JCR (Java Content Repository) is a java interface used to access contents that are not only web contents, but also other hierarchically stored data. The content is stored in a repository. The repository can be a file system, a relational database or an XML document. The internal structure of JCR data looks similar to an XML document, that means a document tree with nodes and data, but with a small difference, in JCR the data are stored in "property items".

Or better to cite the specification of JCR: "A content repository is a high-level information management system that is a superset of traditional data repositories."

How do you know the data of your website are stored? The images are probably in a file system, the meta data are in some dedicated files - maybe in XML - the text documents and pdfs are stored in different folders with the meta data in an other place (a database?) and in a proprietary structure. How do you manage to update these data and how do you manage the access rights? If your boss asks you to manage different versions of each document or not? The larger your website is, the more you need a Content Management Systems (CMS) which tackles all these issues.

These CMS solutions are sold by different vendors and each vendor provides its own API for interfacing the proprietary content repository. The developers have to deal with this and need to learn the vendor-specific API. If in the future you wish to switch to a different vendor, everything will be different and you will have a new implementation, a new interface, etc.

JCR provides a unique java interface for interacting with both text and binary data, for dealing with any kind and amount of meta data your documents might have. JCR supplies methods for storing, updating, deleting and retrieving your data, independent of the fact if this data is stored in a RDBMS, in a file system or as an XML document - you just don't need to care about. The JCR interface is also defined as classes and methods for searching, versioning, access control, locking, and observation.

Furthermore, an export and import functionality is specified so that a switch to a different vendor is always possible.

eXo fully complies a JCR standard JSR 170; therefore with eXo JCR you can use a vendor-independent API. It means that you could switch any time to a different vendor. Using the standard lowers your lifecycle cost and reduces your long term risk.

Of course eXo does not only offer JCR, but also the complete solution for ECM (Enterprise Content Management) and for WCM (Web Content Management).

In order to further understand the theory of JCR and the API, please refer to some external documents about this standard: