Class StorageConnector

Object

StorageConnector

All Implemented Interfaces:

Serializable

public class StorageConnector
extends Object
implements Serializable

Information for creating a connection to a Data­Store in read and/or write mode. Storage­Connector wraps an input Object, which can be any of the following types:

• A Path or a File for a file or a directory.
• A URI or a URL to a distant resource.
• A Char­Sequence interpreted as a filename or a URL.
• A Channel, Data­Input, Input­Stream or Reader.
• A Data­Source or a Connection to a JDBC database.
• Any other Data­Store-specific object, for example Netcdf­File.

The get­Storage­As(Class) method provides the storage as an object of the given type, opening the input stream if necessary. This class tries to open the stream only once - subsequent invocation of get­Storage­As(…) may return the same input stream.

This class is used only for discovery of a Data­Store implementation capable to handle the input. Once a suitable Data­Store has been found, the Storage­Connector instance is typically discarded since each data store implementation will use their own input/output objects.

Limitations

This class is not thread-safe. Not only Storage­Connector should be used by a single thread, but the objects returned by get­Storage­As(Class) should also be used by the same thread.

Instances of this class are serializable if the storage object given at construction time is serializable.

Since:

0.3

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_BUFFER_SIZE	The default size (in bytes) of Byte­Buffers created by storage connectors.
static final int	READ_AHEAD_LIMIT	The read-ahead limit for mark operations before probing input streams.

Constructor Summary

Constructors

Constructor	Description
Storage­Connector(Object storage)	Creates a new data store connection wrapping the given input/output object.
Storage­Connector(Storage­Connector parent, Object storage)	Creates a new data store connection which has a sub-component of a larger data store.

Method Summary

Modifier and Type	Method	Description
void	close­All­Except(Object view)	Closes all streams and connections created by this Storage­Connector except the given view.
<S> S	commit(Class<S> type, String format)	Returns the storage as a view of the given type and closes all other views.
String	get­File­Extension()	Returns the filename extension of the input/output object.
<T> T	get­Option(Option­Key<T> key)	Returns the option value for the given key, or null if none.
Object	get­Storage()	Returns the input/output object given at construction time.
<S> S	get­Storage­As(Class<S> type)	Returns the storage as a view of the given type if possible, or null otherwise.
String	get­Storage­Name()	Returns a short name of the input/output object.
final boolean	is­Closed()	Returns whether this storage connector has been closed.
<T> void	set­Option(Option­Key<T> key, T value)	Sets the option value for the given key.
String	to­String()	Returns a string representation of this Storage­Connector for debugging purpose.
boolean	was­Probing­Absent­File()	Returns whether returning the storage would have required the creation of a new file.

Methods inherited from class Object

clone, equals, finalize, get­Class, hash­Code, notify, notify­All, wait, wait, wait

Field Details

DEFAULT_BUFFER_SIZE

public static final int DEFAULT_BUFFER_SIZE

The default size (in bytes) of Byte­Buffers created by storage connectors. Those buffers are typically created when the specified storage object is a File, Path, URL or URI.

The default buffer size is arbitrary and may change in any future Apache SIS version. The current value is 32768. Users can override this value by providing a pre-allocated buffer with Option­Key.BYTE_BUFFER.

Since:

1.4

See Also:

• Option­Key.BYTE_BUFFER
• Constant Field Values

READ_AHEAD_LIMIT

public static final int READ_AHEAD_LIMIT

The read-ahead limit for mark operations before probing input streams. When the storage is an Input­Stream or a Reader, the get­Storage­As(Class) method marks the current position with this "read ahead limit" value for resetting the stream to its original position if the caller does not recognize the stream content. Implementations of the Data­Store­Provider.probe­Content(Storage­Connector) method should avoid reading more bytes or characters from an Input­Stream or from a Reader than this value.

The read ahead limit is arbitrary and may change in any future Apache SIS version. However it is guaranteed to be smaller than or equal to DEFAULT_BUFFER_SIZE. The current value is 8192.

