8.4 Directories, Encoding, and File Management

Many file bugs come from the "around the file" details: the path is not where you think, the parent folder does not exist, the encoding is different, or a file-management operation overwrites important data.

Relative Paths and the Current Working Directory

A relative path is not automatically relative to the Java source file. It is relative to the current working directory, usually the directory where you run java.

Path path = Path.of("data", "quotes.txt");
String content = Files.readString(path, StandardCharsets.UTF_8);

If the current working directory is the project root, Java looks for:

project/
  data/
    quotes.txt

But if you run the program from another directory, the same relative path may not be found.

Creating Directories

Writing reports/summary.txt fails if reports does not exist. Create parent directories first.

Path folder = Path.of("reports");
Files.createDirectories(folder);

Path report = folder.resolve("summary.txt");
Files.writeString(report, "Report ready" + System.lineSeparator(), StandardCharsets.UTF_8);

createDirectories() is different from "create one folder only." It creates missing parent directories too, and it does nothing if the directory already exists.

UTF-8 Encoding

Text files store bytes. Encoding converts between characters and bytes. UTF-8 is one of the most common and compatible text encodings.

Path path = Path.of("note.txt");
Files.writeString(path, "Hello, Java!", StandardCharsets.UTF_8);
System.out.println(Files.readString(path, StandardCharsets.UTF_8));

If writing and reading use different encodings, plain English may appear fine, but non-English text and symbols can break. Use StandardCharsets.UTF_8 in examples unless you have a specific reason not to.

Listing, Copying, Moving, and Deleting

Files can inspect and manage files:

Path path = Path.of("note.txt");

System.out.println(Files.exists(path));
System.out.println(Files.size(path));
System.out.println(Files.isRegularFile(path));

Directory listing uses a stream, which must be closed. Try-with-resources handles that.

try (var entries = Files.list(Path.of("reports"))) {
    entries.forEach(System.out::println);
}

Common management methods:

• Files.copy(source, target): copy a file.
• Files.move(source, target): move or rename a file.
• Files.delete(path): delete and fail if the file does not exist.
• Files.deleteIfExists(path): delete only when present.

These operations can overwrite, fail, or remove data. Treat them with care.