Standard file system and entity functionality is extended by capabilities. The capabilities that a file system and its entities have is decided when the file system is created by adding CapabilityProvider:s to its builder. All file system implementations also have built-in capabilities, see Table 4.1, “File system implementations”.

When mixing some capabilities, the order in which the capability providers are added to the file system may be important. Restrictions are documented in each capability provider's API documentation.

Capabilities are used by first retrieving a capability object from a file system or from an entity. The capability is identified by a capability-specific FileSystemCapabilityType or EntityCapabilityType constant.

Below is an example of how the ECUnixAttributes entity capability can be used to get the creation time for an entity. Entity attributes are explained more in detail in Chapter 12, Entity attributes.

// Use the Unix entity attributes capability to find out when the EFile f was
// created

// First get the capability object for the file
ECUnixAttributes eua =
  f.getCapability(ECTUnixAttributes.TYPE);

long timestamp = eua.getAttributes().getCreationTime();

Most capabilities have their own utility classes that can be used to make the client code shorter and more readable. The example below accomplishes just the same as the previous example, but with less code.

// Use the Unix entity attributes capability utility object to find out when the
// EFile f was created

long timestamp = ECUnixAttributesUtil.getCreationTime(f); 

The name of an entity capability object shows for which entity types it is used. If the name starts with FC, the capability is used for EFile:s. If it starts with DC, it is used for Directory:s. An entity capability name starting with EC is used for all entity types.

FileSystem fs = new RamFileSystemBuilder().
  addCapabilityProvider(
    new GZipCompressionCapabilityProvider()).create();