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ImageInputStreamSpi (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档

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Standard Ed. 6
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javax.imageio.spi
Class ImageInputStreamSpi

java.lang.Object
  extended by javax.imageio.spi.IIOServiceProvider
      extended by javax.imageio.spi.ImageInputStreamSpi
All Implemented Interfaces:
RegisterableService
public abstract class ImageInputStreamSpi
extends IIOServiceProvider

The service provider interface (SPI) for ImageInputStreams. For more information on service provider interfaces, see the class comment for the IIORegistry class.

This interface allows arbitrary objects to be "wrapped" by instances of ImageInputStream. For example, a particular ImageInputStreamSpi might allow a generic InputStream to be used as an input source; another might take input from a URL.

By treating the creation of ImageInputStreams as a pluggable service, it becomes possible to handle future input sources without changing the API. Also, high-performance implementations of ImageInputStream (for example, native implementations for a particular platform) can be installed and used transparently by applications.

See Also:
IIORegistry, ImageInputStream

Field Summary
protected  Class<?> inputClass
          A Class object indicating the legal object type for use by the createInputStreamInstance method.
 
Fields inherited from class javax.imageio.spi.IIOServiceProvider
vendorName, version
 
Constructor Summary
protected ImageInputStreamSpi()
          Constructs a blank ImageInputStreamSpi.
  ImageInputStreamSpi(String vendorName, String version, Class<?> inputClass)
          Constructs an ImageInputStreamSpi with a given set of values.
 
Method Summary
 boolean canUseCacheFile()
          Returns true if the ImageInputStream implementation associated with this service provider can optionally make use of a cache file for improved performance and/or memory footrprint.
 ImageInputStream createInputStreamInstance(Object input)
          Returns an instance of the ImageInputStream implementation associated with this service provider.
abstract  ImageInputStream createInputStreamInstance(Object input, boolean useCache, File cacheDir)
          Returns an instance of the ImageInputStream implementation associated with this service provider.
 Class<?> getInputClass()
          Returns a Class object representing the class or interface type that must be implemented by an input source in order to be "wrapped" in an ImageInputStream via the createInputStreamInstance method.
 boolean needsCacheFile()
          Returns true if the ImageInputStream implementation associated with this service provider requires the use of a cache File.
 
Methods inherited from class javax.imageio.spi.IIOServiceProvider
getDescription, getVendorName, getVersion, onDeregistration, onRegistration
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

inputClass

protected Class<?> inputClass
A Class object indicating the legal object type for use by the createInputStreamInstance method.

Constructor Detail

ImageInputStreamSpi

protected ImageInputStreamSpi()
Constructs a blank ImageInputStreamSpi. It is up to the subclass to initialize instance variables and/or override method implementations in order to provide working versions of all methods.

ImageInputStreamSpi

public ImageInputStreamSpi(String vendorName,
                           String version,
                           Class<?> inputClass)
Constructs an ImageInputStreamSpi with a given set of values.

Parameters:
vendorName - the vendor name.
version - a version identifier.
inputClass - a Class object indicating the legal object type for use by the createInputStreamInstance method.
Throws:
IllegalArgumentException - if vendorName is null.
IllegalArgumentException - if version is null.
Method Detail

getInputClass

public Class<?> getInputClass()
Returns a Class object representing the class or interface type that must be implemented by an input source in order to be "wrapped" in an ImageInputStream via the createInputStreamInstance method.

Typical return values might include InputStream.class or URL.class, but any class may be used.

Returns:
a Class variable.
See Also:
createInputStreamInstance(Object, boolean, File)

canUseCacheFile

public boolean canUseCacheFile()
Returns true if the ImageInputStream implementation associated with this service provider can optionally make use of a cache file for improved performance and/or memory footrprint. If false, the value of the useCache argument to createInputStreamInstance will be ignored.

The default implementation returns false.

Returns:
true if a cache file can be used by the input streams created by this service provider.

needsCacheFile

public boolean needsCacheFile()
Returns true if the ImageInputStream implementation associated with this service provider requires the use of a cache File. If true, the value of the useCache argument to createInputStreamInstance will be ignored.

The default implementation returns false.

Returns:
true if a cache file is needed by the input streams created by this service provider.

createInputStreamInstance

public abstract ImageInputStream createInputStreamInstance(Object input,
                                                           boolean useCache,
                                                           File cacheDir)
                                                    throws IOException
Returns an instance of the ImageInputStream implementation associated with this service provider. If the use of a cache file is optional, the useCache parameter will be consulted. Where a cache is required, or not applicable, the value of useCache will be ignored.

Parameters:
input - an object of the class type returned by getInputClass.
useCache - a boolean indicating whether a cache file should be used, in cases where it is optional.
cacheDir - a File indicating where the cache file should be created, or null to use the system directory.
Returns:
an ImageInputStream instance.
Throws:
IllegalArgumentException - if input is not an instance of the correct class or is null.
IllegalArgumentException - if a cache file is needed but cacheDir is non-null and is not a directory.
IOException - if a cache file is needed but cannot be created.
See Also:
getInputClass(), canUseCacheFile(), needsCacheFile()

createInputStreamInstance

public ImageInputStream createInputStreamInstance(Object input)
                                           throws IOException
Returns an instance of the ImageInputStream implementation associated with this service provider. A cache file will be created in the system-dependent default temporary-file directory, if needed.

Parameters:
input - an object of the class type returned by getInputClass.
Returns:
an ImageInputStream instance.
Throws:
IllegalArgumentException - if input is not an instance of the correct class or is null.
IOException - if a cache file is needed but cannot be created.
See Also:
getInputClass()
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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.

Copyright 2006 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.