Java与Eclipse的JDBC连接（当方法调用方法时）

Question

I'm trying to connect to my DB using JDBC. I wanted to make a method for connection and another method for selecting data. I am getting a red line in Eclipse on the 'Connection con = connectDB();' part. ( See also attached) Cany anyone give me advice?

public class DBJdbc {

 //Statement stmt = null;

// connecting to DB
public void connectDB() {            

    //Connection con = null;

    try { 
        Class.forName("com.mysql.cj.jdbc.Driver"); 

        Connection con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "***", "***");
    }
    catch(SQLException e) { 
        e.printStackTrace();
    }
    catch(ClassNotFoundException e) {
        e.printStackTrace();
    }


}   

// a method for selecting DB
public static  void select() { 

    //connectDB(); 

    String sql = "SELECT * from SAC_SUR";

        try(Connection con = connectDB();  // I'm getting a red line here) 
            PreparedStatement pstmt = con.prepareStatement(sql)){
            Statement stmt = con.createStatement(); 
            ResultSet rs = stmt.executeQuery(sql);
            while(rs.next()) {
                int id = rs.getInt(1);
                String name = rs.getString(2);
                System.out.println("Id = " + id + "name = " + name);
            } //while 
        } catch(SQLException e) {
            System.out.println(e.getMessage());
        }
}   

red line here!!!

Answer 1

connectDB() method is of void type and not returning anything but when you are calling the method, you are assigning it to variable con. So you need to change the return type of connectDb to the Connection type.

public Connection connectDB() {            

    Connection con = null;

    try { 
        Class.forName("com.mysql.cj.jdbc.Driver"); 

         con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "***", "***");
    }
    catch(SQLException e) { 
        e.printStackTrace();
    }
    catch(ClassNotFoundException e) {
        e.printStackTrace();
    }

return con;
}  

Answer 2

You are trying to call non-static method into the static area, which is not allowed in Java. So I made this method static and returning the database connection.

Please update the below method into your code. It will resolve your problem.

public static Connection connectDB() { 
    Connection con = null; 
    try { 
        Class.forName("com.mysql.cj.jdbc.Driver"); 
        con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "", ""); 
    } catch(SQLException e) { 
        e.printStackTrace(); 
    } catch(ClassNotFoundException e) { 
        e.printStackTrace(); 
    } 
    return con; 
}