如何运行Resultset.next()两次？

Question

我有这个方法来获取一串行并打印它们.

另外,我要做while(Resultset.next())两次.第一个是获取行数,第二个是打印字符串.但是当方法第一次运行时Resultset.next(),方法会跳过第二次Resultset.next().

public static String[] gett() throws ClassNotFoundException, SQLException{

    // this for get conneced to the database .......................

    Class.forName("oracle.jdbc.driver.OracleDriver");
    Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE","hr","111"); 
    Statement st = conn.createStatement();
    ResultSet re = st.executeQuery("select location_id from DEPARTMENTS");

    // Ok , now i have the ResultSet ...

    // the num_row it's counter to get number of rows
    int num_row = 0;

    // this Arrar to store String values
    String[] n = new String[num_row];

    // this is the first ResultSet.next , and it's work ..!
    // also , this ResultSet.next work to get number on rows and store the number on 'num_row' 
    while(re.next())
        num_row++;

    // NOW , this is the secound 'ResultSet.next()' , and it's doesn't WORK !!!!
    while(re.next()) {
        System.out.println(re.getString("location_id"));
    }
}

问题是,第一个Resultset.next()工作正常,但第二个不起作用!

有人能解释为什么吗？我怎样才能让它发挥作用？

注意:我知道,还有另外一种方法可以做到这一点,Resultset.next() 但我想做两次;)

Answer 1

你可以初始化你Statement的如下

conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);

因此,您可以在Statement中移动光标.

现在你可以循环它.

while(re.next())
    num_row++;
re.beforeFirst();

但这是非常必要的,最佳解决方案是跳转到集合的末尾并返回行

num_row = 0;
if(re.last()) {
   num_row = rs.getRow();
   re.beforeFirst();
}