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From conflue...@apache.org
Subject [CONF] Apache Jackrabbit: Frequently Asked Questions (page edited)
Date Thu, 02 Apr 2009 10:31:00 GMT
Frequently Asked Questions (JCR) edited by Thomas Mueller
      Page: http://cwiki.apache.org/confluence/display/JCR/Frequently+Asked+Questions
   Changes: http://cwiki.apache.org/confluence/pages/diffpagesbyversion.action?pageId=75346&originalVersion=7&revisedVersion=8


h2. General

h3. What is JCR?

JCR is the acronym of the Content Repository for Java technology API, a standard interface
for accessing content repositories. JCR version 1.0 was specified in Java Specification Request
170 ([JSR 170|http://jcp.org/en/jsr/detail?id=170]), and version 2.0 is currently under work
in [JSR 283|http://jcp.org/en/jsr/detail?id=283].

h3. What is a content repository?

A content repository is an information management system that provides various services for
storing, accessing, and managing content. In addition to a hierarchically structured storage,
common services of a content repository are versioning, access control, full text searching,
and event monitoring. A content repository is not a content management system (CMS), although
most existing CMSs contain a custom content repository implementation, often based on the
file system or a relational database.

h3. What is Apache Jackrabbit?

Apache Jackrabbit is a fully featured content repository that implements the entire JCR API.
 The Jackrabbit project was started when Day Software, the JSR-170 specification lead, licensed
their initial implementation of the JCR reference implementation. The Jackrabbit codebase
was used for the official reference implementation (RI) and technology compatibility kit (TCK)
released along with the final JCR API.

h3. What do I do if I have a question?

Please ask questions on the [Jackrabbit mailing lists|http://incubator.apache.org/jackrabbit/mail-lists.html
]. There is the users list for questions around using JCR and Jackrabbit and the dev list
for the development of Jackrabbit itself and for people starting to extend Jackrabbit or other
advanced topics.

h2. Building Jackrabbit

h3. How do I build the Apache Jackrabbit sources?

See the [Building Jackrabbit] page for detailed build instructions.

h2. Using Jackrabbit

h3. How do I do X with JCR/Jackrabbit?

See the JCR specification, the JCR API documentation, or the Examples page on the Jackrabbit
wiki for information on how to perform various operation using the JCR API.

For Jackrabbit features (like access control and node type management) not covered by the
JCR API, see the Examples page on the wiki, the Jackrabbit javadocs, or contact the Jackrabbit
mailing list.

h3. How do I use transactions with JCR?

See the mailing list announcement for a simple example on using the JTA support in Jackrabbit.
For a more complete explanation of the transaction features, please           see section
8.1 Transactions of the JCR specification.

h3. How do I create new workspaces in Jackrabbit?

The JCR API does not contain features for creating or managing workspaces, so you need to
use Jackrabbit-specific functionality for creating new workspaces. You can create a new workspace
either manually or programmatically.

The manual way is to create a new workspace directory within the repository home directory
and to place a new workspace.xml configuration file in that folder. You can use the configuration
file of an existing workspace as an example, just remember to change the name of the workspace
          in the Workspace name="..." tag. See the [Jackrabbit Configuration] page for configuration
details. Note also that you need to restart the repository instance to access the new workspace.

The programmatic way is to acquire a Workspace instance using the normal JCR API and to cast
the instance to the JackrabbitWorkspace interface. You can then use the createWorkspace(String)
method to create new workspaces.

h3. How do I delete a workspace in Jackrabbit?

There is currently no programmatic way to delete workspaces. You can delete a workspace by
manually removing the workspace directory when the repository instance is not running.

h3. How do I deploy Jackrabbit into Tomcat?

* Download [jcr-1.0.jar|http://www.day.com/maven/javax.jcr/jars/jcr-1.0.jar] and put it into
* Get the WAR distribution from the [Downloads] page and deploy it into Tomcat.
* Point your browser to {{http://}}{{localhost:8080/jackrabbit-webapp-<version>/}}

h2. Access control

h3. How do I use LDAP, Kerberos, or some other authentication mechanism         with Jackrabbit?

Jackrabbit uses the Java Authentication and Authorization Service (JAAS) for authenticating
users. You should be able to use any           JAAS LoginModule implementation (e.g. the LoginModules
in thecom.sum.security.auth.modulepackage) for authentication. See the JAAS documentation
for           configuration instructions.

h3. How do I manage the access rights of authenticated users?

