时间:2021-07-01 10:21:17 帮助过:37人阅读
判断查询结果是否为空 在JDBC中没有方法hasNext去判断是否有下一条数据,但是我们可以使用next方法来代替。看next方法的官方解释: booleannext() throws Moves the cursor forward one row from its current position. A ResultSet cursor is initially pos
boolean next() throwsMoves the cursor forward one row from its current position. A
ResultSet
cursor is initially positioned before
the first row; the first call to the method next
makes the first row the current row; the second call makes the second row the current row, and so
on.
When a call to the next
method returns false
,
the cursor is positioned after the last row. Any invocation of a ResultSet
method which requires a current row will result in a SQLException
being
thrown. If the result set type is TYPE_FORWARD_ONLY
, it is vendor specified whether their JDBC driver implementation will return false
or
throw an SQLException
on a subsequent call to next
.
If an input stream is open for the current row, a call to the method next
will
implicitly close it. A ResultSet
object's warning chain is cleared when a new row is read.
true
if the new current row is valid; false
if
there are no more rowsSQLException
-
if a database access error occurs or this method is called on a closed result setResultSet
的请求当前行的方法调用都会导致SQLException
被抛出。但如果查询的结果设置为TYPE_FORWARD_ONLY,next方法在这时候根据实现厂商的不同,可能会返回false也坑能会抛出SQLException
异常
的警告将会被清楚。
Statement statement = conn.createStatement(); ResultSet res = statement.executeQuery(selectSql); if (!res.next()) { //res is null } else { // res is not null }
ResultSet res = ...使用某种方法获取查询结果 int nRow = 0; while(res.next()) { ++nRow; } res.beforeFirst(); // 其他代码不变
ResultSet res = ...使用某种方法获取查询结果 res.last(); final int nRow = res.getRow(); res.beforeFirst(); // 其他代码不变