Android: Create unique string for file name

Question

I'm doing an android application for image viewer. This app will download the image, and store them in a cache folder.

So, in the cache folder, the image file name must be unique. Currently, I use String.hashCode() to generate the file name.

Are there any other better ways to get unique string?

ChrisJ · Accepted Answer · 2011-02-26 11:23:47Z

24

Use java.util.UUID. Look at randomUUID that generates a so-called Universally unique identifier.

I don't really understand how you intend to generate a “unique” value with String.hashCode. On what string do you call hashCode? hashCode's purpose is not to generate unique IDs... It's meant to generate a hash code for a string, so if the strings themselves are not unique, the hash codes won't be either.

answered Feb 26, 2011 at 11:23

ChrisJ

5,28127 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

James Over a year ago

Thank you for answer it. Actually, what i did is to store the online image to the local. Because each image has unique url, I use url.hashcode to generate the file name. I just wonder if there will be a performance issue to use hashcode to do it. So I want to know the common way how you save the cache file, and make them unique.

Sileria Over a year ago

That is the whole purpose, to be able to get a unique and specific ID for a specific url. If you create random UUID then you will have to maintain a map of urls and IDs. But hashcode will always return the same id for a particular id.

Tigran Sarkisian Over a year ago

String uuid = UUID.randomUUID().toString().replaceAll("-", "");

Yuliia Ashomok · Accepted Answer · 2019-05-01 10:21:48Z

23

Use java.util.UUID.

  String uniqueString = UUID.randomUUID().toString();

edited May 1, 2019 at 10:21

answered Mar 16, 2018 at 18:00

Yuliia Ashomok

8,6482 gold badges63 silver badges74 bronze badges

Comments

guido · Accepted Answer · 2011-02-26 11:42:48Z

3

ChrisJ suggestion to use UUID.randomUUID() is a good alternative; but i'd prefer to have the cache backed up by a database table:

ID (PK) | original filename | original URL

and then using the primary key as filename in cache dir.

If you plan to have lots of files, having a directory tree structure like:

0 
+--- 0
     +---- 01.jpg
     +---- 02.jpg
     +---- ...
     +---- 0f.jpg
+--- 1
     +---- 10.jpg
     +---- ...
     +---- cc.jpg

after converting the primary key to hex could also be a cleaner solution, but you will have to decide a left padding for the filenames, which will be a function of the directory tree depth and the number of files per leaf directory.

answered Feb 26, 2011 at 11:42

guido

19.3k6 gold badges74 silver badges97 bronze badges

1 Comment

James Over a year ago

It's implementable. But I already has caching them in different way. And I only cache the file after it was stored in local completely.

Collectives™ on Stack Overflow

Android: Create unique string for file name

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related