（异常）java.sql.SQLException: 未调用 ResultSet.next

╰半橙微兮° 2022-05-14 03:34 197阅读 0赞

### 当用**ResultSet**接收来自数据库查询的结果集时，即使结果集只有一条数据，也需要用到**resultSet.next()**函数移动游标获取数据。 ###

不然会报未调用 ResultSet.next异常

错误写法

try {
        pstm=connection.prepareStatement("select * from account where card_id=?");
        pstm.setInt(1, card_id);
    			
        resultSet = pstm.executeQuery();
            account.setCard_id(resultSet.getInt(1));
            account.setUsername(resultSet.getString(2));
            account.setPassword(resultSet.getString(3));
            account.setBalance(resultSet.getDouble(4));
            account.setMobile(resultSet.getString(5));
    
    }

正确写法

pstm=connection.prepareStatement("select * from account where card_id=?");
        pstm.setInt(1, card_id);
        resultSet = pstm.executeQuery();
        while (resultSet.next()) {
            account.setCard_id(resultSet.getInt(1));
            account.setUsername(resultSet.getString(2));
            account.setPassword(resultSet.getString(3));
            account.setBalance(resultSet.getDouble(4));
            account.setMobile(resultSet.getString(5));
        }

ResultSet.next 注释信息

public interface ResultSet extends Wrapper, AutoCloseable {
    
        /**
         * Moves the cursor forward one row from its current position.
         * A <code>ResultSet</code> cursor is initially positioned
         * before the first row; the first call to the method
         * <code>next</code> makes the first row the current row; the
         * second call makes the second row the current row, and so on.
         * <p>
         * When a call to the <code>next</code> method returns <code>false</code>,
         * the cursor is positioned after the last row. Any
         * invocation of a <code>ResultSet</code> method which requires a
         * current row will result in a <code>SQLException</code> being thrown.
         *  If the result set type is <code>TYPE_FORWARD_ONLY</code>, it is vendor specified
         * whether their JDBC driver implementation will return <code>false</code> or
         *  throw an <code>SQLException</code> on a
         * subsequent call to <code>next</code>.
         *
         * <P>If an input stream is open for the current row, a call
         * to the method <code>next</code> will
         * implicitly close it. A <code>ResultSet</code> object's
         * warning chain is cleared when a new row is read.
         *
         * @return <code>true</code> if the new current row is valid;
         * <code>false</code> if there are no more rows
         * @exception SQLException if a database access error occurs or this method is
         *            called on a closed result set
         */
        boolean next() throws SQLException;

从此接口的方法注释中**第二行和第三行**可以看见

A <code>ResultSet</code> cursor is initially positioned  
     \* before the first row;

游标的初始位置为第一行的前面。

因此不调用next方法就从resultSet中获取数据是不可取的。