Question

我尝试使用nio读取仅包含5个字符的小文本，但是fileChannel.read循环永远不会结束。

public static void main(String[] args) throws IOException {
        FileChannel fileChannel = FileChannel.open(Paths.get("input.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE);
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        while (fileChannel.read(byteBuffer) != -1) {
            byteBuffer.flip();
            while (byteBuffer.hasRemaining()) {
                char c = (char)byteBuffer.get();
                System.out.println(c);
            }
        }
    }

Answer 1

问题是您忘记在内部while循环之后重置缓冲区的限制和位置。读取第一个1024个字符后，缓冲区将已满，并且每次尝试读入缓冲区的尝试都会尝试读取remaining = limit - position字节，即缓冲区已满时为0字节。

此外，您应该始终捕获fileChannel.read()的返回值。就您而言，它会告诉您它不断返回0。

在内循环之后调用byteBuffer.clear()解决了该问题：

public static void main(String[] args) throws IOException {
  FileChannel fileChannel = FileChannel.open(Paths.get("JPPFConfiguration.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE);
  ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
  int n;
  long sum = 0L;
  while ((n = fileChannel.read(byteBuffer)) != -1) {
    sum += n;
    byteBuffer.flip();
    while (byteBuffer.hasRemaining()) {
      char c = (char) byteBuffer.get();
      System.out.print(c);
    }
    System.out.println("\n read " + n  + " bytes");
    byteBuffer.clear();
  }
  System.out.println("read " + sum + " bytes total");
}

为什么fileChannel.read循环永远不会结束？

1 个答案: