CODEWITHSUNDEEP
javahashfilenames
DCKing
DCKing

Reputation: 4273

File name compatible hash values in Java

To generate some uniqueness in file system names of user-provided files, I generate a hash value of some other user-supplied data (in this case the user's IP address and a random integer) and prefix the filename with it. I chose the SHA-1 algorithm to perform this hash. Unfortunately, the String returned from

md = MessageDigest.getInstance("SHA-1");
// Add values to the digest
String ipAddrHash = new String(md.digest());

...of course contains all sorts of weird exotic characters, most of which are not allowed in file names.

So, either:

Upvotes: 0

Views: 2645

Answers (4)

tomi
tomi

Reputation: 716

You can encode returned String with Base32 or Base64 with replacing "/" character with safe one (for example: "_").

Upvotes: 0

jzafrilla
jzafrilla

Reputation: 1436

Try:

String filename=UUID.randomUUID().toString()

Upvotes: 2

hmjd
hmjd

Reputation: 121961

If it is only uniqueness use a java.util.UUID. FWIW, I had a similar requirement and this is what I used to solve it (software operating on both linux and windows). A UUID contains alphanumerics and hyphens only so no issues with incompatible file system characters and guarantees uniqueness.

Upvotes: 1

JB Nizet
JB Nizet

Reputation: 691625

You could encode the bytes in hexadecimal to get a printable file name. But your algorithm doesn't guarantee uniqueness.

Or you could simply use a UUID, or a sequence number returned from a database sequence.

Upvotes: 3

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