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META-INF/services directory that is used to list any
service providers that are contained in the file. For each service
provider interface that is implemented by a class stored in the JAR
file, a file whose name is the fully-qualified class name of the
service provider interface is placed within the
services directory. The file should contain the
fully-qualified class names of the implementation classes present
in the JAR file, one per line. For example, if the JAR file
contains a service provider class named
com.mycompany.mypackage.MyImageReaderSpi, which
implements the javax.imageio.spi.ImageReaderSpi
interface, there should be a file named
META-INF/services/javax.imageio.spi.ImageReaderSpi
containing the line
com.mycompany.mypackage.MyImageReaderSpi.
The Image I/O API
will automatically examine any JAR files that are found on the
class path, and identify those that contain Image I/O plug-ins. For
each plug-in found, a single instance of its service provider class
will be instantiated and stored in a run-time registry class,
javax.iamgeio.spi.IIORegistry.
JAR files on the
application class path (i.e., the path set using the
CLASSPATH variable), or elsewhere (e.g., available via
a network URL) may be loaded by the application. They are not
loaded by default in order to minimize startup time.
The
javax.imageio.spi.IIORegistry class may also be used
at run-time to deregister installed plug-ins and to register new
ones. In particular, it is possible to use a
ClassLoader to load a plug-in over the network, which
may then be registered and used exactly like a locally installed
plug-in.
Most applications
should not need to deal directly with the registry. Instead, they
may make use of convenience methods contained within the
javax.imageio.ImageIO class that search for
appropriate plug-ins automatically.
