While you may have a strong foundation in Java I/O, real-world applications often demand high-level APIs that simplify code and improve readability. In this chapter, we explore modern Java APIs that help you do more with less code, especially improvements introduced since Java 8.

• Reading and writing text files
• Reading text, images, JSON from the web
• Visiting files in a directory
• Reading ZIP files as file systems
• Creating temporary files and directories

This chapter focuses on practical, modern I/O features using java.nio.file.Files, java.net.http.HttpClient, and related classes.

• Java 18+: UTF-8 is the default charset (JEP 400)
• Files API: Expanded significantly since Java 7 with new methods in Java 8, 11, and 12
• InputStream now includes readAllBytes, transferTo, etc.
• java.io.File and BufferedReader are considered outdated

Path path = Path.of("/usr/share/dict/words");
String content = Files.readString(path); // Reads the whole file

Read as lines:

List<String> lines = Files.readAllLines(path);

Process lazily with streams:

try (Stream<String> lines = Files.lines(path)) {
    lines.forEach(System.out::println);
}

Stream<String> tokens = new Scanner(path).useDelimiter("\\PL+").tokens();

Files.writeString(path, content);
Files.write(path, List.of("line1", "line2"));

Using PrintWriter (for formatted output):

try (PrintWriter writer = new PrintWriter(path.toFile())) {
    writer.printf(locale, "Hello, %s!", name);
}

Using BufferedWriter:

try (BufferedWriter writer = Files.newBufferedWriter(path)) {
    writer.write("Hello");
    writer.newLine();
}

InputStream in = new URI("https://example.com").toURL().openStream();
String result = new String(in.readAllBytes());

Using Jackson (JSON):

Map<String, Object> result = JSON.std.mapFrom(new URI("https://api").toURL());

Reading image:

BufferedImage img = ImageIO.read(new URI(imageUrl).toURL());

List files:

try (Stream<Path> entries = Files.list(path)) {
    entries.forEach(System.out::println);
}

Walk recursively:

try (Stream<Path> entries = Files.walk(path)) {
    entries.filter(p -> p.toString().endsWith(".html"))
           .forEach(System.out::println);
}

Use Files.find() for attribute-based filtering.

Mount ZIP file as a virtual file system:

try (FileSystem zipFs = FileSystems.newFileSystem(pathToZip)) {
    Files.walk(zipFs.getPath("/"))
         .filter(Files::isRegularFile)
         .forEach(System.out::println);
}

Path tempFile = Files.createTempFile("prefix", ".tmp");
Path tempDir  = Files.createTempDirectory("prefix");

These are deleted automatically on reboot or can be managed manually.

Modern Java I/O is simpler, more powerful, and safer:

• Use Files.readString, Files.writeString, and Files.walk instead of old APIs.
• Prefer high-level classes and built-in charset handling (UTF-8).
• Avoid legacy File and BufferedReader where possible.
• Explore the full power of the Files and Path APIs.