java.sql.SQLException: Invalid column name ERROR

I am passing a string parameter to a java method to get a particular object from the db. Faced some trouble when passing the parameter to the SQL string.

    //SELECT a Product
public static Product searchProduct (String productId) throws SQLException, ClassNotFoundException {
    //Declare a SELECT statement
    String selectStmt = "SELECT * FROM product WHERE id = '"+ productId +"'";

    //Execute SELECT statement
    try {
        //Get ResultSet from dbExecuteQuery method
        ResultSet rsEmp = DBUtil.dbExecuteQuery(selectStmt);

        //Send ResultSet to the getProductFromResultSet method and get product object
        Product product = getProductFromResultSet(rsEmp);

        //Return product object
        return product;
    } catch (SQLException e) {
        System.out.println("While searching an product with '" + productId + "' id, an error occurred: " + e);
        //Return exception
        throw e;
    }
}

It occurs the above error. The column is there and the dbQuery also working fine. The query also looks fine.

SELECT * FROM product WHERE id = 'G002'

Where could I go possibly wrong?

The table structure:

+-------------+--------------+------+-----+---------+-------+
| Field       | Type         | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| id          | varchar(20)  | NO   | PRI | NULL    |       |
| title       | varchar(200) | YES  |     | NULL    |       |
| type        | varchar(200) | YES  |     | NULL    |       |
| description | varchar(200) | YES  |     | NULL    |       |
| unit_price  | varchar(20)  | YES  |     | NULL    |       |
| quantity    | varchar(20)  | YES  |     | NULL    |       |
+-------------+--------------+------+-----+---------+-------+