com.mysql.cj.jdbc.exceptions.CommunicationsException：通信链接失败

Question

i am trying to connect my java app with sql database and when i click on save button it gives me following error

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

here's my code

        name = full_name_input.getText();
        Fname = father_name_input.getText();
        cnic = father_cnic_input.getText();
        DOB = Integer.parseInt(DOB_input.getText());
        Class_V = Integer.parseInt(class_input.getText()); 
        prsnt_add = present_add_input.getText();
        city = city_input.getText();
        province = radio_text;
        Connection conn = null;
        PreparedStatement pst = null;

        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql:///UserDetails", "root", "sahanj");
            pst = conn.prepareStatement("insert into UserDetails values (?,?,?,?,?,?,?,?)");

            pst.setString(1, name);
            pst.setString(2, Fname);
            pst.setString(3, cnic);`enter code here`
            pst.setInt(4, DOB);
            pst.setInt(5, Class_V);
            pst.setString(6, prsnt_add);
            pst.setString(7, city);
            pst.setString(8, province);

            int x = pst.executeUpdate();

            if (x>0)
            {
                JOptionPane.showMessageDialog(null, "Record Saved !\n");
            }
            else
            {
                JOptionPane.showMessageDialog(null, "Data Not Saved !\n");
            }
        }

        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null, e);
        }
}                                  

Answer 1

This error generally occur because of following reason. 1.hostname in JDBC URL is not correct. 2.port number is not correct. 3.db server is not up. for these take following step 1. give full JDBC url or test with ping. 2. check in my.cnf of mysql. 3. start the db.