Java 檔案建立、寫入與刪除完整實作：從基本 IO 到 NIO.2 現代寫法

傳統 IO 實作（適用 Java 7 前環境）

public class FileUtil {
    private static final String BASE_PATH = "D:\\file\\";
    
    /** 建立檔案並寫入內容 */
    public static boolean createFile(String fileName, String content) {
        File file = new File(BASE_PATH + fileName + ".txt");
        try {
            if (!file.exists()) {
                file.createNewFile();
                return writeFileContent(file.getAbsolutePath(), content);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;
    }
    
    /** 追加寫入檔案內容 */
    public static boolean writeFileContent(String filePath, String newContent) {
        File file = new File(filePath);
        try (FileInputStream fis = new FileInputStream(file);
             InputStreamReader isr = new InputStreamReader(fis);
             BufferedReader br = new BufferedReader(isr);
             FileOutputStream fos = new FileOutputStream(file);
             PrintWriter pw = new PrintWriter(fos)) {
            
            StringBuilder buffer = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null) {
                buffer.append(line).append(System.lineSeparator());
            }
            buffer.append(newContent).append(System.lineSeparator());
            
            pw.write(buffer.toString().toCharArray());
            pw.flush();
            return true;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;
    }
    
    /** 刪除檔案 */
    public static boolean deleteFile(String fileName) {
        File file = new File(BASE_PATH + fileName + ".txt");
        return file.exists() && file.delete();
    }
}

現代 NIO.2 寫法（Java 7+ 推薦）

import java.nio.file.*;
import java.nio.charset.StandardCharsets;
import java.io.IOException;

public class ModernFileUtil {
    private static final Path BASE_DIR = Paths.get("D:/file");
    
    /** 原子性建立檔案並寫入（覆蓋模式） */
    public static void writeFile(String fileName, String content) throws IOException {
        Files.createDirectories(BASE_DIR);
        Path path = BASE_DIR.resolve(fileName + ".txt");
        Files.write(path, content.getBytes(StandardCharsets.UTF_8), 
            StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
    }
    
    /** 追加模式寫入 */
    public static void appendFile(String fileName, String content) throws IOException {
        Files.createDirectories(BASE_DIR);
        Path path = BASE_DIR.resolve(fileName + ".txt");
        Files.write(path, (content + System.lineSeparator()).getBytes(StandardCharsets.UTF_8),
            StandardOpenOption.CREATE, StandardOpenOption.APPEND);
    }
    
    /** 讀取全部內容 */
    public static String readFile(String fileName) throws IOException {
        Path path = BASE_DIR.resolve(fileName + ".txt");
        return Files.readString(path, StandardCharsets.UTF_8);
    }
    
    /** 刪除檔案（不存在不拋異常） */
    public static void deleteFile(String fileName) throws IOException {
        Path path = BASE_DIR.resolve(fileName + ".txt");
        Files.deleteIfExists(path);
    }
    
    /** 列出目錄下所有 .txt 檔案 */
    public static Stream listTxtFiles() throws IOException {
        return Files.list(BASE_DIR).filter(p -> p.toString().endsWith(".txt"));
    }
}

大檔案處理最佳實踐

• 分塊讀寫：使用 Files.newBufferedReader() / newBufferedWriter() 避免載入整個檔案到記憶體
• 緩衝區大小調優：預設 8KB，大檔案可調大至 64KB-256KB
• 非同步 IO：Java 7 AsynchronousFileChannel 配合 CompletionHandler 實現非阻塞操作
• 記憶體映射：FileChannel.map() 適合頻繁隨機存取的大檔案

編碼與跨平台注意事項

完整測試範例

public class FileDemo {
    public static void main(String[] args) {
        String uuid = UUID.randomUUID().toString();
        String content = "我的夢想不停留期待，就讓光線折射淚濕的瞳孔...";
        
        // 傳統 IO
        FileUtil.createFile(uuid + "_legacy", content);
        System.out.println("傳統 IO 讀取：" + FileUtil.readFile(uuid + "_legacy"));
        
        // NIO.2
        try {
            ModernFileUtil.writeFile(uuid + "_nio", content);
            System.out.println("NIO.2 讀取：" + ModernFileUtil.readFile(uuid + "_nio"));
            
            ModernFileUtil.appendFile(uuid + "_nio", "追加測試行");
            ModernFileUtil.listTxtFiles().forEach(System.out::println);
            
            ModernFileUtil.deleteFile(uuid + "_nio");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}