错误原因：

如API中所述

API：

A table of data representing a database result set, which is usually generated by executing a statement that queries the database. AResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. Thenext method moves the cursor to the next row。

就是说游标初始化的位置在首行之前。

解决方法：

在使用rs前要调用rs.next()方法