No suitable driver found for jdbc:sqlserver://x.x.x.x

Question

I'm trying to expose this function as web service,my function show all the databases in a host and i got this error,i'm trying to connect to microsoft sql server. Any idea where i'am wrong.

public List<String> connexion(){
             Connection conn = null;
            List <String> listdb= new ArrayList<>();
            listdb.add("ok");
        try {

             String dbURL = "jdbc:sqlserver://x.x.x.x\\sqlexpress";
             String user = "xxx";
             String pass = "xxx";
             conn = DriverManager.getConnection(dbURL, user, pass);
             if (conn != null) {
                 DatabaseMetaData dm = (DatabaseMetaData) conn.getMetaData();
                 System.out.println("Driver name: " + dm.getDriverName());
                 System.out.println("Driver version: " + dm.getDriverVersion());
                 System.out.println("Product name: " + dm.getDatabaseProductName());
                 System.out.println("Product version: " + dm.getDatabaseProductVersion());
                 ResultSet rs = conn.getMetaData().getCatalogs();

                 while (rs.next()) {
                     listdb.add(rs.getString("TABLE_CAT"));
                     System.out.println("TABLE_CAT = " + rs.getString("TABLE_CAT") );
                     return listdb;

                 }
                 return listdb;
             }

         } catch (SQLException ex) {
             ex.printStackTrace();
         } 
        finally {
             try {
                 if (conn != null && !conn.isClosed()) {
                     conn.close();
                 }
             } catch (SQLException ex) {
                 ex.printStackTrace();
             }

    }
        return listdb;

    }