The current JackrabbitSimpleAccessManager class only supports three access levels: anonymous,
normal, and           system. Anonymous users have read access while normal and system   
       users have full read-write access. You need to implement a custom AccessManager class
to get more fine-grained access control.

h2. Persistence managers

h3. What is a persistence manager?

A persistence manager (PM) is an internal Jackrabbit           component that handles the
persistent storage of content nodes           and properties. Each workspace of a Jackrabbit
content repository           uses a separate persistence manager to store the content in that
          workspace. Also the Jackrabbit version handler uses a separate           persistence
manager.The persistence manager sits at the very bottom layer of the           Jackrabbit
system architecture. Reliability, integrity and           performance of the PM are crucial
to the overall           stability and performance of the repository. If e.g. the data   
       that a PM is based upon is allowed to change through external           means the integrity
of the repository would be at risk           (think of referential integrity / node references

In practice, a persistence manager is any Java class that           implements the PersistenceManager
           interface and the associated behavoural contracts. Jackrabbit           contains
a set of built-in persistence manager classes that cover           most of the deployment
needs. There are also a few contributed           persistence managers that give additional

h3. What is a Jackrabbit file system?

A Jackrabbbit file system (FS) is an internal component that           implements standard
file system operations on top of some underlying           storage mechanism (a normal file
system, a database, a webdav server,           or a custom file format). A file system component
is any Java class           that implements the FileSystem            interface and the associated
behavioral contracts. File systems           are used in Jackrabbit both as subcomponents
of the persistence           managers and for general storage needs (for example to store
the           full text indexes).

h3. Can I use a persistence manager to access an existing data source?

No. The persistence manager interface was never intended as being           a general SPI
that you could implement in order to integrate           external data sources with proprietary
formats (e.g. a customers           database). The reason why we abstracted the PM interface
was           to leave room for future performance optimizations that would           not
affect the rest of the implementation (e.g. by storing the           raw data in a b-tree
based database instead of individual file).

h3. How smart should a persistence manager be?

A persistence manager should not be intelligent, i.e.           it should not interpret the
content it is managing.           The only thing it should care about is to efficiently, 
         consistently, and reliably store and read the content encapsulated           in the
passed NodeState and PropertyState objects. Though it           might be feasible to write
a custom persistence manager to           represent existing legacy data in a level-1 (read-only)
repository,           I don't think the same is possible for a level-2 repository and    
      I certainly would not recommend it.

h2. Query

h3. I've configured textFilterClasses but my query still doesn't work, what's wrong?

Make sure you changed existing workspace.xml files as well. The workspace element in repository.xml
only acts as a template for new workspaces.

Verify that you also put the jar files into the classpath that jackrabbit depends on for text
extraction. You can find all required jar files inside the jackrabbit-webapp war file (the
{{WEB-INF/lib}} folder). Go to the [downloads|Downloads] page to get the war file.

Some documents may still not be searchable for various reasons: the document is corrupt, bug
in one of the libraries that extract text, document is encrypted or otherwise protected, etc.

h3. Why doesn't {{//*\[jcr:contains(@jcr:data, 'foo')]}} return matches for binary content?

Extracted text from binary content is only indexed on the parent node of the @jcr:data property.
Use jcr:contains() on the nt:resource node.
//element(*, nt:resource)[jcr:contains(., 'foo')] 
//element(*, nt:file)[jcr:contains(jcr:content, 'foo')] 

h3. Can I use the Lucene field syntax in jcr:contains()?

No, you cannot. Even though Jackrabbit uses a Lucene index, the fields for JCR properties
do not map 1:1 to Lucene fields. Instead you can use the following:

//element(*, book)[jcr:contains(@title, 'jackrabbit') and jcr:contains(@text, 'query')]

h3. My XPath query returns no results when I add a path constraint, what's wrong?

You probably forgot to prefix your statement with {{/jcr:root}}.

JSR 170 says in section
The context node of an XPath query is the XML node relative to which the query expression
is evaluated.

A relative XPath statement (one that does not have a leading /) will be interpreted relative
to the root node of the workspace, which, in the XML document view is the top-most XML element,
<jcr:root>. This means that one should not include jcr:root as the first segment in
a relative XPath statement, since that element is already the default context node.

An absolute XPath (one with a leading /), in contrast, will be interpreted relative to a position
one level above <jcr:root>. This means that an absolute XPath must either begin with
// or with /jcr:root in order to match anything at all.

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