问题描述

如何将 long 转换为 byte[] 并返回 Java?

How do I convert a long to a byte[] and back in Java?

我正在尝试将 long 转换为 byte[] 以便能够通过TCP 连接.另一方面，我想把那个 byte[] 转换回 double.

I'm trying convert a long to a byte[] so that I will be able to send the byte[] over a TCP connection. On the other side I want to take that byte[] and convert it back into a double.

推荐答案

public byte[] longToBytes(long x) {
    ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);
    buffer.putLong(x);
    return buffer.array();
}

public long bytesToLong(byte[] bytes) {
    ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);
    buffer.put(bytes);
    buffer.flip();//need flip 
    return buffer.getLong();
}

或者封装在一个类中以避免重复创建ByteBuffers:

Or wrapped in a class to avoid repeatedly creating ByteBuffers:

public class ByteUtils {
    private static ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);    

    public static byte[] longToBytes(long x) {
        buffer.putLong(0, x);
        return buffer.array();
    }

    public static long bytesToLong(byte[] bytes) {
        buffer.put(bytes, 0, bytes.length);
        buffer.flip();//need flip 
        return buffer.getLong();
    }
}

<小时>

由于它变得如此流行，我只想提一下，我认为在绝大多数情况下使用像 Guava 这样的库会更好.如果您对库有一些奇怪的反对意见，您可能应该首先考虑 this answer 对于原生 java 解决方案.我认为我的回答真正要解决的主要问题是您不必自己担心系统的字节序.

Since this is getting so popular, I just want to mention that I think you're better off using a library like Guava in the vast majority of cases. And if you have some strange opposition to libraries, you should probably consider this answer first for native java solutions. I think the main thing my answer really has going for it is that you don't have to worry about the endian-ness of the system yourself.

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