Note for maintainer: this value should not be greater than the Buffered­Input­Stream default buffer size.

Since:

1.5

See Also:

• Input­Stream.mark(int)
• Reader.mark(int)
• Constant Field Values

Constructor Details

StorageConnector

public StorageConnector(Object storage)

Creates a new data store connection wrapping the given input/output object. The object can be of any type, but the class javadoc lists the most typical ones.

Parameters:

storage - the input/output object as a URL, file, image input stream, etc..

StorageConnector

public StorageConnector(StorageConnector parent,
 Object storage)

Creates a new data store connection which has a sub-component of a larger data store. The new storage connector inherits all options that were specified in the parent connector.

Parameters:

parent - the storage connector from which to inherit options.

storage - the input/output object as a URL, file, image input stream, etc..

Since:

1.5

Method Details

setOption

public <T> void setOption(OptionKey<T> key,
 T value)

Sets the option value for the given key. The Storage­Connector class uses the following options, if present:

• Option­Key.ENCODING for decoding characters in an input stream, if needed.
• Option­Key.URL_ENCODING for converting URL to URI or filename, if needed.
• Option­Key.OPEN_OPTIONS for specifying whether the data store shall be read only or read/write.
• Option­Key.BYTE_BUFFER for allowing users to control the byte buffer to be created.

In addition, each Data­Store implementation may use more options.

Type Parameters:

T - the type of option value.

Parameters:

key - the option for which to set the value.

value - the new value for the given option, or null for removing the value.

getOption

public <T> T getOption(OptionKey<T> key)

Returns the option value for the given key, or null if none. This is the value specified by the last call to a set­Option(…) with the given key.

Type Parameters:

T - the type of option value.

Parameters:

key - the option for which to get the value.

Returns:

the current value for the given option, or null if none.

getStorage

public Object getStorage()
                  throws DataStoreException

Returns the input/output object given at construction time. The object can be of any type, but the class javadoc lists the most typical ones.

Returns:

the input/output object as a URL, file, image input stream, etc..

Throws:

Data­Store­Exception - if the storage object has already been used and cannot be reused.

See Also:

• get­Storage­As(Class)

getStorageName

public String getStorageName()

Returns a short name of the input/output object. For example if the storage is a file, this method returns the filename without the path (but including the file extension). The default implementation performs the following choices based on the type of the storage object:

• For Path, File, URI or URL instances, this method uses dedicated API like Path.get­File­Name().
• For Char­Sequence instances, this method gets a string representation of the storage object and returns the part after the last '/' character or platform-dependent name separator.
• For instances of unknown type, this method builds a string representation using the class name. Note that the string representation of unknown types may change in any future SIS version.

Returns:

a short name of the storage object.

getFileExtension

public String getFileExtension()

Returns the filename extension of the input/output object. The default implementation performs the following choices based on the type of the storage object:

• For Path, File, URI, URL or Char­Sequence instances, this method returns the string after the last '.' character in the filename, provided that the '.' is not the first filename character. This may be an empty string if the filename has no extension, but never null.
• For instances of unknown type, this method returns null.

Returns:

the filename extension, or an empty string if none, or null if the storage is an object of unknown type.

getStorageAs

public <S> S getStorageAs(Class<S> type)
                   throws IllegalArgumentException,
DataStoreException

Returns the storage as a view of the given type if possible, or null otherwise. The default implementation accepts the following types:

