Apache Sling provides support for initial content loading into a repository and for registering node types. The sling-jcr-contentloader bundle provides loading of content from a bundle into the repository and the sling-jcr-base bundle provides node type registration.
Bundles can provide initial content, which is loaded into the repository when the bundle has entered the started state. Such content is expected to be contained in the bundles accessible through the Bundle entry API methods. Content to be loaded is declared in the Sling-Initial-Content bundle manifest header. This header takes a comma-separated list of bundle entry paths. Each entry and all its child entries are accessed and entered into starting with the child entries of the listed entries.
Adding this content preserves the paths of the entries as show in this table, which assumes a Sling-Initial-Content header entry of SLING-INF/content:
Bundle entries are installed as follows:
|Entry Type||Installation method|
|Directory||Created as a node of type nt:folder unless a content definition file of the same name exists in the same directory as the directory to be installed. Example: A directory SLING-INF/content/dir is installed as node /dir of type nt:folder unless a SLING-INF/content/dir.xml or SLING-INF/content/dir.json file exists which defines the content for the /dir node.|
|File||Unless the file is a content definition file (see below) an nt:file node is created for the file and an nt:resource node is created as its jcr:content child node to take the contents of the bundle file. The properties of the nt:resource node are set from file information as available. If the file is a content definition file, the content is created as defined in the file. See below for the content definition file specification.|
It is possible to modify the intial content loading default behaviour by using certain optional directives. Directives should be specified separated by semicolon. They are defined as follows:
|overwrite||overwrite:=(true|false)||false||The overwrite directive specifies if content nodes should be overwritten or just initially added. If this is true, existing nodes are deleted and a new node is created in the same place.|
|overwriteProperties||overwriteProperties:=(true|false)||false||The overwriteProperties directive specifying if content properties should be overwritten or just initially added.|
|uninstall||uninstall:=(true|false)||overwrite||The uninstall directive specifies if content should be uninstalled when bundle is unregistered. This value defaults to the value of the overwrite directive.|
|path||path:=/target/location||/||The path directive specifies the target node where initial content will be loaded. If the path does not exist yet in the repository, it is created by the content loader. The intermediate nodes are of type nt:folder.|
|checkin||checkin:=(true|false)||false||The checkin directive specifies whether versionable nodes should be checked in.|
|ignoreImportProviders||ignoreImportProviders:=list of extensions||empty||This directive can be used to not run one of the configured extractors (see below).|
Examples of these directives uses could be (assumes a Sling-Initial-Content header entry of SLING-INF/content):
|SLING-INF/content/home;overwrite:=true;uninstall:=true||Overwrites already existing content in /home and uninstalls the content when the bundle is unregistered.|
|SLING-INF/content/home;overwriteProperties:=true||Overwrites properties of existing content in /home.|
|SLING-INF/content/home;path:=/sites/sling_website||if /sites/sling_website exists it loads the content into it. Otherwise, it loads the content into root node /.|
|SLING-INF/content/home;checkin:=true||After content loading, versionable nodes are checked in.|
Repository items to be loaded into the repository, when the bundle is first installed, may be defined in four ways:
- XML descriptor files
- JSON descriptor files
Depending on the bundle entry found in the location indicated by the Sling-Initial-Content bundle manifest header, nodes are created (and/or updated) as follows:
Unless a node with the name of the directory already exists or has been defined in an XML or JSON descriptor file (see below) a directory is created as a node with the primary node type "nt:folder" in the repository.
Unless a node with the name of the file already exists or has been defined in an XML or JSON descriptor file (see below) a file is created as two nodes in the repository. The node bearing the name of the file itself is created with the
primary node type "nt:file". Underneath this file node, a resource node with the primary node type "nt:resource" is created, which is set to the contents of the file.
The MIME type is derived from the file name extension by first trying to resolve it from the Bundle entry URL. If this does not resolve to a MIME type, the Sling MIME type resolution service is used to try to find a mime type. If all fals, the MIME type is defaulted to "application/octet-stream".
Nodes, Properties and in fact complete subtrees may be described in XML files using either the JCR SystemView format, or the format described below. In either case, the file must have the .xml extension.
By writing an XSLT stylesheet file, you can use whatever XML format you prefer. The XML file references an XSLT stylesheet by using the xml-stylesheet processing instruction:
The my-transform.xsl file is then responsible for translating your format into one of the supported XML formats:
Nodes, Properties and in fact complete subtrees may be described in JSON files using the following skeleton structure (see http://www.json.org or information on the syntax of JSON). The name of parent node is taken from the file name. :
By default, the sling-jcr-contentloader bundle tries to extract certain file types during content loading. These include json, xml, zip, and jar files. Therefore all available extractors are used for content processing. However if some files should be put into the repository unextracted, the ignoreImportProviders directive can be used with a comma separated list of extensions that should not be extracted, like ignoreImportProviders:="jar,zip". Please note that the value needs to be put into quotation marks if more than one value is used like in the example.
By default, initial content will be loaded into the default workspace. To override this, add a Sling-Initial-Content-Workspace bundle manifest header to specify the manifest. Note that all content from a bundle will be loaded into the same workspace.
The sling-jcr-base bundle provides low-level repository operations which are at the heart of the functionality of Sling:
- Node Type Definitions - The class org.apache.sling.content.jcr.base.NodeTypeLoader provides methods to register custom node types with a repository given a repository session and a node type definition file in CND format. This class is also used by this bundle to register node types on behalf of other bundles.
Bundles may list node type definition files in CND format in the Sling-Nodetypes bundle header. This header is a comma-separated list of resources in the respective bundle. Each resource is taken and fed to the NodeTypeLoader to define the node types.
After a bundle has entered the resolved state, the node types listed in the Sling-Nodetypes bundle header are registered with the repository.
Node types installed by this mechanism will never be removed again by the sling-jcr-base bundle.
Starting with revision 911430, re-registration of existing node types is enabled by default. To disable this, add ;rereigster:=false to the resource names for which re-registration should be disabled.
|Support for re-registration of node types is relatively limited. In Jackrabbit, for example, only "trivial" changes are allowed.|
The initial content found in the sling-test folder of the launchpad initial content is verified by the InitialContentTest when running the launchpad/testing integration tests.
Those tests can be used as verified examples of initial content loading. Contributions are welcome to improve the coverage of those tests.