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https://issues.apache.org/jira/browse/JCR-5140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17945443#comment-17945443
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Julian Reschke commented on JCR-5140:
-------------------------------------
Example use case in Oak:
https://github.com/apache/jackrabbit-oak/blob/34e7fd65b2815b3c4944fe4dc96032dedadb65a3/oak-jcr/src/main/java/org/apache/jackrabbit/oak/jcr/session/SessionNamespaces.java#L165
> Improve support for generating namespace prefixes
> -------------------------------------------------
>
> Key: JCR-5140
> URL: https://issues.apache.org/jira/browse/JCR-5140
> Project: Jackrabbit Content Repository
> Issue Type: Task
> Components: jackrabbit-jcr-commons
> Reporter: Julian Reschke
> Assignee: Julian Reschke
> Priority: Major
>
> There are a few use cases where a new namespace prefix needs to be computed
> for a given namespace name (this list may not be exhaustive):
> - when mapping expanded names to JCR names when the namespace name (URI) is
> not known in the repository (yet)
> - when importing content where namespace names (URIs) are known, but
> prefixes may be not
> - when registering a new namespace, but the specified prefix is already in
> use
> Automatically generating the prefixes has several commons problems:
> - consistency: generating prefixes in different places and/or based on
> previous state of the registry (such as by incrementing counters until new
> non-conflicting prefix found) causes prefix inconsistency across systems for
> no good reason
> - conciseness and readability: for certain namespaces, there are commonly
> used prefixes (such as in DC, XMPP etc), and it would be good to just use
> those when possible
> Proposal: have a single place that offers help for generating prefixes (this
> ticket is in JCR space as jackrabbit-jcr-commons already has NamespaceHelper,
> but of course the location can be discussed). We may want to start in
> oak-commons, so that we can more quickly iterate in Oak, and then maybe later
> move this into JCR commons.
> Blue print:
> {code:java}
> // Suggests a prefix for the given namespace, based on
> // well-known XML namespaces, or alternatively derived
> // from the namespace name.
> public static String suggestPrefix(String namespace);
> // as above, but will take exisiting prefixes into account
> // this would be for the case where the prefix already exists
> // but is mapped to a different namespace name.
> // Lookup for existing prefix so that we can abstract out the
> // actual JCR interface (to be discussed)
> public static String suggestPrefix(String namespace, Function<String, String>
> getNamespaceForPrefix);
> // maybe more helpers:
> public static boolean isValidNamespace(String namespace);
> public static Map.Entry<String, String> extractPrefixAndNamespace(String
> jcrName, Function<String, String> getNamespaceForPrefix);{code}
> We'd also need a hook to account for "internal", unless we want to hard-wire
> that into this.
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