使用 Files 操作文件

查看

  1. Path path = Paths.get(System.getProperty("user.dir") 
  2.                       + "/jdk8Test/src/main/resources/file.txt");
  3. // 查看文件大小
  4. Files.size(path);

写入

  1. Path path = Paths.get(System.getProperty("user.dir") 
  2.                       + "/jdk8Test/src/main/resources/file.txt");
  4. // 写数据
  5. int writeCount = 100;
  6. List<String> info = IntStream.rangeClosed(0, writeCount)
  7.     .parallel()
  8.     .mapToObj(e -> "content" + e).collect(Collectors.toList());
  10. Files.write(path, info);

查询

  1.  int readCount = 20;
  2. // 2.1 读取
  3. List<String> collect = Files.lines(path).limit(readCount).collect(Collectors.toList());
  4. System.out.println(collect);
  6. // 2.2 跳过读取
  7. collect = Files.lines(path).skip(readCount).limit(readCount).collect(Collectors.toList());
  8. System.out.println(collect);
  10. // 3. 记录行数
  11. AtomicLong atomicLong = new AtomicLong(0L);
  12. Files.lines(path).forEach(e -> {
  13.     atomicLong.incrementAndGet();
  14. });
  15. System.out.println(atomicLong.get());

使用 Files 类静态方法进行文件操作注意释放文件句柄

  1. // 1 Too many open files
  2. // 并没有复现
  3. LongAdder longAdder = new LongAdder();
  4. LongAdder finalLongAdder = longAdder;
  5. IntStream.rangeClosed(1, 1000).forEach(i -> {
  6.     try {
  7.         Files.lines(path).forEach(line -> finalLongAdder.increment());
  8.     } catch (IOException e) {
  9.         e.printStackTrace();
  10.     }
  11. });
  13. // 2 用 try with resources 包裹
  14. longAdder = new LongAdder();
  15. LongAdder finalLongAdder1 = longAdder;
  16. IntStream.rangeClosed(1, 1000).forEach(i -> {
  17.     // try with resources
  18.     try (Stream<String> lines = Files.lines(path)) {
  19.         lines.forEach(line -> finalLongAdder1.increment());
  20.     } catch (IOException e) {
  21.         e.printStackTrace();
  22.     }
  23. });

复制

  • 使用 BufferedXXX 进行文件复制
  • 也可以使用 FileChannel ```java Path path = Paths.get(System.getProperty(“user.dir”) 
    1.                 + "/jdk8Test/src/main/resources/file.txt");
    Path pathTo = Paths.get(System.getProperty(“user.dir”)
    1.                   + "/jdk8Test/src/main/resources/file2.txt");

// 文件复制 FileChannel in = FileChannel.open(path); FileChannel out = FileChannel.open(pathTo, StandardOpenOption.CREATE, StandardOpenOption.WRITE); in.transferTo(0, in.size(), out); ```

BufferedXXX 的意义

  1. 内部维护一个 8kb 的缓冲区，应对不一样的场景
    1. 避免单字节读取的缓慢
    2. 避免应对未知大小数据时，如何取舍缓冲区的大小(反正就是用了就稳定有缓冲区了)