Mybatis源碼之Statement處理器PreparedStatementHandler（五）

PreparedStatementHandler就是調用PreparedStatement來執行SQL語句，這樣在第一次執行sql語句時會進行預編譯，在接下來執行相同的SQL語句時會提高資料庫性能

/**
 * @author Clinton Begin
 */
/* 使用PrepareStatement**/
public class PreparedStatementHandler extends BaseStatementHandler {

  public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
  }
  //
  public int update(Statement statement) throws SQLException {
  //使用PrepareStatement
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    int rows = ps.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
  //keyGenerator在執行之後運作
    keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
    return rows;
  }
  //使用PrepareStatement的批處理
  public void batch(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.addBatch();
  }
  //使用PrepareStatement的execute操作
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
  //操作結果在ResultHandler中處理
    return resultSetHandler.<E> handleResultSets(ps);
  }
  //獲得Statement
  protected Statement instantiateStatement(Connection connection) throws SQLException {
    String sql = boundSql.getSql();
  //根據KeyGenerator設定值的傳回key的名稱
    if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
      String[] keyColumnNames = mappedStatement.getKeyColumns();
      if (keyColumnNames == null) {
        return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
      } else {
        return connection.prepareStatement(sql, keyColumnNames);
      }
    } else if (mappedStatement.getResultSetType() != null) {
      return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.prepareStatement(sql);
    }
  }

  public void parameterize(Statement statement) throws SQLException {
    parameterHandler.setParameters((PreparedStatement) statement);
  }

}