Up to and including v2.4, Sakai used a Content Hosting Service that stored its content in a DB and on the file system. In 2.5 storage in a Java Content Repository was also enabled, by the addition of the 'Content Hosting Service with JCR Storage'. In addition, 'JCRService' (a minimal shim on JCR) gave direct access to the JCR, but did not implement the whole of legacy Content Hosting Service. Finally, a 'Content Hosting Service Multiplexer' and 'Content Migration Service' were provided to ease migration of data from legacy CHS DB and Filestore storage to JCR storage. Legacy code is shown in blue and 2.5 release additions are shown in green in the diagram below.
The services above were created on the assumption that new tools would be written to use JCRService only where there was no requirement for new tool content to appear in legacy tools. As we move forwards towards wider JCR adoption it has become clear that there needs to be a way in which new tools can store their content in JCR and have that content accessible for both read and write within tools (e.g. Resources) that continue to use the legacy Content Hosting Service. The post 2.5 components (shown in red above), 'JCR Content Hosting Handler', 'JCR Node Factory Service' and 'Content 2 Wrapper' make this possible and easy to achieve.