Where to close a JDBC Connection while I want to r

Question

It seems that the ResultSet will be automatically closed when I close the Connection. But I want to return the ResultSet and use it in another method, then I don't know where to close Connection and PreparedStatement.

public ResultSet executeQuery(String sql, String[] getValue)
{
    Connection conn = null;
    PreparedStatement pstmt = null;
    ResultSet rs = null;
    try
    {
        conn = getConn();
        pstmt = conn.prepareStatement(sql);
        if (getValue != null)
        {
            for (int i = 0; i < getValue.length; i++)
            {
                pstmt.setString(i + 1, getValue[i]);
            }
        }
        rs = pstmt.executeQuery();
    } catch (Exception e)
    {
        e.printStackTrace();
        closeAll(conn, pstmt, rs);
    }
    return rs;
}

I've moved closeAll(conn, pstmt, null); into catch block because I found that if I put it in finally block I'll lost my rs immediately just before it returns. Now when I want to close the rs, I can't close the conn and pstmt. Is there any solution?

Answer 1

You really shouldn't handle with JDBC at the lower level. Use a framework like spring instead, it will handle all required close() operations for you.

Answer 2

You can't use ResultSet after you've closed Connection and/or PreparedStatement. So, you need to pass an object on which to make a callback into this method.

All cleanup should be done in finally blocks.

Rewrite it like this

public ResultSet executeQuery(
    String sql,
    String[] getValue,
    CallbackObj cbObj
  ) throws SQLException
{
  final Connection conn = getConn( );

  try
  {
    final PreparedStatement pstmt = conn.prepareStatement(sql);

    try
    {
      if (getValue != null)
      {
        for (int i = 0; i < getValue.length; i++)
        {
          pstmt.setString(i + 1, getValue[i]);
        }
      }

      final ResultSet rs = pstmt.executeQuery();

      try
      {
        cbObj.processResultSet( rs );
      }
      finally
      {
        // You may want to handle SQLException
        // declared by close
        rs.close( );
      }
    }
    finally
    {
      // You may want to handle SQLException
      // declared by close
      pstmt.close( );
    }
  }
  finally
  {
    // You may want to handle SQLException
    // declared by close
    conn.close( );
  }
}

Answer 3

The cleaner way is to use CachedRowSetImpl. But on MySQL 5.x+ there are some bugs with selecting columns by name or label.

For use with MySQL use this version: https://stackoverflow.com/a/17399059/1978096

Answer 4

I'd recommend that you do something more like this:

public List<Map> executeQuery(Connection connection, String sql) throws SQLException
{
    List<Map> rows = new ArrayList<Map>();

    PreparedStatement stmt = null;
    ResultSet rs = null;

    try
    {
        pstmt = conn.prepareStatement(sql);
        rs = stmt.execute();
        int numColumns = rs.getMetaData().getColumnCount();

        while (rs.next())
        {
            Map<String, Object> row = new LinkedHashMap<String, Object>();
            for (int i = 0; i < numColumns; ++i)
            {
                String column = rs.getColumnName(i+1);
                Object value = rs.getObject(i+1);
                row.put(column, value);
            }
            rows.add(row);
        }
    } 
    finally
    {
        close(rs);
        close(stmt);
    }

    return rows;
}

public static void close(Statement s)
{
    try
    {
        if (s != null)
        {
            s.close();
        }
    }
    catch (SQLException e)
    {
        e.printStackTrace();
    }
}

public static void close(ResultSet rs)
{
    try
    {
        if (rs != null)
        {
            rs.close();
        }
    }
    catch (SQLException e)
    {
        e.printStackTrace();
    }
}