JDBC错误“连接过多”

Question

I have created a java swing application in which basically user logs in gets to the main window and select a jmenu item which leads the user to a new window where you can input data to the database.

In this 3rd window where the data base is updated, i have used a jcombobox where the items in it are loaded from the database.

when i debug it, it runs properly. But when I try to run the application top to bottom, the updating window is displayed but the jcombobox items are not being loaded. it gives an error saying too many connections.

as far as my knowledge, ive closed all the connections properly.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
String un=jTextField1.getText();
String pwd=jPasswordField1.getText();
   if(un.isEmpty()){
       JOptionPane.showMessageDialog(this,"User Name is empty");
   }
   else  if(pwd.isEmpty()){
       JOptionPane.showMessageDialog(this,"Password is empty");
   }
   else{
    try {
         DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd hh:mm:ss");
        Calendar cal = Calendar.getInstance();

        ResultSet rs=new DBconnect().getdata("SELECT * FROM user");
        rs.next();
        if ((rs.getString("Name").equals(un))&&(rs.getString("pw").equals(pwd))){
            new DBconnect().putdata("INSERT INTO login (Date,User) VALUES('"+dateFormat.format(cal.getTime())+"','"+un+"')");
          new  MainWindow().setVisible(true);

          this.dispose();
        }
        else{
            JOptionPane.showMessageDialog(this, "Invalid user name or password");
            jTextField1.setText("");
            jPasswordField1.setText("");
        }
        rs.close();
    } catch (Exception ex) {
        Logger.getLogger(Login.class.getName()).log(Level.SEVERE, null, ex);
    }

   }
}                                        

above is my login forms code.

 public MainWindow() {
    setExtendedState(JFrame.MAXIMIZED_BOTH);
    new Thread(){
        public void run(){
            while(true){
       DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
       Calendar cal = Calendar.getInstance();

       DateFormat dateFormat2 = new SimpleDateFormat("yyyy/MM/dd");
       Calendar cal2 = Calendar.getInstance();

       jLabel1.setText(dateFormat.format(cal.getTime()));

                try {
                    ResultSet rs=new DBconnect().getdata("SELECT COUNT(Pno) FROM medicalhistory WHERE Date ='"+dateFormat2.format(cal2.getTime())+"'");
                    rs.next();
                    jLabel4.setText(rs.getString("COUNT(Pno)").toString());


                    ResultSet rs2=new DBconnect().getdata("SELECT SUM(Amount) FROM income WHERE Date ='"+dateFormat2.format(cal2.getTime())+"'");
                    rs2.next();
                    jLabel5.setText(rs2.getString("SUM(Amount)").toString());
                    rs2.close();
                    rs.close();

                } catch (Exception ex) {
                    Logger.getLogger(MainWindow.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    }.start();


    initComponents();
}

above is the main windows' code where ive used connections. these work properly.

public addnewpatient() {
            setExtendedState(JFrame.MAXIMIZED_BOTH);


    initComponents();
        try {
                try (ResultSet rs3 = new DBconnect().getdata("SELECT Name FROM drugstock WHERE stockAmount >0")) {
                    Vector v= new Vector();
                    while(rs3.next()){
                        String ids = rs3.getString("Name");
                        v.add(ids);
                        jComboBox1.addItem(ids);
                    }
                    jComboBox1.addItem("Null");
                  rs3.close();
                }

    }


        catch (Exception ex) {
        Logger.getLogger(addnewpatient.class.getName()).log(Level.SEVERE, null, ex);
    }
}

above code gives the too many connections error.

putdata and getdata are two methods ive created in the connection class for easiness.

:) Thanx in advance :)

Answer 1

I can see you are creating connections in below line :

ResultSet rs3 = new DBconnect().*;

Then you are just closing ResultSet - rs3.close();

Who takes care of closing your database connections and how?

How to fix now:

There is no need of internal try block in you code - so remove it.

Getting connection :

DBconnect dbconnect = new DBconnect();
ResultSet rs3 = dbconnect..getdata("...");;

Before exiting try block - close ResultSet, Connection.

rs3.close();
dbconnect.close();

Replace your DBConnect.java as below:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;

public class DBconnect {
    static String url = "jdbc:mysql://localhost:3306/ppmgt";
    Connection conn;
    Statement st;

    public DBconnect() {

        try {
            Class.forName("com.mysql.jdbc.Driver");
            this.conn = DriverManager.getConnection(url, "root", "");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void putdata(String sql) throws Exception {
        st = this.conn.createStatement();
        st.executeUpdate(sql);
    }

    public ResultSet getdata(String sql) throws Exception {
        Statement st = this.conn.createStatement();
        return st.executeQuery(sql);
    }

    public void close() {
        try {
            this.conn.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static long compareTo(Date date1, Date date2) {
        return date1.getTime() - date2.getTime();
    }
}

There are no other changes needed in classes using DBconnect class other than closing connection:

dbconnect.close();

Answer 2

public class DBconnect {
static String url = "jdbc:mysql://localhost:3306/ppmgt";



public static Connection con() throws Exception {
    Class.forName("com.mysql.jdbc.Driver");
    Connection c = DriverManager.getConnection(url, "root", "");
    return c;
}

public void putdata(String sql) throws Exception {
    Connection c = DBconnect.con();
    Statement st = c.createStatement();
    st.executeUpdate(sql);

}

public ResultSet getdata(String sql) throws Exception {
    Connection c = DBconnect.con();
    Statement st = c.createStatement();
    ResultSet r = st.executeQuery(sql);

    return r;
}

    public static long compareTo(Date date1,Date date2) {
    return date1.getTime() - date2.getTime();
}

}

this is my DBconnect class