Htykuut

Im trying to create web app using java and mariadb but i encountered problem when tried to implement mariadb to login. Here my code:

initSql:
package dao;

import java.sql.Connection;

import java.sql.DriverManager;



import javax.servlet.ServletConfig;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;





@WebServlet("/initSql")

public class initSql extends HttpServlet {

private static final long serialVersionUID = 1L;



/**

 * @see HttpServlet#HttpServlet()

 */

public initSql() {

    super();

    // TODO Auto-generated constructor stub

}



/**

 * @see Servlet#init(ServletConfig)

 */

Connection conn = null;

public void init(ServletConfig config) throws ServletException {

    // TODO Auto-generated method stub

    try {

        Class.forName("org.mariadb.jdbc.Driver");

        Connection conn = DriverManager.getConnection("jdbc:mariadb://localhost:3306/baza_new", "root","root");

        System.out.println("db povezana");



    }catch(Exception e){

        //JOptionPane.showMessageDialog(null, e);

        System.out.println("db NIiiJE povezana");

        //return null;

}



}

}   

LoginDAO:

    package dao;



    import java.sql.Connection;

    import java.sql.PreparedStatement;

    import java.sql.ResultSet;

    import dao.initSql;



    public class LoginDAO {



    static Connection con = null;



    public static boolean validate(String username, String password, String type) {



        boolean status = false;

        try {

            con = initSql.init();

            System.out.println("1");

            String query = "select * from users where username=? and password=?";

            PreparedStatement pst = con.prepareStatement(query);



            //pst.setString(1, type);

            pst.setString(1, username);

            pst.setString(2, password);



            ResultSet rs = pst.executeQuery();

            status= rs.next();

            con.close();    

        }catch(Exception e) {System.out.print(e);}



        return status;      

    }   

}

and i get markers:
Cannot make static reference to non-static method from type generic servler
Type mistmatch cannot connect from void to Connection
I'm little bit stuck with this problem.Can someone help me with my code?

People seem to be neglecting the more broad-scale issues in your code. There are standards to follow like capitalization etc but overall you have some bigger issues.

You shouldn't be making erroneous instances of initSql as it's an HttpServlet, it just doesn't make sense. You also have static/non-static references to a Connection field when you don't need it. To start with, change initSql#init to return a Connection, and while I normally wouldn't recommend abusing static this way, make the method itself static:

//returns a connection, requires no class instance

public static Connection init(ServletConfig config) { ... }

From there, we can now retrieve a Connection instance by calling this method:

Connection con = initSql.init();

Overall you should have a proper class or design for handling this, but for simple learning this is "okay".

Secondly, you're not quite using ResultSet correctly. #next will determine if there is an available row to point to from the SQL results, and if so it moves the marker to the next row. You would use it in order to check if you can retrieve results:

ResultSet set = /* some sql query */;

String someField;

if (set.next()) {

    //gets the value of the column "my_field"

    someField = set.getString("my_field");

} else {

    //no results!

    someField = null;

}

Alternatively, if you were looking for multiple results you can loop over #next

while (set.next()) {

    //just one value out of many

    String myField = set.getString("my_field");

}

In this use-case it's alright to check if the row exists, but I would personally check against something like user permissions or somesuch. If you relied on code like this for something sensitive you might expose something you don't want to.

Overall, I would work a little more on your logical structure for the code, and maybe go over some of the basics for Java and common coding standards for it (Google and Oracle have good guides for this).

Firstly, your class name initSql should have Capitalized first letter to follow conventions.

Secondly, you should either create an instance/object of InitSql and then call the method init() on that object or make the init() method static.

initSql.init() isn't static, which is not a problem of MariaDB and its connection from Java :) To fix this error you can add static to the mentioned method. But: As there are multiple errors in your code (e.g. assigning the result of a void method to a variable), it will not work then either..