Java NIO 파일 작업 (원본)

Java NIO File Operations

Comprehensive guide to Java NIO file I/O operations using java.nio.file.Path and java.nio.file.Files APIs.

Core Concepts

Path Creation and Resolution

Path creation methods:

• Paths.get("path/to/file") — Java 7+
• Path.of("path/to/file") — Java 11+ (shorthand for Paths.get())

Common Path operations:

Path p1 = Paths.get("some/folder/file.txt");
Path resolved = p1.resolve("child.txt");   // Append to path
Path parent = p1.getParent();              // Get parent directory
Path fileName = p1.getFileName();          // Get filename only
Path abs = p1.toAbsolutePath();            // Convert to absolute path
Path normalized = p1.normalize();          // Clean up "." and ".." segments

File Existence and Type Checking

Files.exists(path)           // File exists
Files.notExists(path)        // File does not exist
Files.isDirectory(path)      // Is directory
Files.isRegularFile(path)    // Is regular file

File Creation

Directory Creation

Files.createDirectory(path)    // Single level, throws if parent missing
Files.createDirectories(path)  // Creates parent dirs as needed, safest option

File Creation

Files.createFile(path)  // Creates empty file, throws FileAlreadyExistsException if exists

Best practice: Check existence first or handle exception appropriately.

File Reading

Java 11+ (Simplest)

String content = Files.readString(path);  // Read entire file as String

Java 8+ (Compatible)

String content = new String(Files.readAllBytes(path), StandardCharsets.UTF_8);
List<String> lines = Files.readAllLines(path);  // Read as List<String>

Large Files (Stream-based)

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

File Writing

Java 11+

Files.writeString(path, "content");  // Overwrite existing file
 
// Append mode
Files.writeString(path, "content", 
    StandardOpenOption.CREATE, StandardOpenOption.APPEND);

Java 8+

Files.write(path, content.getBytes(StandardCharsets.UTF_8));
Files.write(path, linesList, StandardOpenOption.CREATE);

File Operations

Copy/Move/Delete

Files.copy(src, dest, StandardCopyOption.REPLACE_EXISTING);
Files.move(src, dest, StandardCopyOption.REPLACE_EXISTING);
Files.delete(path);           // Throws if file doesn't exist
Files.deleteIfExists(path);   // Returns false if doesn't exist, safer

Directory Traversal

List Directories (One Level)

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

Recursive Walk

try (Stream<Path> stream = Files.walk(dir)) {
    stream.filter(Files::isRegularFile)
          .forEach(System.out::println);
}

Search with Pattern

try (Stream<Path> stream = Files.find(dir, Integer.MAX_VALUE,
        (p, attr) -> p.toString().endsWith(".txt"))) {
    stream.forEach(System.out::println);
}

File Information

long size = Files.size(path);                    // File size in bytes
FileTime modified = Files.getLastModifiedTime(path);  // Last modified timestamp

Java Version Differences

Key Java 11+ Additions

• Path.of() — Shorthand for Paths.get()
• Files.readString() — Direct string reading
• Files.writeString() — Direct string writing

Java 8 Compatibility

• Use Paths.get() instead of Path.of()
• Use Files.readAllBytes() + new String() for text reading
• Use Files.write() with byte arrays for text writing

Best Practices

1. Resource Management: Always use try-with-resources for streams

   try (Stream<String> lines = Files.lines(path)) {
       // Process lines
   }

2. Exception Handling: Choose between exception-throwing vs safe methods

   • Files.createFile() throws if exists → Check Files.exists() first
   • Files.delete() throws if missing → Use Files.deleteIfExists()

3. Encoding: Always specify character encoding for text files

   Files.readString(path, StandardCharsets.UTF_8)

4. Options: Use StandardOpenOption for write behavior control

   • CREATE — Create if doesn’t exist
   • APPEND — Append to existing file
   • TRUNCATE_EXISTING — Overwrite existing content

References

• java-io — Java I/O operations overview
• java-streams — Java Stream API usage