• String:
  • If the storage object is an instance of the Path, File, URL, URI or Char­Sequence types, returns the string representation of their path.
  • Otherwise, this method returns null.
• Path, URI, URL, File:
  • If the storage object is an instance of the Path, File, URL, URI or Char­Sequence types and that type can be converted to the requested type, returned the conversion result.
  • Otherwise, this method returns null.
• Byte­Buffer:
  • If the storage object can be obtained as described in bullet 2 of the Data­Input section below, then this method returns the associated byte buffer.
  • Otherwise, this method returns null.
• Data­Input:
  • If the storage object is already an instance of Data­Input (including the Image­Input­Stream and Image­Output­Stream types), then it is returned unchanged.
  • Otherwise, if the input is an instance of Byte­Buffer, then an Image­Input­Stream backed by a read-only view of that buffer is created when first needed and returned. The properties (position, mark, limit) of the original buffer are unmodified.
  • Otherwise, if the input is an instance of Path, File, URI, URL, Char­Sequence, Input­Stream or Readable­Byte­Channel, then an Image­Input­Stream backed by a Byte­Buffer is created when first needed and returned.
  • Otherwise, if Image­IO.create­Image­Input­Stream(Object) returns a non-null value, then this value is cached and returned.
  • Otherwise, this method returns null.
• Image­Input­Stream:
  • If the above Data­Input can be created and cast to Image­Input­Stream, returns it.
  • Otherwise this method returns null.
• Input­Stream:
  • If the storage object is already an instance of Input­Stream, then it is returned unchanged.
  • Otherwise, if the above Image­Input­Stream can be created, returns a wrapper around that stream.
  • Otherwise, this method returns null.
• Reader:
  • If the storage object is already an instance of Reader, then it is returned unchanged.
  • Otherwise, if the above Input­Stream can be created, returns an Input­Stream­Reader using the encoding specified by Option­Key.ENCODING if any, or using the system default encoding otherwise.
  • Otherwise, this method returns null.
• Data­Output:
  • If the storage object is already an instance of Data­Output (including the Image­Output­Stream type), then it is returned unchanged.
  • Otherwise, if the output is an instance of Path, File, URI, URL, Char­Sequence, Output­Stream or Writable­Byte­Channel, then an Image­Input­Stream backed by a Byte­Buffer is created when first needed and returned.
  • Otherwise, if Image­IO.create­Image­Output­Stream(Object) returns a non-null value, then this value is cached and returned.
  • Otherwise, this method returns null.
• Image­Output­Stream:
  • If the above Data­Output can be created and cast to Image­Output­Stream, returns it.
  • Otherwise this method returns null.
• Output­Stream:
  • If the above Data­Output can be created and cast to Output­Stream, returns it.
  • Otherwise this method returns null.
• Data­Source:
  • If the storage object is already an instance of Data­Source, then it is returned unchanged.
  • Otherwise, if the storage is convertible to an URI and the URI scheme is "jdbc" (ignoring case), then a data source delegating to Driver­Manager is created when first needed and returned.
  • Otherwise, this method returns null.
• Connection:
  • If the storage object is already an instance of Connection, then it is returned unchanged.
  • Otherwise, if the storage is convertible to a Data­Source, then a connection is obtained when first needed and returned.
  • Otherwise, this method returns null.
• Any other types:
  • If the storage given at construction time is already an instance of the requested type, returns it as-is.
  • Otherwise, this method throws Illegal­Argument­Exception.

Usage for probing operations

Multiple invocations of this method on the same Storage­Connector instance will try to return the same instance on a best effort basis. Consequently, implementations of Data­Store­Provider.probe­Content(Storage­Connector) methods shall not close the stream or database connection returned by this method. In addition, those probe­Content(Storage­Connector) methods are responsible for restoring the stream or byte buffer to its original position on return. For an easier and safer way to ensure that the storage position is not modified, see Data­Store­Provider.probe­Content(Storage­Connector, Class, Prober).

Type Parameters:

S - the compile-time type of the type argument (the source or storage type).

Parameters:

type - the desired type as one of Byte­Buffer, Data­Input, Connection class or other types supported by Storage­Connector subclasses.

Returns:

the storage as a view of the given type, or null if the given type is one of the supported types listed in javadoc but no view can be created for the source given at construction time. In the latter case, was­Probing­Absent­File() can be invoked for determining whether the reason is that the file does not exist but could be created.

Throws:

Illegal­Argument­Exception - if the given type argument is not one of the supported types listed in this javadoc or in subclass javadoc.

Illegal­State­Exception - if this Storage­Connector has been closed.

Data­Store­Exception - if an error occurred while opening a stream or database connection.

