org.restlet.representation

Class Representation

java.lang.Object

org.restlet.representation.Variant

org.restlet.representation.RepresentationInfo

org.restlet.representation.Representation

Direct Known Subclasses:

ChannelRepresentation, CharacterRepresentation, EmptyRepresentation, FileRepresentation, StreamRepresentation, WrapperRepresentation

public abstract class Representation
extends RepresentationInfo

Current or intended state of a resource. The content of a representation can be retrieved several times if there is a stable and accessible source, like a local file or a string. When the representation is obtained via a temporary source like a network socket, its content can only be retrieved once. The "transient" and "available" properties are available to help you figure out those aspects at runtime.

For performance purpose, it is essential that a minimal overhead occurs upon initialization. The main overhead must only occur during invocation of content processing methods (write, getStream, getChannel and toString).

"REST components perform actions on a resource by using a representation to capture the current or intended state of that resource and transferring that representation between components. A representation is a sequence of bytes, plus representation metadata to describe those bytes. Other commonly used but less precise names for a representation include: document, file, and HTTP message entity, instance, or variant." Roy T. Fielding

Author:

Jerome Louvel

See Also:

Source dissertation

Field Summary

Fields

Modifier and Type	Field and Description
static long	UNKNOWN_SIZE Indicates that the size of the representation can't be known in advance.

Constructor Summary

Constructors

Constructor and Description
Representation() Default constructor.
Representation(MediaType mediaType) Constructor.
Representation(MediaType mediaType, Date modificationDate) Constructor.
Representation(MediaType mediaType, Date modificationDate, Tag tag) Constructor.
Representation(MediaType mediaType, Tag tag) Constructor.
Representation(Variant variant, Date modificationDate) Constructor from a variant.
Representation(Variant variant, Date modificationDate, Tag tag) Constructor from a variant.
Representation(Variant variant, Tag tag) Constructor from a variant.

Method Summary

Methods

Modifier and Type	Method and Description
void	append(Appendable appendable) Appends the representation to an appendable sequence of characters.
long	exhaust() Exhaust the content of the representation by reading it and silently discarding anything read.
long	getAvailableSize() Returns the size effectively available.
abstract ReadableByteChannel	getChannel() Returns a channel with the representation's content. If it is supported by a file, a read-only instance of FileChannel is returned. This method is ensured to return a fresh channel for each invocation unless it is a transient representation, in which case null is returned.
Digest	getDigest() Returns the representation digest if any. Note that when used with HTTP connectors, this property maps to the "Content-MD5" header.
Disposition	getDisposition() Returns the disposition characteristics of the representation.
Date	getExpirationDate() Returns the future date when this representation expire.
Range	getRange() Returns the range where in the full content the partial content available should be applied. Note that when used with HTTP connectors, this property maps to the "Content-Range" header.
abstract Reader	getReader() Returns a characters reader with the representation's content.
SelectionRegistration	getRegistration() Returns the NIO registration of the related channel with its selector.
long	getSize() Returns the total size in bytes if known, UNKNOWN_SIZE (-1) otherwise.
abstract InputStream	getStream() Returns a stream with the representation's content.
String	getText() Converts the representation to a string value.
boolean	hasKnownSize() Indicates if the size of representation is known.
boolean	isAvailable() Indicates if some fresh content is potentially available, without having to actually call one of the content manipulation method like getStream() that would actually consume it.
boolean	isEmpty() Indicates if the representation is empty.
boolean	isSelectable() Indicates if the representation content supports NIO selection.
boolean	isTransient() Indicates if the representation's content is transient, which means that it can be obtained only once.
void	release() Releases the representation and all associated objects like streams, channels or files which are used to produce its content, transient or not.
void	setAvailable(boolean available) Indicates if some fresh content is available.
void	setDigest(Digest digest) Sets the representation digest. Note that when used with HTTP connectors, this property maps to the "Content-MD5" header.
void	setDisposition(Disposition disposition) Sets the disposition characteristics of the representation.
void	setExpirationDate(Date expirationDate) Sets the future date when this representation expire.
void	setListener(ReadingListener readingListener) Sets a listener for NIO read events.
void	setRange(Range range) Sets the range where in the full content the partial content available should be applied. Note that when used with HTTP connectors, this property maps to the "Content-Range" header.
void	setSize(long expectedSize) Sets the expected size in bytes if known, -1 otherwise.
void	setTransient(boolean isTransient) Indicates if the representation's content is transient.
abstract void	write(OutputStream outputStream) Writes the representation to a byte stream.
abstract void	write(WritableByteChannel writableChannel) Writes the representation to a byte channel.
abstract void	write(Writer writer) Writes the representation to a characters writer.

