Java™ Platform
Standard Ed. 6

javax.imageio.spi
Class IIORegistry

java.lang.Object
  extended by javax.imageio.spi.ServiceRegistry
      extended by javax.imageio.spi.IIORegistry

public final class IIORegistry
extends ServiceRegistry

A registry for service provider instances. Service provider classes may be detected at run time by means of meta-information in the JAR files containing them. The intent is that it be relatively inexpensive to load and inspect all available service provider classes. These classes may them be used to locate and instantiate more heavyweight classes that will perform actual work, in this case instances of ImageReader, ImageWriter, ImageTranscoder, ImageInputStream, and ImageOutputStream.

Service providers found on the system classpath (e.g., the jre/lib/ext directory in Sun's implementation of JDK) are automatically loaded as soon as this class is instantiated.

When the registerApplicationClasspathSpis method is called, service provider instances declared in the meta-information section of JAR files on the application class path are loaded. To declare a service provider, a services subdirectory is placed within the META-INF directory that is present in every JAR file. This directory contains a file for each service provider interface that has one or more implementation classes present in the JAR file. For example, if the JAR file contained a class named com.mycompany.imageio.MyFormatReaderSpi which implements the ImageReaderSpi interface, the JAR file would contain a file named:

 META-INF/services/javax.imageio.spi.ImageReaderSpi
 
containing the line:
 com.mycompany.imageio.MyFormatReaderSpi
 

The service provider classes are intended to be lightweight and quick to load. Implementations of these interfaces should avoid complex dependencies on other classes and on native code.

It is also possible to manually add service providers not found automatically, as well as to remove those that are using the interfaces of the ServiceRegistry class. Thus the application may customize the contents of the registry as it sees fit.

For more details on declaring service providers, and the JAR format in general, see the JAR File Specification.


Nested Class Summary
 
Nested classes/interfaces inherited from class javax.imageio.spi.ServiceRegistry
ServiceRegistry.Filter
 
Method Summary
static IIORegistry getDefaultInstance()
          Returns the default IIORegistry instance used by the Image I/O API.
 void registerApplicationClasspathSpis()
          Registers all available service providers found on the application class path, using the default ClassLoader.
 
Methods inherited from class javax.imageio.spi.ServiceRegistry
contains, deregisterAll, deregisterAll, deregisterServiceProvider, deregisterServiceProvider, finalize, getCategories, getServiceProviderByClass, getServiceProviders, getServiceProviders, lookupProviders, lookupProviders, registerServiceProvider, registerServiceProvider, registerServiceProviders, setOrdering, unsetOrdering
 
Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Method Detail

getDefaultInstance

public static IIORegistry getDefaultInstance()
Returns the default IIORegistry instance used by the Image I/O API. This instance should be used for all registry functions.

Each ThreadGroup will receive its own instance; this allows different Applets in the same browser (for example) to each have their own registry.

Returns:
the default registry for the current ThreadGroup.

registerApplicationClasspathSpis

public void registerApplicationClasspathSpis()
Registers all available service providers found on the application class path, using the default ClassLoader. This method is typically invoked by the ImageIO.scanForPlugins method.

See Also:
ImageIO.scanForPlugins(), ClassLoader.getResources(java.lang.String)

Java™ Platform
Standard Ed. 6

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For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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