Class JimfsFileSystem
- All Implemented Interfaces:
Closeable
,AutoCloseable
FileSystem
implementation for Jimfs. Most behavior for the file system is implemented by
its default file system view.
Overview of file system design
JimfsFileSystem
instances are created by JimfsFileSystems
using a user-provided Configuration
. The configuration is used to create the
various classes that implement the file system with the correct settings and to create the file
system root directories and working directory. The file system is then used to create the
Path
objects that all file system operations use.
Once created, the primary entry points to the file system are JimfsFileSystemProvider
, which handles calls to
methods in Files
, and JimfsSecureDirectoryStream
, which provides
methods that are similar to those of the file system provider but which treat relative paths as
relative to the stream's directory rather than the file system's working directory.
The implementation of the methods on both of those classes is handled by the FileSystemView
class, which acts as a view of the file
system with a specific working directory. The file system provider uses the file system's default
view, while each secure directory stream uses a view specific to that stream.
File system views make use of the file system's singleton JimfsFileStore
which handles file creation, storage and
attributes. The file store delegates to several other classes to handle each of these:
FileFactory
handles creation of new file objects.HeapDisk
handles allocation of blocks toRegularFile
instances.FileTree
stores the root of the file hierarchy and handles file lookup.AttributeService
handles file attributes, using a set ofAttributeProvider
implementations to handle each supported file attribute view.
Paths
The implementation ofPath
for the file system is JimfsPath
. Paths are created by a PathService
with help from the file system's configured
PathType
.
Paths are made up of Name
objects, which also serve as
the file names in directories. A name has two forms:
- The display form is used in
Path
fortoString()
. It is also used for determining the equality and sort order ofPath
objects for most file systems. - The canonical form is used for equality of two
Name
objects. This affects the notion of name equality in the file system itself for file lookup. A file system may be configured to use the canonical form of the name for path equality (a Windows-like file system configuration does this, as the real Windows file system implementation uses case-insensitive equality for its path objects.
The canonical form of a name is created by applying a series of normalizations to the original string. These normalization may be either a Unicode normalization (e.g. NFD) or case folding normalization for case-insensitivity. Normalizations may also be applied to the display form of a name, but this is currently only done for a Mac OS X type configuration.
Files
All files in the file system are an instance ofFile
. A file
object contains both the file's attributes and content.
There are three types of files:
Directory
- contains a table linking file names to directory entries.RegularFile
- an in-memory store for raw bytes.SymbolicLink
- contains a path.
JimfsFileChannel
, JimfsInputStream
and JimfsOutputStream
implement the standard
channel/stream APIs for regular files.
JimfsSecureDirectoryStream
handles
reading the entries of a directory. The secure directory stream additionally contains a
FileSystemView
with its directory as the working directory, allowing for operations relative to
the actual directory file rather than just the path to the file. This allows the operations to
continue to work as expected even if the directory is moved.
A directory can be watched for changes using the WatchService
implementation, PollingWatchService
.
Regular files
RegularFile
makes use of a singleton HeapDisk
. A disk is a resizable factory and cache for fixed size blocks of memory. These blocks
are allocated to files as needed and returned to the disk when a file is deleted or truncated.
When cached free blocks are available, those blocks are allocated to files first. If more blocks
are needed, they are created.
Linking
When a file is mapped to a file name in a directory table, it is linked. Each type of file has different rules governing how it is linked.- Directory - A directory has two or more links to it. The first is the link from its parent directory to it. This link is the name of the directory. The second is the self link (".") which links the directory to itself. The directory may also have any number of additional parent links ("..") from child directories back to it.
- Regular file - A regular file has one link from its parent directory by default. However, regular files are also allowed to have any number of additional user-created hard links, from the same directory with different names and/or from other directories with any names.
- Symbolic link - A symbolic link can only have one link, from its parent directory.
Thread safety
All file system operations should be safe in a multithreaded environment. The file hierarchy itself is protected by a file system level read-write lock. This ensures safety of all modifications to directory tables as well as atomicity of operations like file moves. Regular files are each protected by a read-write lock which is obtained for each read or write operation. File attributes are protected by synchronization on the file object itself.-
Field Summary
FieldsModifier and TypeFieldDescriptionprivate @Nullable ExecutorService
private final FileSystemView
private final JimfsFileStore
private final PathService
private final JimfsFileSystemProvider
private final URI
private final UserPrincipalLookupService
private final WatchServiceConfiguration
-
Constructor Summary
ConstructorsConstructorDescriptionJimfsFileSystem
(JimfsFileSystemProvider provider, URI uri, JimfsFileStore fileStore, PathService pathService, FileSystemView defaultView, WatchServiceConfiguration watchServiceConfig) -
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Returns a default thread pool to use for asynchronous file channels when users do not provide an executor themselves.Returns the default view for this file system.Returns the file store for this file system.com.google.common.collect.ImmutableSet
<FileStore> getPathMatcher
(String syntaxAndPattern) (package private) PathService
Returns the path service for this file system.com.google.common.collect.ImmutableSortedSet
<Path> getUri()
Returns the URI for this file system.Returns the working directory path for this file system.boolean
isOpen()
boolean
Returnsfalse
; currently, cannot create a read-only file system.provider()
com.google.common.collect.ImmutableSet
<String> Converts the given URI into a path in this file system.Gets the URI of the given path in this file system.
-
Field Details
-
provider
-
uri
-
fileStore
-
pathService
-
userLookupService
-
defaultView
-
watchServiceConfig
-
defaultThreadPool
-
-
Constructor Details
-
JimfsFileSystem
JimfsFileSystem(JimfsFileSystemProvider provider, URI uri, JimfsFileStore fileStore, PathService pathService, FileSystemView defaultView, WatchServiceConfiguration watchServiceConfig)
-
-
Method Details
-
provider
- Specified by:
provider
in classFileSystem
-
getUri
Returns the URI for this file system. -
getDefaultView
Returns the default view for this file system. -
getSeparator
- Specified by:
getSeparator
in classFileSystem
-
getRootDirectories
- Specified by:
getRootDirectories
in classFileSystem
-
getWorkingDirectory
Returns the working directory path for this file system. -
getPathService
PathService getPathService()Returns the path service for this file system. -
getFileStore
Returns the file store for this file system. -
getFileStores
- Specified by:
getFileStores
in classFileSystem
-
supportedFileAttributeViews
- Specified by:
supportedFileAttributeViews
in classFileSystem
-
getPath
- Specified by:
getPath
in classFileSystem
-
toUri
Gets the URI of the given path in this file system. -
toPath
Converts the given URI into a path in this file system. -
getPathMatcher
- Specified by:
getPathMatcher
in classFileSystem
-
getUserPrincipalLookupService
- Specified by:
getUserPrincipalLookupService
in classFileSystem
-
newWatchService
- Specified by:
newWatchService
in classFileSystem
- Throws:
IOException
-
getDefaultThreadPool
Returns a default thread pool to use for asynchronous file channels when users do not provide an executor themselves. (This is required by the spec of newAsynchronousFileChannel in FileSystemProvider.) -
isReadOnly
public boolean isReadOnly()Returnsfalse
; currently, cannot create a read-only file system.- Specified by:
isReadOnly
in classFileSystem
- Returns:
false
, always
-
isOpen
public boolean isOpen()- Specified by:
isOpen
in classFileSystem
-
close
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Specified by:
close
in classFileSystem
- Throws:
IOException
-