Methods inherited from class org.restlet.representation.RepresentationInfo

getModificationDate, getTag, setModificationDate, setTag

Methods inherited from class org.restlet.representation.Variant

createClientInfo, equals, getCharacterSet, getEncodings, getLanguages, getLocationRef, getMediaType, hashCode, includes, isCompatible, setCharacterSet, setEncodings, setLanguages, setLocationRef, setLocationRef, setMediaType, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

UNKNOWN_SIZE

public static final long UNKNOWN_SIZE

Indicates that the size of the representation can't be known in advance.

See Also:

Constant Field Values

Constructor Detail

Representation

public Representation()

Default constructor.

Representation

public Representation(MediaType mediaType)

Constructor.

Parameters:

mediaType - The media type.

Representation

public Representation(MediaType mediaType,
              Date modificationDate)

Constructor.

Parameters:

mediaType - The media type.

modificationDate - The modification date.

Representation

public Representation(MediaType mediaType,
              Date modificationDate,
              Tag tag)

Constructor.

Parameters:

mediaType - The media type.

modificationDate - The modification date.

tag - The tag.

Representation

public Representation(MediaType mediaType,
              Tag tag)

Constructor.

Parameters:

mediaType - The media type.

tag - The tag.

Representation

public Representation(Variant variant,
              Date modificationDate)

Constructor from a variant.

Parameters:

variant - The variant to copy.

modificationDate - The modification date.

Representation

public Representation(Variant variant,
              Date modificationDate,
              Tag tag)

Constructor from a variant.

Parameters:

variant - The variant to copy.

modificationDate - The modification date.

tag - The tag.

Representation

public Representation(Variant variant,
              Tag tag)

Constructor from a variant.

Parameters:

variant - The variant to copy.

tag - The tag.

Method Detail

append

public void append(Appendable appendable)
            throws IOException

Appends the representation to an appendable sequence of characters. This method is ensured to write the full content for each invocation unless it is a transient representation, in which case an exception is thrown.

Note that getText() is used by the default implementation.

Parameters:

appendable - The appendable sequence of characters.

Throws:

IOException

exhaust

public long exhaust()
             throws IOException

Exhaust the content of the representation by reading it and silently discarding anything read. By default, it relies on getStream() and closes the retrieved stream in the end.

Returns:

The number of bytes consumed or -1 if unknown.

Throws:

IOException

getAvailableSize

public long getAvailableSize()

Returns the size effectively available. This returns the same value as getSize() if no range is defined, otherwise it returns the size of the range using Range.getSize().

Returns:

The available size.

getChannel

public abstract ReadableByteChannel getChannel()
                                        throws IOException

Returns a channel with the representation's content.
If it is supported by a file, a read-only instance of FileChannel is returned.
This method is ensured to return a fresh channel for each invocation unless it is a transient representation, in which case null is returned.

Returns:

A channel with the representation's content.

Throws:

IOException

getDigest

public Digest getDigest()

Returns the representation digest if any.

Note that when used with HTTP connectors, this property maps to the "Content-MD5" header.

Returns:

The representation digest or null.

getDisposition

public Disposition getDisposition()

Returns the disposition characteristics of the representation.

Returns:

The disposition characteristics of the representation.

getExpirationDate

public Date getExpirationDate()

Returns the future date when this representation expire. If this information is not known, returns null.

Note that when used with HTTP connectors, this property maps to the "Expires" header.

Returns:

The expiration date.

getRange

public Range getRange()

Returns the range where in the full content the partial content available should be applied.

Note that when used with HTTP connectors, this property maps to the "Content-Range" header.

Returns:

The content range or null if the full content is available.

getReader

public abstract Reader getReader()
                          throws IOException

Returns a characters reader with the representation's content. This method is ensured to return a fresh reader for each invocation unless it is a transient representation, in which case null is returned. If the representation has no character set defined, the system's default one will be used.

Returns:

A reader with the representation's content.

Throws:

IOException

getRegistration

public SelectionRegistration getRegistration()
                                      throws IOException

Returns the NIO registration of the related channel with its selector. You can modify this registration to be called back when some readable content is available. Note that the listener will keep being called back until you suspend or cancel the registration returned by this method.

Returns:

The NIO registration.

Throws:

IOException

See Also:

isSelectable()

getSize

public long getSize()

Returns the total size in bytes if known, UNKNOWN_SIZE (-1) otherwise. When ranges are used, this might not be the actual size available. For this purpose, you can use the getAvailableSize() method.

Note that when used with HTTP connectors, this property maps to the "Content-Length" header.

Returns:

The size in bytes if known, UNKNOWN_SIZE (-1) otherwise.

See Also:

isEmpty()

getStream

public abstract InputStream getStream()
                               throws IOException

Returns a stream with the representation's content. This method is ensured to return a fresh stream for each invocation unless it is a transient representation, in which case null is returned.

Returns:

A stream with the representation's content.

Throws:

IOException

getText

public String getText()
               throws IOException

Converts the representation to a string value. Be careful when using this method as the conversion of large content to a string fully stored in memory can result in OutOfMemoryErrors being thrown.

