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From Jukka Zitting <jukka.zitt...@gmail.com>
Subject Re: JR Future idea
Date Wed, 21 Mar 2012 10:00:17 GMT
Hi Francisco,

On Tue, Mar 20, 2012 at 9:59 PM, Francisco Carriedo Scher
<fcarriedos@gmail.com> wrote:
> I can imagine lots of questions to properly integrate this (efficient
> methods for asking about the existence, for instance), but i really need
> some (expertise) tips to do this... Let's say, an entry point...

For now one of the main goals of the data store design was to avoid
duplicating binaries that already exist in the repository, for example
when copying or versioning existing content. We didn't put much effort
into thinking how an external client could also leverage this feature
like you're suggesting. But I agree that it's a good use case, so
thanks for following up on this!

As for how to implement this on top of the JCR API, the main thing
you'd need is a Value reference that matches a given content hash. To
start with this identifier was completely internal, but in JCR-1892
[1] we already started exposing it through the
JackrabbitValue.getContentIdentity() [2] extension. What you'd need
then is another extension method, for example
JackrabbitValueFactory.createBinary(String) or something similar, that
turns a given content hash to a matching binary Value (or returns null
if a matching value is not found).

With such a method, your client could work roughly like this:

    File file = ...;
    String hash = computeContentHash(file);

    // Check if the binary already exists in the repository
    JackrabbitValueFactory factory = ...;
    Binary binary = factory.createBinary(hash);
    if (binary == null) {
        // Doesn't exist yet, so stream it to the repository
        binary = factory.creatBinary(new FileInputStream(file));
    }

    Node node = ...;
    node.setProperty(Property.JCR_DATA, binary);

Does this help you forward?

[1] https://issues.apache.org/jira/browse/JCR-1892
[2] http://jackrabbit.apache.org/api/2.4/org/apache/jackrabbit/api/JackrabbitValue.html#getContentIdentity()

BR,

Jukka Zitting

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