See Also:

• get­Storage()
• close­All­Except(Object)
• Data­Store­Provider.probe­Content(Storage­Connector, Class, Prober)

wasProbingAbsentFile

public boolean wasProbingAbsentFile()

Returns whether returning the storage would have required the creation of a new file. This method may return true if all the following conditions are true:

• The options given to this Storage­Connector include Standard­Open­Option.CREATE or CREATE_NEW.
• The get­Storage­As(…) and was­Probing­Absent­File() calls happened in the context of Data­Stores probing the storage content in order to choose a Data­Store­Provider.
• A previous get­Storage­As(Class) call requested some kind of input stream (e.g. Input­Stream, Image­Input­Stream, Data­Input, Reader).
• One of the following conditions is true:
  • The input stream is empty.
  • The storage is an object convertible to a Path and the file identified by that path does not exist.

If all above conditions are true, then get­Storage­As(Class) returns null instead of creating a new empty file. In such case, Data­Store­Provider may use this was­Probing­Absent­File() method for deciding whether to report Probe­Result.SUPPORTED or Probe­Result.UNSUPPORTED_STORAGE.

Rational

When the file does not exist and the CREATE or CREATE_NEW option is provided, get­Storage­As(…) would normally create a new empty file. However this behavior is modified during probing (the first condition in above list) because newly created files are empty and probing empty files may result in EOFException to be thrown or in providers declaring that they do not support the storage.

IF the CREATE or CREATE_NEW options were not provided, then probing the storage content of an absent file will rather throw No­Such­File­Exception or File­Not­Found­Exception. So this method is useful only for Data­Store having write capabilities.

Returns:

whether returning the storage would have required the creation of a new file.

Since:

1.4

commit

public <S> S commit(Class<S> type,
 String format)
             throws IllegalArgumentException,
DataStoreException

Returns the storage as a view of the given type and closes all other views. Invoking this method is equivalent to invoking get­Storage­As(Class) followed by close­All­Except(Object) except that the latter method is always invoked (in a way similar to "try with resource") and that this method never returns null.

Type Parameters:

S - the compile-time type of the type argument (the source or storage type).

Parameters:

type - the desired type as one of the types documented in get­Storage­As(Class) (example: Byte­Buffer, Data­Input, Connection).

format - short name or abbreviation of the data format (e.g. "CSV", "GML", "WKT", etc). Used for information purpose in error messages if needed.

Returns:

the storage as a view of the given type. Never null.

Throws:

Illegal­Argument­Exception - if the given type argument is not one of the supported types.

Illegal­State­Exception - if this Storage­Connector has been closed.

Data­Store­Exception - if an error occurred while opening a stream or database connection.

Since:

1.2

See Also:

• get­Storage­As(Class)
• close­All­Except(Object)

closeAllExcept

public void closeAllExcept(Object view)
                    throws DataStoreException

Closes all streams and connections created by this Storage­Connector except the given view. This method closes all objects created by the get­Storage­As(Class) method except the given view. If view is null, then this method closes everything including the storage if it is closeable.

This method is invoked when a suitable Data­Store has been found - in which case the view used by the data store is given in argument to this method - or when no suitable Data­Store has been found - in which case the view argument is null.

This Storage­Connector instance shall not be used anymore after invocation of this method.

Parameters:

view - the view to leave open, or null if none.

Throws:

Data­Store­Exception - if an error occurred while closing the stream or database connection.

See Also:

• get­Storage­As(Class)
• Data­Store­Provider.open(Storage­Connector)

isClosed

public final boolean isClosed()

Returns whether this storage connector has been closed. If this method returns true, then any call to get­Storage­As(Class) will throw Illegal­State­Exception.

Returns:

true if this storage connector is closed.

Since:

1.5

toString

public String toString()

Returns a string representation of this Storage­Connector for debugging purpose. This string representation is for diagnostic and may change in any future version.

Overrides:

to­String in class Object

Returns:

a string representation of this Storage­Connector for debugging purpose.