Returns:

The representation as a string value.

Throws:

IOException

hasKnownSize

public boolean hasKnownSize()

Indicates if the size of representation is known. It basically means that its size 0 or superior.

Returns:

True if the representation has content.

isAvailable

public boolean isAvailable()

Indicates if some fresh content is potentially available, without having to actually call one of the content manipulation method like getStream() that would actually consume it. Note that when the size of a representation is 0 is a not considered available. However, sometimes the size isn't known until a read attempt is made, so availability doesn't guarantee a non empty content.

This is especially useful for transient representation whose content can only be accessed once and also when the size of the representation is not known in advance.

Returns:

True if some fresh content is available.

isEmpty

public boolean isEmpty()

Indicates if the representation is empty. It basically means that its size is 0.

Returns:

True if the representation has no content.

isSelectable

public boolean isSelectable()

Indicates if the representation content supports NIO selection. In this case, the ext.nio.internal.ConnectionController method can be called to be notified when new content is ready for reading.

Returns:

True if the representation content supports NIO selection.

See Also:

ext.nio.internal.ConnectionController

isTransient

public boolean isTransient()

Indicates if the representation's content is transient, which means that it can be obtained only once. This is often the case with representations transmitted via network sockets for example. In such case, if you need to read the content several times, you need to cache it first, for example into memory or into a file.

Returns:

True if the representation's content is transient.

release

public void release()

Releases the representation and all associated objects like streams, channels or files which are used to produce its content, transient or not. This method must be systematically called when the representation is no longer intended to be used. The framework automatically calls back this method via its connectors on the server-side when sending responses with an entity and on the client-side when sending a request with an entity. By default, it calls the setAvailable(boolean) method with "false" as a value.

Note that for transient socket-bound representations, calling this method after consuming the whole content shouldn't prevent the reuse of underlying socket via persistent connections for example. However, if the content hasn't been read, or has been partially read, the impact should be to discard the remaining content and to close the underlying connections.

Therefore, if you are not interested in the content, or in the remaining content, you should first call the exhaust() method or if this could be too costly, you should instead explicitly abort the parent request and the underlying connections using the Request.abort() method or a shortcut one like ServerResource.abort() or Response.abort().

setAvailable

public void setAvailable(boolean available)

Indicates if some fresh content is available.

Parameters:

available - True if some fresh content is available.

setDigest

public void setDigest(Digest digest)

Sets the representation digest.

Note that when used with HTTP connectors, this property maps to the "Content-MD5" header.

Parameters:

digest - The representation digest.

setDisposition

public void setDisposition(Disposition disposition)

Sets the disposition characteristics of the representation.

Parameters:

disposition - The disposition characteristics of the representation.

setExpirationDate

public void setExpirationDate(Date expirationDate)

Sets the future date when this representation expire. If this information is not known, pass null.

Note that when used with HTTP connectors, this property maps to the "Expires" header.

Parameters:

expirationDate - The expiration date.

setListener

public void setListener(ReadingListener readingListener)

Sets a listener for NIO read events. If the listener is null, it clear any existing listener.

Parameters:

readingListener - The listener for NIO read events.

setRange

public void setRange(Range range)

Sets the range where in the full content the partial content available should be applied.

Note that when used with HTTP connectors, this property maps to the "Content-Range" header.

Parameters:

range - The content range.

setSize

public void setSize(long expectedSize)

Sets the expected size in bytes if known, -1 otherwise. For this purpose, you can use the getAvailableSize() method.

Note that when used with HTTP connectors, this property maps to the "Content-Length" header.

Parameters:

expectedSize - The expected size in bytes if known, -1 otherwise.

setTransient

public void setTransient(boolean isTransient)

Indicates if the representation's content is transient.

Parameters:

isTransient - True if the representation's content is transient.

write

public abstract void write(Writer writer)
                    throws IOException

Writes the representation to a characters writer. This method is ensured to write the full content for each invocation unless it is a transient representation, in which case an exception is thrown.

Note that the class implementing this method shouldn't flush or close the given Writer after writing to it as this will be handled by the Restlet connectors automatically.

Parameters:

writer - The characters writer.

Throws:

IOException

write

public abstract void write(WritableByteChannel writableChannel)
                    throws IOException

Writes the representation to a byte channel. This method is ensured to write the full content for each invocation unless it is a transient representation, in which case an exception is thrown.

Parameters:

writableChannel - A writable byte channel.

Throws:

IOException

write

public abstract void write(OutputStream outputStream)
                    throws IOException

Writes the representation to a byte stream. This method is ensured to write the full content for each invocation unless it is a transient representation, in which case an exception is thrown.

Note that the class implementing this method shouldn't flush or close the given OutputStream after writing to it as this will be handled by the Restlet connectors automatically.

Parameters:

outputStream - The output stream.

Throws:

IOException