This document discusses Universally Unique Identifiers (UUIDs). It begins with an introduction to UUIDs and their uses. It then describes the five versions of UUID and how to generate them in Java. Specifically, it explains that Java can generate version 3 UUIDs using name and MD5 hash, and version 4 UUIDs randomly. It also provides steps to generate version 1 UUIDs in Java and Android by using a third-party library and removing unsupported CORBA APIs. The document concludes with references to RFC 4122 and Wikipedia for more information on UUID standards and properties.

1. UUID
Tomoki Yamashita
2014.4.9 potatotips #6

2. Self-Introduction
• @tomorrowkey / Tomoki Yamashita
• Android Developer at COOKPAD
• http://blog.tomorrowkey.jp / 明日の

3. Agenda
• What is UUID?
• How to use it in Java
• Versions of UUID
• Which version can we use in Java
• To use version 1 in Java
• To use version 1 in Android

4. What is UUID

5. What is UUID?
• Universally Unique Identifier
• RFC 4122
• Generate Unique ID without servers.

6. How to use in
Java

7. How to use it in Java
import java.util.UUID;
public class Main {
public static void main(String... args) {
UUID uuid = UUID.randomUUID();
System.out.println(“uuid=” + uuid.toString());
}
}
#
53da3b97-075f-4bcd-af62-148b1a7d6712

8. Versions of UUID

9. Versions of UUID
• There are 5 versions of UUID.

10. Version 1
• Original version
• Use time(nano-seconds) and Mac
Address
• It won't duplicate because depends on
mac address.

11. Version 2
• Version for DCE(Distributed
Computing Environment) Security

12. Version 3
• Name and MD5 Hash
• If use the same name, it duplicate.

13. Version 4
• Random value
• It may not duplicate.

14. Version 5
• Name and SHA1 Hash
• If use the same name, it duplicate.

15. Which version can
we use in Java?

16. Which version can we
use in Java?
• Version 3
UUID.nameUUIDFromBytes(byte[] name)
• Version 4
UUID.randomUUID();

17. To use version1
in Java

18. To use version1
in Java
stephenc/eaio-uuid
https://github.com/stephenc/eaio-uuid

19. To use version1
in Java
build.gradle
compile ‘com.github.stephenc.eaio-uuid:uuid:3.4.0'
Main.java
com.eaio.uuid.UUID uuid = new com.eaio.uuid.UUID();
System.out.println(“uuid=” + uuid.toString());

20. To use version1
in Android

21. To use version1
in Android
build.gradle
compile ‘com.github.stephenc.eaio-uuid:uuid:3.4.0'
Main.java
com.eaio.uuid.UUID uuid = new com.eaio.uuid.UUID();
System.out.println(“uuid=” + uuid.toString());

22. To use version1
in Android
build.gradle
compile ‘com.github.stephenc.eaio-uuid:uuid:3.4.0'
Main.java
com.eaio.uuid.UUID uuid = new com.eaio.uuid.UUID();
System.out.println(“uuid=” + uuid.toString());
NoClassDefFoundError: com.eaio.uuid.UUID

23. Why...?
The library use a api which is not
supported in Android.
omg.CORBA.portable.IDLEntity

24. To use version1
in Android
• clone eaio-uuid
• remove CORBA api from source code.
• add a permission INTERNET

25. End
Understand principle about UUID and
then use it.
Thank you for listening

26. Referred links
RFC 4122 - A Universally Unique IDentifier (UUID) URN Namespace
http://tools.ietf.org/html/rfc4122
Universally unique identifier - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/UUID#Variants_and_versions
UUIDはなぜ、分散環境で好き勝手に生成しても衝突しないのか。RFC4122規格とUUIDの性質。 ¦ 三
度の飯とエレクトロン
http://blog.katty.in/5124