How to read a .NET Guid into a Java UUID
Could you not just store the .Net Guid as a string and read it into Java? That way you don't need to worry about byte order or anything.
If not then This explains how the bytes are laid out in C#
http://msdn.microsoft.com/en-us/library/fx22893a.aspx
Edit 2017-08-30: Swapped array elements 6 and 7 per comments.
I have to read & write Guids from/to MySQL (stored as binary(16)) in a C# app, but the database is also used by Java apps. Here are the extension methods I use for converting between .NET little-endian and Java big-endian byte order:
public static class GuidExtensions
{
/// <summary>
/// A CLSCompliant method to convert a Java big-endian Guid to a .NET
/// little-endian Guid.
/// The Guid Constructor (UInt32, UInt16, UInt16, Byte, Byte, Byte, Byte,
/// Byte, Byte, Byte, Byte) is not CLSCompliant.
/// </summary>
[CLSCompliant(true)]
public static Guid ToLittleEndian(this Guid javaGuid) {
byte[] net = new byte[16];
byte[] java = javaGuid.ToByteArray();
for (int i = 8; i < 16; i++) {
net[i] = java[i];
}
net[3] = java[0];
net[2] = java[1];
net[1] = java[2];
net[0] = java[3];
net[5] = java[4];
net[4] = java[5];
net[6] = java[7];
net[7] = java[6];
return new Guid(net);
}
/// <summary>
/// Converts little-endian .NET guids to big-endian Java guids:
/// </summary>
[CLSCompliant(true)]
public static Guid ToBigEndian(this Guid netGuid) {
byte[] java = new byte[16];
byte[] net = netGuid.ToByteArray();
for (int i = 8; i < 16; i++) {
java[i] = net[i];
}
java[0] = net[3];
java[1] = net[2];
java[2] = net[1];
java[3] = net[0];
java[4] = net[5];
java[5] = net[4];
java[6] = net[7];
java[7] = net[6];
return new Guid(java);
}
}
As already noted, the binary encoding of GUID in .NET has bytes in the first three groups placed in the little-endian order (reversed) – see Guid.ToByteArray Method. To create java.util.UUID
from it you can use the following code:
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.UUID;
public UUID toUUID(byte[] binaryEncoding) {
ByteBuffer source = ByteBuffer.wrap(binaryEncoding);
ByteBuffer target = ByteBuffer.allocate(16).
order(ByteOrder.LITTLE_ENDIAN).
putInt(source.getInt()).
putShort(source.getShort()).
putShort(source.getShort()).
order(ByteOrder.BIG_ENDIAN).
putLong(source.getLong());
target.rewind();
return new UUID(target.getLong(), target.getLong());
}