如何从选择查询的结果集创建Java对象？

连接到JDBC工作正常。 这是访问数据库表的代码。 文件名 –

FlightDB.java架构 – Flights1（flno int，时间戳）

public static Flight selectFlight(Flight flight) throws SQLException{ PreparedStatement ps = null; ResultSet rs = null; String q1 = "Select * from Flights1 f order by f.time"; Flight flight1 = null; try{ ps = connection.prepareStatement(q1); rs = ps.executeQuery(); while(rs.next()){ Flight flight1 = new Flight(); flight1 = new Flight(); flight1.setflno(rs.getInt(1)); flight1.settime(rs.getTimestamp(2)); // System.out.println(“new flight:” +flight1.getflno()); Correct output printed here } } finally{ closeResultSet(rs); closePreparedStatement(ps); } return flight; } 

这是顶级代码的一部分————文件名：Display.java

 static Flight showFlights(ResultSet rs) throws SQLException { Flight flight1 = new Flight(); AirDB.selectFlight(flight1); // flight1.setflno(rs.getInt(1)); // flight1.settime(rs.getTimestamp(2)); System.out.println("New flight " + flight1.getflno());//OP: New flight 0 return flight1; } 

这是我的class级Flight —- Flight.java

 public Flight() { flno = 0; time = null; } public Flight(int flno ,Timestamp time) { this.flno = flno; this.time = time; } public int getflno(){ return flno; } public void setflno(int flno){ this.flno = flno; } public Timestamp gettime(){ return time; } public void settime(Timestamp time){ this.time = time; } 

我得到0（默认值）作为我的输出不正确。 我想打印顶级java文件的输出。 我尝试使用flight1 = AssignFlights1.showFlights（rs）; 在FlightDB.java中也是如此。

感谢您查看此代码。 你能帮帮我吗？ 谢谢。

Answer 1

您将返回错误的对象（另请参阅我的内联注释）

尝试

 public static Flight selectFlight() throws SQLException{ // no param needed PreparedStatement ps = null; ResultSet rs = null; // I guess that this will not be the query you want in the end String q1 = "Select * from Flights1 f order by f.time"; Flight flight1 = null; try{ ps = connection.prepareStatement(q1); rs = ps.executeQuery(); if (rs.next()){ // only returning one object so no needed for while flight1 = new Flight(); flight1.setflno(rs.getInt(1)); flight1.settime(rs.getTimestamp(2)); System.out.println(“new flight:” +flight1.getflno()); Correct output printed here } } finally{ closeResultSet(rs); closePreparedStatement(ps); } return flight1; } 

此外，如果您正确缩进代码，则更容易阅读和调试

Answer 2

你应该返回flight1对象而不是flight ，如下所示：

 public static Flight selectFlight() throws SQLException{ PreparedStatement ps = null; ResultSet rs = null; String q1 = "Select * from Flights1 f order by f.time"; Flight flight1 = null; try{ ps = connection.prepareStatement(q1); rs = ps.executeQuery(); if(rs.next()){ flight1 = new Flight(); flight1.setflno(rs.getInt(1)); flight1.settime(rs.getTimestamp(2)); // System.out.println(“new flight:” +flight1.getflno()); Correct output printed here } } finally{ closeResultSet(rs); closePreparedStatement(ps); } return flight1; } 

另外，不要使用while作为单个记录，而是使用if单个记录。