这是一种简单的行计数方法。

ResultSet rs = job.getSearchedResult(stmt);
int rsCount = 0;

//but notice that you'll only get correct ResultSet size after end of the while loop
while(rs.next())
{
    //do your other per row stuff 
    rsCount = rsCount + 1;
}//end while

这是一种简单的行计数方法。

ResultSet rs = job.getSearchedResult(stmt);
int rsCount = 0;

//but notice that you'll only get correct ResultSet size after end of the while loop
while(rs.next())
{
    //do your other per row stuff 
    rsCount = rsCount + 1;
}//end while

今天，我用了这个逻辑，为什么我不知道得到RS的计数。

int chkSize = 0;
if (rs.next()) {
    do {  ..... blah blah
        enter code here for each rs.
        chkSize++;
    } while (rs.next());
} else {
    enter code here for rs size = 0 
}
// good luck to u.

SELECT COUNT(*) FROM…查询。

OR

int size =0;
if (rs != null) 
{
  rs.last();    // moves cursor to the last row
  size = rs.getRow(); // get row id 
}

在这两种情况下，都不需要遍历整个数据。

为列命名。

String query = "SELECT COUNT(*) as count FROM

引用该列从ResultSet对象到int，并从那里做你的逻辑。

PreparedStatement statement = connection.prepareStatement(query);
statement.setString(1, item.getProductId());
ResultSet resultSet = statement.executeQuery();
while (resultSet.next()) {
    int count = resultSet.getInt("count");
    if (count >= 1) {
        System.out.println("Product ID already exists.");
    } else {
        System.out.println("New Product ID.");
    }
}

(速度考虑)

很多人在这里建议ResultSet.last()，但你需要打开连接作为一个ResultSet。TYPE_SCROLL_INSENSITIVE，对于Derby嵌入式数据库，它比ResultSet.TYPE_FORWARD_ONLY慢10倍。

根据我对嵌入式Derby和H2数据库的微型测试，在SELECT之前调用SELECT COUNT(*)要快得多。

下面是我的代码和基准测试的更详细信息