Accessing File System Resources (org.apache.sling.fsresource)

Introduction

The Apache Sling File System Resource Provider provides access to the operating system's file system through the Sling ResourceResolver. Multiple locations may be mapped into the resource tree by configuring the file system location and the resource tree root path for each location to be mapped. The provider supports mapping folders and files as binaries, and content structures stored in JSON files or FileVault XML format.

To activate this feature, install the org.apache.sling.fsresource bundle. You can get it from the Sling downloads page or from Maven Central.

Currently two major versions are maintained - choose the correct version depending on your Sling environment:

• fsresource 2.x (trunk): compatible with Apache Sling API 2.11 and Apache Sling Resource Resolver 1.5.18 or above.
• fsresource 1.x (branch): compatible with Apache Sling API 2.4 and Apache Sling Resource Resolver 1.1.0 or above.

Resource Types

Files and directories are mapped into the resource tree as regular Resource instances whose resource type depends on the actual nature of the mapped file system resource:

• Regular files are assigned the nt:file resource type
• Directories are assigned the nt:folder resource type

Content stored in JSON or FileVault XML files are mapped with the resource type stored in the files. If a resource type is missing nt:unstructured is used as fallback.

Adapters

File system resources extend from Sling's AbstractResource class and thus are adaptable to any type for which an AdapterFactory is registered supporting file system resources. In addition File system Resources support the following adapters natively:

• java.io.File -- The Java file object providing access to the file system file
• java.net.URL -- A valid file:// URL to the file. This URL is derived from the java.io.File object by calling the File.toURI().toURL() sequence.
• java.io.InputStream -- If the java.io.File can be read from (as per File.canRead() an InputStream to read from the file is returned.

Configuration

The File System Resource Provider is configured with OSGi Configuration Admin factory configurtions whose factory PID is org.apache.sling.fsprovider.internal.FsResourceProvider. Configuration can be managed using the OSGi Configuration Admin API, through the Web Console or by any other means supporting Configuration Admin configurations. Each configuration "mounts" a specific file system path into the resource hierarchy.

Which files are mounted depends on the 'File system layout' configuration parameter:

• FILES_FOLDERS (default): Support only files and folders (classic mode).
• INITIAL_CONTENT: Sling-Initial-Content filesystem layout, supports file and folders ant content files in JSON and jcr.xml format.
• FILEVAULT_XML: FileVault XML format (expanded content package).

Configuration parameters for each mapping:

FILES_FOLDERS file system layout

The mode maps only files and folders. This was the only mode supported in fsresource versions before 1.3.

Notes:

• No caching is used for this mode.
• Resource events are sent when file oder folder changes are detected.

INITIAL_CONTENT file system layout

The mode maps files and folders, and content files stored in JSON or jcr.xml files. The layout has to match the conventions of the Apache Sling JCR Content Loader. The bundle header Sling-Initial-Content defines where and how the content should be loaded to.

This mode is best use together with the Maven Sling Plugin, which automatically creates the appropriate File System Resource Provider configurations for a Maven bundle project containing content structures. For each path an individual configuration is created.

Usage - deploy OSGi bundle from current maven project and register the appropriate OSGi configuration mappings:

$ mvn -Dsling.mountByFS=true sling:install

Only register the appropriate mappings:

$ mvn sling:fsmount

Remove the mappings:

$ mvn sling:fsunmount

Notes:

• The content of JSON or jcr.xml files is cached in-memory until it changes.
• Resource events are sent when file oder folder changes are detected. When a JSON or jcr.xml file is changed resource events are sent for each resource contained in this file.
• When 'overwrite:=true' is not set for a path in the Sling-Initial-Content header the resource provider falls back to the parent resource provider (e.g. JCR repository) if a requested resource is not find in the file system (version 2.x, with version 1.x this always happens).

FILEVAULT_XML file system layout

The mode maps an maven project containing an expanded content package which uses the Jackrabbit FileVault XML layout in the running Sling instance. The existing of a filter file META-INF/vault/filter.xml is mandatory.

This mode is best use together with the Maven Sling Plugin, which automatically creates the appropriate File System Resource Provider configurations. For each path defined in the filter.xml one mapping configuration is created. The include/exclude definitions are respected as well.

Usage - register the appropriate mappings:

$ mvn sling:fsmount

Remove the mappings:

$ mvn sling:fsunmount

Notes:

• The content of .content.xml files is cached in-memory until it changes.
• Resource events are sent when file oder folder changes are detected. When a JSON or jcr.xml file is changed resource events are sent for each resource contained in this file.
• Content excluded by the filter definition is not mounted by the resource provider, if a resource of the relevant path is requested the resource provider falls back to the parent resource provider (e.g. JCR repository).