Question

我正在尝试使下面的示例代码正常工作，并且我在其中贴了一个println，上面只写着“ before”，当下面的代码运行时，控制台在“ before”之前打印，然后控制台在“”处打印“ exception”。 NextMonthNumbers.SQLConnector（NextMonthNumbers.java:35）“也是很多次。

我只希望下面的代码正常工作。我有很多要处理的String查询，我尝试使用1个连接来完成，所以它并不慢。

public class NextMonthNumbers {



public static Connection SQLConnector() throws SQLException {

    Connection con = null;
    PreparedStatement ps1,ps2= null;
    ResultSet rs,rs2=null;

        String query01="SELECT MAX(number)+1 FROM `Loads` WHERE month = 'Jan' AND `date_arrived` BETWEEN '2018-01-01' AND '2018-12-31'";
        String query02="SELECT MAX(number)+1 FROM `Loads` WHERE month = 'Feb' AND `date_arrived` BETWEEN '2018-01-01' AND '2018-12-31'";

 //testing for loop    System.out.println("before");
        ps1 =  SQLConnector().prepareStatement(query01);
        ps1.closeOnCompletion();
        ps2 =  SQLConnector().prepareStatement(query02);
        rs = ps1.executeQuery();
        rs2 = ps2.executeQuery();

    try{
        Class.forName("com.mysql.jdbc.Driver");
        String username = "Example";
        String password = "Example";
        String Database = "Example";
        con = DriverManager.getConnection(Database, username, password);
        con.setAutoCommit(false);
        System.out.println("*** Connecting to the database for Next Number ***");
        MiddleTextbottom.setText("Connecting to the database for Table Variables");


        while(rs.next()){
           query01 = rs.getString(1);

            if (rs.getString(ICONIFIED) ==null) {
                Main.UpdatedNextjan18.setText(query01);
                Main.UpdatedNextjan18.setText("1");
            }else{
                Main.UpdatedNextjan18.setText(query01);
            } 


        while(rs2.next()){
           query02 = rs2.getString(1);
            if (rs2.getString(ICONIFIED) ==null) {
                Main.UpdatedNextfeb18.setText(query02);
                Main.UpdatedNextfeb18.setText("1");
            }else{
                Main.UpdatedNextfeb18.setText(query02);
            } 

        }
        }


    } catch (ClassNotFoundException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println("Error: "+ex);
    } catch (SQLException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println(ex);
    }catch ( java.util.NoSuchElementException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println("Error: "+ex);

    }
    con.close();
    SQLConnector().close();
    return null;

        }

}

Answer 1

正如汤姆（Tom）所说，我的主要问题太明显了，我在内部调用了SQLException。因此，我做了一次小小的重写，并在try {}下面移动了一些代码以使其正常工作。

public static Connection SQLConnector() throws SQLException {

    Connection con = null;
    PreparedStatement ps,ps2 = null;
    ResultSet rs,rs2 = null;


    try{
        Class.forName("com.mysql.jdbc.Driver");
        String username = "Example";
        String password = "Example";
        String Database = "Example";
        con = DriverManager.getConnection(Database, username, password);
        con.setAutoCommit(false);
        System.out.println("*** Connecting to the database for Next Number ***");
        MiddleTextbottom.setText("Connecting to the database for Table Variables");

        String query01="SELECT MAX(number)+1 FROM `Loads` WHERE month = 'Jan' AND `date_arrived` BETWEEN '2018-01-01' AND '2018-12-31'";
        String query02="SELECT MAX(number)+1 FROM `Loads` WHERE month = 'Feb' AND `date_arrived` BETWEEN '2018-01-01' AND '2018-12-31'";


        ps =  con.prepareStatement(query01);
        ps2 = con.prepareStatement(query02);
        rs = ps.executeQuery();
        rs2 = ps2.executeQuery();

        while(rs.next()){
           query01 = rs.getString(1);

            if (rs.getString(ICONIFIED) ==null) {
                Main.UpdatedNextjan18.setText(query01);
                Main.UpdatedNextjan18.setText("1");
            }else{
                Main.UpdatedNextjan18.setText(query01);
            } 


        while(rs2.next()){
           query02 = rs2.getString(1);
            if (rs2.getString(ICONIFIED) ==null) {
                Main.UpdatedNextfeb18.setText(query02);
                Main.UpdatedNextfeb18.setText("1");
            }else{
                Main.UpdatedNextfeb18.setText(query02);
            } 

        }
        }


    } catch (ClassNotFoundException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println("Error: "+ex);
    } catch (SQLException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println(ex);
    }catch ( java.util.NoSuchElementException ex) {
          Logger.getLogger(SQLLoads.class.getName()).log(Level.SEVERE, null, ex);
          System.out.println("Error: "+ex);

    }
    con.close();
    return null;

        }

Java帮助-MySQL-SQLConnector“无限递归”并且控制台打印无限

1 个答案: