The FileSystem interface represents a file system. It contains a directory hierarchy containing EFile and Directory entities, and it has a set of policy and strategy objects. It always holds a reference to the root Directory.
A FileSystem is created from a FileSystemBuilder object[1].
Table 4.1. File system implementations
Capabilities are discussed in Chapter 10, Capabilities
All setter methods of a FileSystemBuilder return the builder object. This makes it possibly to chain setter method invocations together as is shown in many of the examples below.
File systems have an optional name that, if set, should be unique within the current system. [2] The name can be used by applications to identify different file system instances. It is not used by EntityFS at all.
Example 4.1. Creating a file system-backed file system
// Create a file system with default settings except for a custom name FileSystem fs1 = new FSRWFileSystemBuilder(). setName("My first file system"). setRoot(new File("/tmp/fs1")). create(); // Create a file system with no event handling and relaxed validity controls // for entities. (See FSRWFileSystemBuilder API docs.) FileSystem fs2 = new FSRWFileSystemBuilder(). setName("My second file system"). setRoot(new File("/tmp/fs2")). disableEntityValidityControls(). // Enable entity locking enableLocking(). create();
Example 4.2. Creating a Jar file-backed file system on a file in another file system
// fs is another file system EFile jarFile = Directories.getFile(fs.getRootDirectory(), "myapp.jar"); FileSystem jfs = new JarFileSystemBuilder(). setName("My Jar file system"). setJarFile(jarFile). create();
By default, file systems are created with a minimal set of features. This can be tuned by configuring the file system builder differently. Also, the default validity control settings for the file system may be more defensive than what is required by the client. By setting less safe values, the file system's performance may increase somewhat.
The following is a list of common file system builder properties:
accessControllerA file system can use an AccessController to limit access to entities. It can be used by applications to implement their access control policies. See Chapter 13, Access controls. Access controls are disabled by default.
bufferSizeThe size of temporary in-memory buffers used by the file system. Different file system implementations use this for different things. The default value is 8192 bytes.
entityValidityControlStrategyThe strategy used for verifying that entities are still
present in the backend whenever they are used. The default strategy for this is
file system-specific. If it is known when the file system is created that no
other processes will ever modify its contents, this can be disabled by calling
disableEntityValidityControls on the file
system builder.
eventsBy calling enableEvents, a
client can make the entire FileSystem as well as individual entities
Observable for EntityEvent:s. See
Chapter 9, Entity events.
lockAcquiringStrategyThe strategy for acquiring file system
EntityLock:s. See
Chapter 7, Locking and multi-threaded access. Entity locking is
disabled by default. It can be
enabled by calling enableLocking
on the file system builder.
lockCommandExecutorUtility class for locking entity locks in accordance with the
file system's locking strategy. Entity locking is disabled by default. It can be
enabled by calling enableLocking
on the file system builder. See
Chapter 7, Locking and multi-threaded access.
lockAdapterFactoryA factory used for creating locks. Entity locking can be
enabled by calling enableLocking
on the file system builder. See
Chapter 7, Locking and multi-threaded access.
Different file system implementations may also have their own, implementation-specific tunable parameters. For details, see the API documentation for each file system implementation.
File system implementations that use backend resources, for instance the Zip
file system, require that the client closes the file system when it is not
needed anymore. Calling close makes the file
system release all open resources.