JAR 的输入文件

Question

I want to send the input of a jar from one file and save the output in another,

public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        List<String> builder = new ArrayList<>();
        String line;
        while (!(line = sc.nextLine()).isBlank()) {
            builder.add(line);
        }
        builder.stream().sorted().forEach(System.out::println);

        sc.close();
} 

when I execute the jar I try it like this

java -jar name.jar > output.txt < input.txt

but it generates the exception java.util.NoSuchElementException, I appreciate any help.

Answer 1

This is what I believe is the easiest way to accomplish what you are trying to do:

    public static void main(String[] args) throws IOException {
        FileWriter fw = new FileWriter("output.txt"); // Used to write to output.txt
        Scanner sc = new Scanner(System.in);
        List<String> builder = new ArrayList<>();

        while (sc.hasNextLine()) { // Same thing as what you had, just 1 less line
            // Not entirely sure what you're trying to do here;
            //if no input is given at the EXACT time the program is run, this will be skipped
            builder.add(sc.next());
        }

        builder.stream().sorted().forEach((s) -> { // Changed this to a lambda
            System.out.println(s);
            try {
                fw.write(s);
            } catch (IOException e) {
                e.printStackTrace();
            }
        });

        fw.close();
        sc.close();
    }

Answer 2

The easiest way would be to pass your input.txt file as a parameter to your jar. You can then utilize Files.readAllLines to read your text file and do your sort and then send each line to std out

Then you can redirect std out to your output.txt file.

public static void main(String[] args) throws IOException {
    
  if (args == null || args.length == 0) throw new RuntimeException("No file provided");
    
  Path file = Paths.get(args[0]);
    
  if (Files.notExists(file)) throw new IOException(args[0] + " cannot be found.");
    
  Files.readAllLines(file).stream().sorted().forEach(System.out::println);
    
}

Then you can invoke it like this:

java -jar name.jar input.txt > output.txt

Answer 3

The code is okay, not perfect, but it works. Of course your class needs to have some more lines (like defining the import and class definition etc.), but you only posted the main method is and that's okay for me.

At runtime, you're piping < input.txt as your standard input which is great.

I think your problem could be:

• Your input.txt contains nothing, then you'll get this exception
• Or the input.txt is in a different directory at runtime, so you're actually not piping anything as an input. There's no error from the command line, but this way you get the exception too.

One of those could be the cause.