com.communote.server.api.core.image

Class ImageProvider

java.lang.Object

com.communote.server.api.core.image.ImageProvider

Direct Known Subclasses:

AttachmentImageProvider, ClientImageProvider, EntityImageProvider, HttpExternalImageProvider, UserImageProvider

public abstract class ImageProvider
extends Object

An image provider loads the unscaled images for a certain image type described by an ImageTypeDescriptor.

Author:

Communote GmbH - http://www.communote.com/

Constructor Summary

Constructors

Constructor and Description
ImageProvider(String identifier, String pathToDefaultImage) Create a new ImageProvider.

Method Summary

Modifier and Type	Method and Description
abstract boolean	canLoad(String imageIdentifier) Test whether a provider can load the image.
String	getDefaultImageMimeType() Get the mime type of the default image
protected long	getDefaultImageResourceLastModificationTimestamp() Get the timestamp of the last modification of the default image resource.
String	getDefaultImageVersionString() The version string of the default image.
String	getIdentifier() Return the identifier of the provider.
int	getTimeToLive() Get the number of seconds until a cached image should expire and thus be reloaded
abstract String	getVersionString(String imageIdentifier) Return a string which represents the version of the image.
boolean	hasDefaultImage(String imageIdentifier) Return whether the provider has a default image for the case when there is no image for a given identifier.
void	imageChanged(String imageIdentifier) Invoked by the ImageManager.imageChanged(String, String, String) to notify the provider about a changed image.
abstract boolean	isAuthorized(String imageIdentifier) Return whether the current user is allowed to access the given image.
abstract boolean	isExternalProvider() Return whether this provider loads image from an external resource (like another server) and not from the local database or file system.
Image	loadDefaultImage() Load the default image.
abstract Image	loadImage(String imageIdentifier) Load the unscaled image

Methods inherited from class java.lang.Object

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

Constructor Detail

ImageProvider

public ImageProvider(String identifier,
                     String pathToDefaultImage)

Create a new ImageProvider.

Parameters:

identifier - The identifier of the provider. The identifier has to be unique among all providers that are registered for an image type.

pathToDefaultImage - If the path starts with file: it is interpreted as a file URI otherwise it is interpreted as the name of a resource containing the default image. This resource will be loaded with the class loader of this class. If null, there will be no default image.

Method Detail

canLoad

public abstract boolean canLoad(String imageIdentifier)

Test whether a provider can load the image. This should for instance return false if the provider was disabled completely or partially for certain identifiers. Checking whether the identified image exists is not necessary because loadImage(String) will handle it.

Parameters:

imageIdentifier - the identifier of the image

Returns:

whether the image can be loaded

getDefaultImageMimeType

public String getDefaultImageMimeType()
                               throws ImageNotFoundException

Get the mime type of the default image

Returns:

the mime type

Throws:

ImageNotFoundException - if there is no (valid) default image

getDefaultImageResourceLastModificationTimestamp

protected long getDefaultImageResourceLastModificationTimestamp()

Get the timestamp of the last modification of the default image resource. This method is used by getDefaultImageVersionString() when the default image exists and is resource that should be loaded with the class loader. This implementation returns the build-timestamp of the application.

Returns:

the timestamp of the last modification

getDefaultImageVersionString

public String getDefaultImageVersionString()
                                    throws ImageNotFoundException

The version string of the default image.

Returns:

the version string

Throws:

ImageNotFoundException - in case there is no default image

See Also:

getVersionString(String)

getIdentifier

public String getIdentifier()

Return the identifier of the provider. The identifier has to be unique among all providers that are registered for an image type.

Returns:

the identifier of the provider

getTimeToLive

public int getTimeToLive()

Get the number of seconds until a cached image should expire and thus be reloaded

Returns:

time to live in the cache

getVersionString

public abstract String getVersionString(String imageIdentifier)
                                 throws AuthorizationException,
                                        ImageNotFoundException

Return a string which represents the version of the image. Whenever an image is modified the version string should change. An example of a version string could be the timestamp of the last modification.
This method is called by the image manager from a method with the same name. The method of the image manager is intended to be called during image URL creation to get an image URL reflecting the latest image version. Since an image URL is usually rendered along with other content, this method should return quickly. The actual image retrieval (download) one the other hand which is done by loadImage can take longer.

Parameters:

imageIdentifier - the identifier of the image

Returns:

the version string of the image.

Throws:

ImageNotFoundException - in case there is no image for the imageIdentifier

AuthorizationException - in case the current user is not allowed to access the image

hasDefaultImage

public boolean hasDefaultImage(String imageIdentifier)

Return whether the provider has a default image for the case when there is no image for a given identifier. This implementation will return true if the resource identified by the constructor parameter pathToDefaultImage exists.

Parameters:

imageIdentifier - the identifier for which no image was found

Returns:

whether there is a default image

imageChanged

public void imageChanged(String imageIdentifier)

Invoked by the ImageManager.imageChanged(String, String, String) to notify the provider about a changed image. The provider can use this method to reset internal caches. The default implementation does nothing.

Parameters:

imageIdentifier - the identifier of the changed image. Can be null in the case that all images have changed.

isAuthorized

public abstract boolean isAuthorized(String imageIdentifier)

Return whether the current user is allowed to access the given image.

Parameters:

imageIdentifier - identifier of the image

Returns:

True, if the user is allowed to access the image.

isExternalProvider

public abstract boolean isExternalProvider()

Return whether this provider loads image from an external resource (like another server) and not from the local database or file system.

Returns:

true, if it is a provider for external images

loadDefaultImage

public Image loadDefaultImage()
                       throws ImageNotFoundException

Load the default image.

Returns:

the default image

Throws:

ImageNotFoundException - in case there is no default image.

loadImage

public abstract Image loadImage(String imageIdentifier)
                         throws ImageNotFoundException,
                                AuthorizationException

Load the unscaled image

Parameters:

imageIdentifier - The identifier of the image

Returns:

The image.

Throws:

ImageNotFoundException - in case there is no image for the imageIdentifier or loading failed

AuthorizationException - in case the current user is not allowed to access the image