executor;
//   mappedStatement
  protected final MappedStatement mappedStatement;
  ......
}

// 继承实现类SimpleStatementHandler
public class SimpleStatementHandler extends BaseStatementHandler {
    ......
      @Override
  public int update(Statement statement) throws SQLException {
    //   执行SQL
    String sql = boundSql.getSql();
    // SQL param
    Object parameterObject = boundSql.getParameterObject();
    // 主键生成方式
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    int rows;
    // 根据不同的keyGenerator，传入 不同的参数执行，最后返回结果
    if (keyGenerator instanceof Jdbc3KeyGenerator) {
        // 很熟悉的味道
      statement.execute(sql, Statement.RETURN_GENERATED_KEYS);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else if (keyGenerator instanceof SelectKeyGenerator) {
      statement.execute(sql);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else {
      statement.execute(sql);
      rows = statement.getUpdateCount();
    }
    // 返回结果
    return rows;
  }
    ......
}

上面的 update 方法我们终于找到了熟悉的东西，JDBC 的 statement 执行，至此，一切都清楚了。其实万变不离其宗，只是框架让我们可以脱离一些低级、重复劳动，优化性能，比我们自己徒手实现的要好。但是归根结底还是基础，所以基础还是要打牢的。