[SQL] How to check if entered value is equal to a value in a SQL database?

I have a database with 7 rows, and 4 columns in each. I am prompting an user to enter a code, and I need to cross reference the database to see if the entered code equals one of the codes in the database (first column in each row).

At first, I was checking if the result set came up as null, but that was not working. I was trying if(rs.wasNull()), but it never seemed to execute.

Does anybody have any advice on what to look at to solve my issue? Here's a code snippet if helps at all.

if(!rs.wasNull()) {
while(rs.next()) {
Products temp = new Products(rs.getString(1), rs.getString(2), rs.getDouble(3), rs.getBoolean(4));
productsList.add(temp);
// For testing purposes
//out.println(temp.toString());
request.setAttribute("productsList", productsList);
request.getRequestDispatcher("Scan.jsp").forward(request, response);
}
}

else if(rs.wasNull()) {
Products wrongCode = null;
productsList.add(wrongCode);
request.setAttribute("productsList", productsList);
request.getRequestDispatcher("Scan.jsp").forward(request, response);
}


EDIT: I now know that ResultSet never returns null. It will return an empty ResultSet.

EDIT 2: I've wrote this method to solve the problem:

public boolean codeExists(int code) {
final String SELECT_QUERY = "SELECT * FROM productcatalogue WHERE code = ?";
try {

PreparedStatement statement = conn.prepareStatement(SELECT_QUERY); // Create query statement
statement.setInt(1, code);

ResultSet queryResult = statement.executeQuery();
if (!queryResult.next()) { // Check if code entered exists
return false; // Tells that the author doesn't exist
}
} catch (SQLException sqlException) {

sqlException.printStackTrace();

}
return true; //Otherwise the item exists
}

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