What is not working?

public static void main(String[] args) throws Exception {
    if (args.length < 2) return;

    String fileName;
    try (BufferedReader console = new BufferedReader(new InputStreamReader(System.in))) {
        fileName = console.readLine();
    }

    switch (args[0]) {
        case "-u":
            updateProduct(fileName, args);
            break;
        case "-d":
            deleteProduct(fileName, args[1]);
            break;
    }
}

private static void updateProduct(String fileName, String[] args) throws IOException {
    List<String> products = readProductList(fileName);

    try {
        long needle = Long.parseLong(args[1]);
        int index = findProduct(products, needle);

        products.set(index, String.format("%-8d%-30s%-8s%-4s", needle, args[2], args[3], args[4]));
        writeProductList(fileName, products);
    } catch (ProductNotFoundException ignored) { }
}

private static void deleteProduct(String fileName, String needle) throws IOException {
    List<String> products = readProductList(fileName);

    try {
        int index = findProduct(products, Long.parseLong(needle));

        if (products.remove(index) != null)
            writeProductList(fileName, products);
    } catch (ProductNotFoundException ignored) { }
}

private static int findProduct(List<String> products, long needle) throws ProductNotFoundException {
    for (int i = 0; i < products.size(); i++) {
        String line = products.get(i);
        if (Long.parseLong(line.substring(0, 8).trim()) == needle) {
            return i;
        }
    }
    throw new ProductNotFoundException();
}

private static void writeProductList(String fileName, List<String> products) throws IOException {
    Files.write(Paths.get(fileName), products);
}

private static List<String> readProductList(String fileName) throws IOException {
    return Files.readAllLines(Paths.get(fileName));
}

private static class ProductNotFoundException extends Exception {}

public static void main(String[] args) throws IOException {
   if(args.length==0) return; // no args end program

   // #1 gets filename
   BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
   String fileName = reader.readLine();
   reader.close(); // close

   args[1] = args[1].trim(); // removes spaces if they exist in ags[1] for later comparison

   List<String> products = new ArrayList<>();
   String product = null;
   BufferedReader fileReader = new BufferedReader(new FileReader(fileName));

   // reads all products. Will update or delete when an ID matches depending on args[0]
   while(fileReader.ready()) {
      product = fileReader.readLine();
      if(args[1].equals(product.substring(0,8).trim())){ // checks if ID of product and args[1] match
         if(args[0].equals("-d")) continue; // skips if args[0] = '-d' (effectively deletes product)
         else if(args[0].equals("-u")) // otherwise if args[0] = '-u' it replaces product
            product = String.format("%-8s%-30s%-8s%-4s", args[1], args[2], args[3], args[4]);
      }
      products.add(product); // adds product to list for writing back to file later
   }
   fileReader.close(); // close

   int i = 0;
   FileWriter fileWriter = new FileWriter(fileName);

   fileWriter.write(products.get(i)); // write first product
   while(++i < products.size())
      fileWriter.write("\n" + products.get(i)); // writes each additional with newline then product (no new line at the end of file)
   fileWriter.close(); // close
}

public static void main(String[] args) throws IOException {

   if(args.length==0) return;
   args[1] = args[1].trim();  // ← this line

   // rest of code
}

switch(args[0]){
            case "-u": // update
                for(Product product : products){
                    if(String.valueOf(product.id).equals(args[1])){
                        String name = args[2].length() > 30? args[2].substring(0, 30).trim():args[2].trim();
                        String price = args[3].length() > 8? args[3].substring(0, 8).trim():args[3].trim();
                        String quantity = args[4].length() > 4? args[4].substring(0, 4).trim(): args[4].trim();
                        product.setProductName(name);
                        product.setPrice(price);
                        product.setQuantity(quantity);
                    }
                }
                break;
            case "-d": // delete
                Iterator<Product> itr = products.iterator();
                while(itr.hasNext()){
                    Product product = itr.next();
                    if(String.valueOf(product.id).equals(args[1])){
                        products.remove(product);
                        break;
                    }
                }
                break;
        }
        FileWriter fileWriter = new FileWriter(fileName);
        for(Product product : products){
            fileWriter.write(product.toString());
            fileWriter.write("\n");
        }
        fileWriter.close();