如何从字节数组中提取长数据类型？

Question

我需要制作一个字节数组，前八个字节应为当前时间戳，其余字节应保持原样。然后我想从同一个字节数组中提取我放在第一位的时间戳。

  public static void main(String[] args) {
    long ts = System.currentTimeMillis();
    byte[] payload = newPayload(ts);
    long timestamp = bytesToLong(payload);
    System.out.println(timestamp);
  }

  private static byte[] newPayload(long time) {
    ByteBuffer buffer = ByteBuffer.allocate(Long.SIZE / Byte.SIZE);
    byte[] payload = new byte[300];
    Arrays.fill(payload, (byte) 1);
    buffer.putLong(time);
    byte[] timeBytes = buffer.array();
    System.arraycopy(timeBytes, 0, payload, 0, timeBytes.length);
    return payload;
  }

  public static long bytesToLong(byte[] bytes) {
    byte[] newBytes = Arrays.copyOfRange(bytes, 0, (Long.SIZE / Byte.SIZE - 1));
    ByteBuffer buffer = ByteBuffer.allocate(Long.SIZE / Byte.SIZE);
    buffer.put(newBytes);
    buffer.flip();// need flip
    return buffer.getLong();
  }

上面的代码给了我异常，我不确定哪里出了问题？

Exception in thread "main" java.nio.BufferUnderflowException
    at java.nio.Buffer.nextGetIndex(Buffer.java:498)
    at java.nio.HeapByteBuffer.getLong(HeapByteBuffer.java:406)

Answer 1

来自 Arrays.copyOfRange 的文档：

to - the final index of the range to be copied, exclusive. (This index may lie outside the array.)

这意味着，您没有将足够的字节放入缓冲区。所以正确的做法是：

byte[] newBytes = Arrays.copyOfRange(bytes, 0, Long.SIZE / Byte.SIZE);

如何从字节数组中提取长数据类型？

How to extract long data type from the byte array?

java

arrays

byte

bytebuffer