Mybatis源码之Statement处理器SimpleStatementHandler（四）

SimpleStatementHandler就是使用基本的Statement来执行query、batch、update等操作，其实现还是比较简单的，当然在执行过程中会涉及keyGenerator和ResultHandler操作，这些我们会在接下来的博客中进行详解。SimpleStatementHandler用于执行简单的sql语句，这里简单的sql语句是指sql语句中没有变量，不会通过外部进行参数传入的sql语句。

源码如下：

/**
 * @author Clinton Begin
 */
public class SimpleStatementHandler extends BaseStatementHandler {

  public SimpleStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
  }

  @Override
  public int update(Statement statement) throws SQLException {
	//获得sql语句
    String sql = boundSql.getSql();
	//获得参数
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    int rows;
	//statement执行sql语句返回更新数目
    if (keyGenerator instanceof Jdbc3KeyGenerator) {
      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 {
	  //如果没有keyGenerator，直接调用Statement.execute和Statement.getUpdateCount
      statement.execute(sql);
      rows = statement.getUpdateCount();
    }
    return rows;
  }

  @Override
  public void batch(Statement statement) throws SQLException {
	//批处理
    String sql = boundSql.getSql();
    statement.addBatch(sql);
  }

  //ResultHandler resultHandler这个参数好像没用啊
  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    String sql = boundSql.getSql();
	//statement执行sql语句
    statement.execute(sql);
    return resultSetHandler.<E>handleResultSets(statement);
  }

  //实例化Statement
  @Override
  protected Statement instantiateStatement(Connection connection) throws SQLException {
    if (mappedStatement.getResultSetType() != null) {
      return connection.createStatement(mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.createStatement();
    }
  }

  @Override
  public void parameterize(Statement statement) throws SQLException {
    // N/A
  }

}