如何将 Java Long 转换为 Cassandra 的 byte[]？
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How to convert a Java Long to byte[] for Cassandra?
提问by dfrankow
Lazy programmer alert. :)
懒惰的程序员警报。:)
Cassandra stores column values as bytes (Java example). Specifying a LongType comparatorcompares those bytes as a long. I want the value of a long into a Cassandra-friendly byte[]. How? I poked around for awhile. I think you people can help me faster.
Cassandra 将列值存储为字节（Java 示例）。指定LongType 比较器会将这些字节作为 long 进行比较。我希望将 long 的值转换为对 Cassandra 友好的 byte[]。如何？我摸索了一会儿。我认为你们可以更快地帮助我。
EDIT:
编辑：
Both Alexander and Eli's answers agreed with this reverse transformation. Thanks!
Alexander 和 Eli 的回答都同意这种逆向转换。谢谢！
采纳答案by Alexander Pogrebnyak
Here is cut and paste from java 6 DataOutputStream.writeLong
这是从 java 6 剪切和粘贴 DataOutputStream.writeLong
public final void writeLong(long v) throws IOException {
writeBuffer[0] = (byte)(v >>> 56);
writeBuffer[1] = (byte)(v >>> 48);
writeBuffer[2] = (byte)(v >>> 40);
writeBuffer[3] = (byte)(v >>> 32);
writeBuffer[4] = (byte)(v >>> 24);
writeBuffer[5] = (byte)(v >>> 16);
writeBuffer[6] = (byte)(v >>> 8);
writeBuffer[7] = (byte)(v >>> 0);
out.write(writeBuffer, 0, 8);
incCount(8);
}
Here are modifications for your case
以下是针对您的案例的修改
public final byte[] longToBytes(long v) {
byte[] writeBuffer = new byte[ 8 ];
writeBuffer[0] = (byte)(v >>> 56);
writeBuffer[1] = (byte)(v >>> 48);
writeBuffer[2] = (byte)(v >>> 40);
writeBuffer[3] = (byte)(v >>> 32);
writeBuffer[4] = (byte)(v >>> 24);
writeBuffer[5] = (byte)(v >>> 16);
writeBuffer[6] = (byte)(v >>> 8);
writeBuffer[7] = (byte)(v >>> 0);
return writeBuffer;
}
回答by Eli Courtwright
I would write the long to a ByteArrayOutputStreamwrapped in a DataOutputStreamand then retrieve the raw bytes, although this will always give you your data in big endian byte order (most significant byte first):
我会将 long 写入包装在DataOutputStream 中的ByteArrayOutputStream，然后检索原始字节，尽管这将始终以大端字节顺序（最重要的字节在前）为您提供数据：
public static byte[] getBytes(Long val)
throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
dos.writeLong(val);
return baos.toByteArray();
}
If you want to be able to specify the endianness, you can use the ByteBufferclass:
如果您希望能够指定字节顺序，可以使用ByteBuffer类：
public static byte[] getBytes(Long val)
{
ByteBuffer buf = ByteBuffer.allocate(8);
buf.order(ByteOrder.BIG_ENDIAN);
buf.putLong(val);
return buf.array();
}
回答by Michal
You can use Cassandra's utility class: ByteBufferUtil.bytes(long n)
您可以使用 Cassandra 的实用程序类： ByteBufferUtil.bytes(long n)
回答by President James K. Polk
You can crack the bytes apart by using shifts and mask, or a bit easier is ByteBuffer.wrapto wrap an 8 long byte array and using the putLongmethod. You must set the ByteOrder first using the ByteBuffer.ordermethod.
您可以通过使用移位和掩码来分解字节，或者更容易一点的是ByteBuffer.wrap包装一个 8 长字节数组并使用该putLong方法。您必须首先使用该ByteBuffer.order方法设置 ByteOrder 。
