How to get String array using Files.list()

Question

I have a txt file with strings.

I want to get a String array containing all lines from the file via Files.list(Paths.get("path")) method.

I tried to use toArray() but it returns an array of paths to files in "path" directory

How can I get it using Files.list(Paths.get("path")) (it's mandatory)?

I have something like this:

public Object[] returnStrings(){
    Object[] strings;
    try {
        strings = Files.list(Paths.get(path)).toArray();
    }catch (IOException ex){
        return null;
    }
    return strings;
}

Answer 1

Files.list() expects a path pointing to the directory as a parameter, and it'll give you a stream of Path objects (if any) contained in this directory. In case if the given path will be a file, you will get a NotDirectoryException exception. You can't access the contents of a file with Files.list(), it's simply meant for another purpose.

In order to read from the text file you can use either Files.lines() or Files.readAllLines().

Contrary to Files.readAllLines() which dumps all file content into memory, the stream produced by Files.lines() will be populated lazily. Hence, in a general case Files.lines() a preferred way to read from a file, especially when you're unaware of it's size.

For this task, even though all file's content has to be allocated in the memory (i.e. in this case the mentioned above upper-hand of a stream's laziness isn't important), Files.lines() is a better choice because the expected result needs to be an array of strings. It will be both more performant and more space-efficient to generate an array as a result of execution of the stream pipeline, rather than reading the file into a list (which readAllLines() returns) and then creating a string array based on this list.

With Files.lines() it could be implemented like that:

public static String[] readFromFile(Path path) {
    String[] result;
    try(Stream<String> stream = Files.lines(path)) {
        result = stream.toArray(String[]::new);
    } catch (IOException e) {
        result = new String[0];
    }
    return result;
}

There are several important issues in your code:

• You are not closing the resource. Because stream is accessing the file, it has to be closed either explicitly inside the finally block or by using try with resources, as shown above (which preferred and more concise way).
• It not a good idea to store String in the array of Objects because in order to do anything with these strings apart from printing them you will have to do an unsafe type casting.
• It not very nice to return null in case when attempt to read from the file fails. Because null can a cause a problem afterwards when it'll not be obvious where it came from.

And lastly, a few recommendations:

• Avoid placing the return statement inside the try and catch blocks, it reduces readability.
• List is more convent and flexible container of data than array. In cases when you are not dealing with an existing code that expects an array, use List instead.