将long转换为byte数组并将其添加到另一个数组

问题描述：

我想更改字节数组中的值以将长时间戳值放入MSB中。有人能告诉我什么是最好的方法。我不想逐位插入值，我认为这是非常低效的。

I want to change a values in byte array to put a long timestamp value in in the MSBs. Can someone tell me whats the best way to do it. I do not want to insert values bit-by-bit which I believe is very inefficient.

long time = System.currentTimeMillis();
Long timeStamp = new Long(time);
byte[] bArray = new byte[128];

我想要的是：

byte[0-63] = timeStamp.byteValue();

这样的事情是可能的。在此字节数组中编辑/插入值的最佳方法是什么。因为字节是原始的我不认为有一些我可以使用的直接实现？

Is something like this possible . What is the best way to edit/insert values in this byte array. since byte is a primitive I dont think there are some direct implementations I can make use of?

编辑：

似乎 System.currentTimeMillis（）比 Calendar.getTimeInMillis（）快，所以用它替换上面的代码。如果错误，请纠正我。

It seems that System.currentTimeMillis() is faster than Calendar.getTimeInMillis(), so replacing the above code by it.Please correct me if wrong.

答

有多种方法可以做到：

使用 ByteBuffer （最佳选择 - 简洁易读）：

Use a ByteBuffer (best option - concise and easy to read):

byte[] bytes = ByteBuffer.allocate(Long.SIZE / Byte.SIZE).putLong(someLong).array();

您还可以使用 DataOutputStream （更详细）：

You can also use DataOutputStream (more verbose):

ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
dos.writeLong(someLong);
dos.close();
byte[] longBytes = baos.toByteArray();

最后，您可以手动执行此操作（取自 LongSerializer 在Hector的代码中）（更难阅读）：

Finally, you can do this manually (taken from the LongSerializer in Hector's code) (harder to read):

byte[] b = new byte[8];
for (int i = 0; i < size; ++i) {
  b[i] = (byte) (l >> (size - i - 1 << 3));
}

然后你可以追加这些字节通过一个简单的循环到你现有的数组：

Then you can append these bytes to your existing array by a simple loop:

// change this, if you want your long to start from 
// a different position in the array
int start = 0; 
for (int i = 0; i < longBytes.length; i ++) {
   bytes[start + i] = longBytes[i];
}

将long转换为byte数组并将其添加到另一个数组

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