聊聊jdbc statement的fetchSize

    @Test
    public void testReadTimeout() throws SQLException {
        Connection connection = dataSource.getConnection();
        //https://jdbc.postgresql.org/documentation/head/query.html
        connection.setAutoCommit(false); //NOTE 为了设置fetchSize,必须设置为false

        String sql = "select * from demo_table";
        PreparedStatement pstmt;
        try {
            pstmt = (PreparedStatement)connection.prepareStatement(sql);
            pstmt.setFetchSize(50); 
            System.out.println("ps.getQueryTimeout():" + pstmt.getQueryTimeout());
            System.out.println("ps.getFetchSize():" + pstmt.getFetchSize());
            System.out.println("ps.getFetchDirection():" + pstmt.getFetchDirection());
            System.out.println("ps.getMaxFieldSize():" + pstmt.getMaxFieldSize());

            ResultSet rs = pstmt.executeQuery(); 
            //NOTE 这里返回了就代表statement执行完成,默认返回fetchSize的数据
            int col = rs.getMetaData().getColumnCount();
            System.out.println("============================");
            while (rs.next()) { 
                for (int i = 1; i <= col; i++) {
                    System.out.print(rs.getObject(i));
                }
                System.out.println("");
            }
            System.out.println("============================");
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //close resources
        }
    }