eu.fbk.knowledgestore.filestore

Interface FileStore

All Superinterfaces:

AutoCloseable, Closeable, Component

All Known Implementing Classes:

ForwardingFileStore, GzippedFileStore, HadoopFileStore, LoggingFileStore, MultiFileStore, SynchronizedFileStore

public interface FileStore
extends Component

A storage for resource files, supporting CRUD operations.

A FileStore abstracts the way resource files are stored in the KnowledgeStore allowing different implementations to be plugged in. A FileStore stores a list of files each identified by a filename, with no (visible) directory structure. Files can be listed ( list()), written (write(String)), read ( read(String)) or deleted ( delete(String)), but not modified after they are written the first time. Note that a FileStore obeys the general contract and lifecycle of Component.

Method Summary

Modifier and Type	Method and Description
void	delete(String filename) Deletes a file on the FileStore.
Stream<String>	list() Lists all the files stored on the FileStore.
InputStream	read(String filename) Read a file stored on the FileStore.
OutputStream	write(String filename) Writes a new file to the FileStore.

Methods inherited from interface eu.fbk.knowledgestore.runtime.Component

close, init

Method Detail

read

InputStream read(String filename)
          throws FileMissingException,
                 IOException

Read a file stored on the FileStore. The method returns an InputStream over the content of the file, starting from its first byte. Sequential access and forward seeking ( InputStream.skip(long)) are supported. Note that multiple concurrent read operations on the same file are allowed.

Parameters:

filename - the name of the file

Returns:

an InputStream allowing access to the content of the file

Throws:

FileMissingException - in case no file exists for the name specified, resulting either from a caller error or from an external modification (deletion) to the FileStore

IOException - in case the file cannot be accessed for whatever reason, with no implication on the fact that the file exists or does not exist (e.g., the whole FileStore may temporarily be not accessible)

write

OutputStream write(String filename)
            throws FileExistsException,
                   IOException

Writes a new file to the FileStore. The method creates a file with the name specified, and returns an OutputStream that can be used to write the content of the file. Writing is completed by closing that stream, which forces written data to be flushed to disk; errors in writing the file may result in the stream being forcedly closed and a truncated file to be written. The file being written may be listed by list() (depending on the FileStore implementation) but should not be accessed for read or deletion until writing is completed; the consequences of doing so are not specified.

Parameters:

filename - the name of the file

Returns:

an OutputStream where the content of the file can be written to

Throws:

FileExistsException - in case a file with the same name already exists, resulting either from a caller error or from an external modification (file creation) to the FileStore.

IOException - in case the file cannot be created for whatever reason, with no implication on the fact that another file with the same name already exists

delete

void delete(String filename)
     throws FileMissingException,
            IOException

Deletes a file on the FileStore. An exception is thrown if the file specified does not exist. After the method returns, the file cannot be accessed anymore from read(String) or delete(String). Deleting a file being read is allowed and eventually results in the deletion of the file; whether the concurrent read operation fails or is permitted to complete is an implementation detail.

Parameters:

filename - the name of the file

Throws:

FileMissingException - in case the file specified does not exist, possibly because of an external modification to the FileStore

IOException - in case the file cannot be accessed for whatever reason, with no implication on the fact that the file specified actually exists

list

Stream<String> list()
             throws IOException

Lists all the files stored on the FileStore. The method returns a Stream supporting streaming access to the names of the files stored in the FileStore. Concurrent modifications to the FileStore (write(String), delete(String)) may be supported, depending on the implementation: in that case, the stream may either reflect the status before or after the concurrent modification.

Returns:

a stream over the names of the files stored in the FileStore

Throws:

IOException - in case of failure, for whatever reason