Java 7引入的NIO.2java.nio.file大幅简化了文件操作。本文讲解Path、Files、WatchService、内存映射文件等高级用法。一、Path与Filesjava复制下载import java.nio.file.*; Path path Path.of(/tmp/data.txt); // 或 Paths.get(/tmp/data.txt) System.out.println(path.getFileName()); System.out.println(path.getParent()); System.out.println(path.toAbsolutePath()); // 文件操作 Files.exists(path); Files.createFile(Path.of(/tmp/new.txt)); Files.createDirectories(Path.of(/tmp/a/b/c)); Files.deleteIfExists(path); // 读写 Files.writeString(path, hello); String content Files.readString(path); ListString lines Files.readAllLines(path); Files.write(path, List.of(line1, line2), StandardOpenOption.APPEND); // 复制、移动 Files.copy(src, dest, StandardCopyOption.REPLACE_EXISTING); Files.move(src, dest, StandardCopyOption.ATOMIC_MOVE); // 遍历目录 try (StreamPath stream Files.walk(Path.of(/tmp), 2)) { stream.filter(Files::isRegularFile) .forEach(System.out::println); } // 查找 try (StreamPath stream Files.find(Path.of(/tmp), Integer.MAX_VALUE, (p, attr) - p.toString().endsWith(.log))) { stream.forEach(System.out::println); }二、读取大文件java复制下载// 逐行读取内存友好 try (BufferedReader reader Files.newBufferedReader(path)) { String line; while ((line reader.readLine()) ! null) { process(line); } } // 流式读取 try (StreamString lines Files.lines(path)) { lines.filter(s - s.contains(ERROR)) .forEach(System.out::println); }三、内存映射文件MappedByteBuffer将文件映射到内存读写速度接近内存。java复制下载public class MappedFileReader { public static void main(String[] args) throws IOException { Path path Path.of(large.dat); try (FileChannel channel FileChannel.open(path, StandardOpenOption.READ)) { long size channel.size(); MappedByteBuffer buffer channel.map( FileChannel.MapMode.READ_ONLY, 0, size); byte[] data new byte[1024]; while (buffer.hasRemaining()) { int len Math.min(buffer.remaining(), data.length); buffer.get(data, 0, len); process(data, len); } } } }写入java复制下载try (FileChannel channel FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE)) { MappedByteBuffer buffer channel.map( FileChannel.MapMode.READ_WRITE, 0, 1024 * 1024); buffer.put(hello.getBytes()); buffer.force(); // 刷盘 }四、文件锁java复制下载try (FileChannel channel FileChannel.open(path, StandardOpenOption.WRITE)) { FileLock lock channel.tryLock(); if (lock ! null) { try { // 独占写 } finally { lock.release(); } } }五、WatchService监控目录java复制下载WatchService watchService FileSystems.getDefault().newWatchService(); Path dir Path.of(/tmp/watched); dir.register(watchService, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_DELETE); while (true) { WatchKey key watchService.take(); for (WatchEvent? event : key.pollEvents()) { System.out.println(event.kind() : event.context()); } key.reset(); }六、异步I/Ojava复制下载AsynchronousFileChannel channel AsynchronousFileChannel.open( path, StandardOpenOption.READ); ByteBuffer buffer ByteBuffer.allocate(1024); channel.read(buffer, 0, buffer, new CompletionHandlerInteger, ByteBuffer() { Override public void completed(Integer result, ByteBuffer attachment) { attachment.flip(); System.out.println(new String(attachment.array(), 0, result)); } Override public void failed(Throwable exc, ByteBuffer attachment) { exc.printStackTrace(); } });七、实战日志文件分析器java复制下载public class LogAnalyzer { public static MapString, Long countByLevel(Path logFile) throws IOException { try (StreamString lines Files.lines(logFile)) { return lines .filter(l - l.contains(ERROR) || l.contains(WARN) || l.contains(INFO)) .map(l - { if (l.contains(ERROR)) return ERROR; if (l.contains(WARN)) return WARN; return INFO; }) .collect(Collectors.groupingBy(s - s, Collectors.counting())); } } public static void main(String[] args) throws IOException { MapString, Long stats countByLevel(Path.of(app.log)); stats.forEach((k, v) - System.out.println(k : v)); } }八、总结NIO.2让文件操作更简洁。内存映射适合大文件随机访问WatchService适合目录监控异步I/O适合高并发场景。记住用try-with-resources管理资源。