Transforming a Java UUID object to a .NET GUID string

Question

In a Java method that receives a java.util.UUID Object, I would like to display this object as a string in the .NET/C# format (CSUUID).

Currently I am only able to display it in the Java format (JUUID) :

static String GetStringFromUuid (java.util.UUID myUuid){
    return myUuid.toString();
}

Current output: "46c7220b-1f25-0118-f013-03bd2c22d6b8"

Desired output: "1f250118-220b-46c7-b8d6-222cbd0313f0"

Context:

The UUID is stored in MongoDB and is retrieved with the Java ETL program Talend (tMongoDBInput component).
In the Java program, the method already receives the UUID as a java.util.UUID Object (I do not have directly access to the BinData in the program).
I need to display the UUID in the C# format since other programs already display the UUIDs with the C# format.
In case it might be useful, the example data is stored in MongoDB like this: BinData(3,"GAElHwsix0a41iIsvQMT8A==")
I need a solution in Java.

Can you clarify the difference between your two (aside from them being different guid)? — theMayer
– theMayer, Commented Mar 5, 2018 at 2:15
A guid is simply a 128-Bit number. There are a few different ways to write it, but the format you put is most common (uses only 0-9 a-f) — theMayer
– theMayer, Commented Mar 5, 2018 at 2:16
@theMayer as explained in Evk's answer, the bytes are not printed in the same order in Java vs .NET — YABADABADOU
– YABADABADOU, Commented Mar 5, 2018 at 14:22
OK, I didn't understand that this was the same guid output using two different platforms. I'm glad someone figured this out, but the question could have been written more clearly. — theMayer
– theMayer, Commented Mar 5, 2018 at 18:03

Evk · Accepted Answer · 2018-03-05 06:39:47Z

6

+250

Guid is represented by 16 bytes. For various reasons, both Java and .NET do not just print those bytes in order when you call toString. For example, if we look at base-64 encoded guid from your question:

GAElHwsix0a41iIsvQMT8A==

In hex form it will look like this:

18-01-25-1f-0b-22-c7-46-b8-d6-22-2c-bd-03-13-f0

Java toString produces this (if we format as above):

46-c7-22-0b-1f-25-01-18-f0-13-03-bd-2c-22-d6-b8

.NET ToString produces this:

1f-25-01-18-22-0b-46-c7-b8-d6-22-2c-bd-03-13-f0

If you look at this for some time - you will notice that both java and .NET strings represent the same 16 bytes, but positions of those bytes in output string are different. So to convert from java representation to .NET you just need to reorder them. Sample code (I don't know java, so probably it could be done in a better way, but still should achieve the desired result):

static String GetStringFromUuid (java.util.UUID myUuid){
    byte[] bytes = new byte[16];
    // convert uuid to byte array
    ByteBuffer bb = ByteBuffer.wrap(bytes);
    bb.putLong(myUuid.getMostSignificantBits());
    bb.putLong(myUuid.getLeastSignificantBits());
    // reorder
    return String.format("%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
        bytes[4],bytes[5],bytes[6],bytes[7],
        bytes[2],bytes[3],bytes[0],bytes[1],
        bytes[15],bytes[14],bytes[13],bytes[12],
        bytes[11],bytes[10],bytes[9],bytes[8]);
}

answered Mar 5, 2018 at 6:39

Evk

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1 Comment

YABADABADOU Over a year ago

I tested the solution and I confirm that it works! Thank you so much for your help!

Nishanth · Accepted Answer · 2018-03-03 21:50:55Z

1

We can just keep the GUID as string, if the c# function is receiving the string and it needs to be displayed or sent to some service as string

Just in case if you want to parse it. You can use the link for GUID parsing logic example

For creating new GUID in C#, use

var guid = System.Guid.NewGuid();
var guidString = guid.ToString();

For creating new UUID in Java, use

UUID uuid = java.util.UUID.randomUUID();
String uuidString = uuid.toString();

edited Mar 3, 2018 at 21:50

answered Mar 3, 2018 at 0:44

Nishanth

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4 Comments

YABADABADOU Over a year ago

Thanks for your answer. I don't know right now how to get the GUID string (C# implementation of UUID). I only have a Java UUID object and it's not useful for me to store the JUUID string. The C# function is not receiving the string.

Nishanth Over a year ago

if you want to create new GUID in C#, use following code System.Guid.NewGuid().ToString()

YABADABADOU Over a year ago

I think this is a C# method. Unfortunately I need something in Java.

Nishanth Over a year ago

In Java you need to use java.util.UUID.randomUUID()

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