我怎样才能使用相对文件名而不是绝对文件名？

Question

I am having my program read a .txt file and I don't want to use the absolute file name because it is machine dependent and I just want to use the relative file name. I don't know how to get it to do that. Here is the part of my program I am talking about:

private List<String> readFile() {

    List<String> wordsList = new ArrayList<>();

    try {
        String fileName = "C:/Users/Phil/Documents/FourLetterWords.txt";
        File fourLetterWords = new File(fileName);
        Scanner in = new Scanner(fourLetterWords);

        while (in.hasNextLine()) {
            String line = in.nextLine();
            if (line!=null && !line.isEmpty()) {
                wordsList.add(line);
            }
        }
    } 
    catch (FileNotFoundException ex) {
        System.out.println("File not found.");
    }
    return wordsList ;
}

If I were to make it just:

"C:/FourLetterWords.txt"

then my catch exception comes in and says File not found. But I really just want to use...

"FourLetterWords.txt"

Answer 1

Change this

String fileName = "C:/Users/Phil/Documents/FourLetterWords.txt";

to something like

File f = new File(System.getProperty("user.home"),
    "Documents/FourLetterWords.txt");

which will work to get the "user.home" on every platform that Java supports, and then append "Documents/FourLetterWords.txt" to that path.

Answer 2

you can either

1. pass the filename as an parameter
2. You can load files from the same directory as the .class file with getResourceAsStream().
3. System.getProperty("user.dir") returns the current directory

Answer 3

What they said, plus here's some additional useful tricks for navigating up and down folder levels:

//absolute path from where application has initialized
String target = System.getProperty("user.dir"); 

//drop the last folder to go down one level
target = target.substring(0, target.lastIndexOf(File.separator)); 

//go into another directory
target = target + File.separator + targetFolder; 

//use it
return target;

Answer 4

Using relative file paths has to do with the path you are currently in. Just guessing here, but try "Documents/FourLetterWords.txt".

If that works, the reason is because your current directory is "C:\\Users\\Phil"

if not try

System.out.println("Working Directory = " + System.getProperty("user.dir"));

then try moving the file there to be able to use "FourLetterWords.txt".

Answer 5

There are 2 scenarios for file access in Java or any programming language:

a. The file is present with in the project directory.
b. File is out of the project directory.

File is present bundled or pushed to folder in project directory. In this case you could use some thing like
String fileName = "/resourceFolder/FourLetterWords.txt";

The resource folder is child of the root folder of the project.

You need to have a property set, which will always have the path where you will be having the file. You need to set it as part of the env so that the code will always run on all operating systems. You can also set it as part of the property file which will be changing for each operating system.

Getting system variable: System.getEnv("FILE_DIR");
Getting property: System.getProperty("file.dir");