Module java.desktop
Package javax.imageio.spi

Class ImageWriterSpi

java.lang.Object
javax.imageio.spi.IIOServiceProvider
javax.imageio.spi.ImageReaderWriterSpi
javax.imageio.spi.ImageWriterSpi
All Implemented Interfaces:
RegisterableService
public abstract class ImageWriterSpi
extends ImageReaderWriterSpi
The service provider interface (SPI) for ImageWriters. For more information on service provider classes, see the class comment for the IIORegistry class.

Each ImageWriterSpi provides several types of information about the ImageWriter class with which it is associated.

The name of the vendor who defined the SPI class and a brief description of the class are available via the getVendorName, getDescription, and getVersion methods. These methods may be internationalized to provide locale-specific output. These methods are intended mainly to provide short, human-writable information that might be used to organize a pop-up menu or other list.

Lists of format names, file suffixes, and MIME types associated with the service may be obtained by means of the getFormatNames, getFileSuffixes, and getMIMEType methods. These methods may be used to identify candidate ImageWriters for writing a particular file or stream based on manual format selection, file naming, or MIME associations.

A more reliable way to determine which ImageWriters are likely to be able to parse a particular data stream is provided by the canEncodeImage method. This methods allows the service provider to inspect the actual image contents.

Finally, an instance of the ImageWriter class associated with this service provider may be obtained by calling the createWriterInstance method. Any heavyweight initialization, such as the loading of native libraries or creation of large tables, should be deferred at least until the first invocation of this method.

See Also:
IIORegistry, ImageTypeSpecifier, ImageWriter

  • Field Details

    • STANDARD_OUTPUT_TYPE

      @Deprecated public static final Class<?>[] STANDARD_OUTPUT_TYPE
      Deprecated.
      Instead of using this field, directly create the equivalent array { ImageOutputStream.class }.
      A single-element array, initially containing ImageOutputStream.class, to be returned from getOutputTypes.

    • outputTypes

      protected Class<?>[] outputTypes
      An array of Class objects to be returned from getOutputTypes, initially null.

    • readerSpiNames

      protected String[] readerSpiNames
      An array of strings to be returned from getImageReaderSpiNames, initially null.

  • Constructor Details

    • ImageWriterSpi

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

    • ImageWriterSpi

      public ImageWriterSpi​(String vendorName, String version, String[] names, String[] suffixes, String[] MIMETypes, String writerClassName, Class<?>[] outputTypes, String[] readerSpiNames, boolean supportsStandardStreamMetadataFormat, String nativeStreamMetadataFormatName, String nativeStreamMetadataFormatClassName, String[] extraStreamMetadataFormatNames, String[] extraStreamMetadataFormatClassNames, boolean supportsStandardImageMetadataFormat, String nativeImageMetadataFormatName, String nativeImageMetadataFormatClassName, String[] extraImageMetadataFormatNames, String[] extraImageMetadataFormatClassNames)
      Constructs an ImageWriterSpi with a given set of values.
      Parameters:
      vendorName - the vendor name, as a non-null String.
      version - a version identifier, as a non-null String.
      names - a non-null array of Strings indicating the format names. At least one entry must be present.
      suffixes - an array of Strings indicating the common file suffixes. If no suffixes are defined, null should be supplied. An array of length 0 will be normalized to null.
      MIMETypes - an array of Strings indicating the format's MIME types. If no suffixes are defined, null should be supplied. An array of length 0 will be normalized to null.
      writerClassName - the fully-qualified name of the associated ImageWriterSpi class, as a non-null String.
      outputTypes - an array of Class objects of length at least 1 indicating the legal output types.
      readerSpiNames - an array Strings of length at least 1 naming the classes of all associated ImageReaders, or null. An array of length 0 is normalized to null.
      supportsStandardStreamMetadataFormat - a boolean that indicates whether a stream metadata object can use trees described by the standard metadata format.
      nativeStreamMetadataFormatName - a String, or null, to be returned from getNativeStreamMetadataFormatName.
      nativeStreamMetadataFormatClassName - a String, or null, to be used to instantiate a metadata format object to be returned from getNativeStreamMetadataFormat.
      extraStreamMetadataFormatNames - an array of Strings, or null, to be returned from getExtraStreamMetadataFormatNames. An array of length 0 is normalized to null.
      extraStreamMetadataFormatClassNames - an array of Strings, or null, to be used to instantiate a metadata format object to be returned from getStreamMetadataFormat. An array of length 0 is normalized to null.
      supportsStandardImageMetadataFormat - a boolean that indicates whether an image metadata object can use trees described by the standard metadata format.
      nativeImageMetadataFormatName - a String, or null, to be returned from getNativeImageMetadataFormatName.
      nativeImageMetadataFormatClassName - a String, or null, to be used to instantiate a metadata format object to be returned from getNativeImageMetadataFormat.
      extraImageMetadataFormatNames - an array of Strings to be returned from getExtraImageMetadataFormatNames. An array of length 0 is normalized to null.
      extraImageMetadataFormatClassNames - an array of Strings, or null, to be used to instantiate a metadata format object to be returned from getImageMetadataFormat. An array of length 0 is normalized to null.
      Throws:
      IllegalArgumentException - if vendorName is null.
      IllegalArgumentException - if version is null.
      IllegalArgumentException - if names is null or has length 0.
      IllegalArgumentException - if writerClassName is null.
      IllegalArgumentException - if outputTypes is null or has length 0.

  • Method Details

    • isFormatLossless

      public boolean isFormatLossless()
      Returns true if the format that this writer outputs preserves pixel data bit-accurately. The default implementation returns true.
      Returns:
      true if the format preserves full pixel accuracy.

    • getOutputTypes

      public Class<?>[] getOutputTypes()
      Returns an array of Class objects indicating what types of objects may be used as arguments to the writer's setOutput method.

      For most writers, which only output to an ImageOutputStream, a single-element array containing ImageOutputStream.class should be returned.

      Returns:
      a non-null array of Class objects of length at least 1.

    • canEncodeImage

      public abstract boolean canEncodeImage​(ImageTypeSpecifier type)
      Returns true if the ImageWriter implementation associated with this service provider is able to encode an image with the given layout. The layout (i.e., the image's SampleModel and ColorModel) is described by an ImageTypeSpecifier object.

      A return value of true is not an absolute guarantee of successful encoding; the encoding process may still produce errors due to factors such as I/O errors, inconsistent or malformed data structures, etc. The intent is that a reasonable inspection of the basic structure of the image be performed in order to determine if it is within the scope of the encoding format. For example, a service provider for a format that can only encode greyscale would return false if handed an RGB BufferedImage. Similarly, a service provider for a format that can encode 8-bit RGB imagery might refuse to encode an image with an associated alpha channel.

      Different ImageWriters, and thus service providers, may choose to be more or less strict. For example, they might accept an image with premultiplied alpha even though it will have to be divided out of each pixel, at some loss of precision, in order to be stored.

      Parameters:
      type - an ImageTypeSpecifier specifying the layout of the image to be written.
      Returns:
      true if this writer is likely to be able to encode images with the given layout.
      Throws:
      IllegalArgumentException - if type is null.

    • canEncodeImage

      public boolean canEncodeImage​(RenderedImage im)
      Returns true if the ImageWriter implementation associated with this service provider is able to encode the given RenderedImage instance. Note that this includes instances of java.awt.image.BufferedImage.

      See the discussion for canEncodeImage(ImageTypeSpecifier) for information on the semantics of this method.

      Parameters:
      im - an instance of RenderedImage to be encoded.
      Returns:
      true if this writer is likely to be able to encode this image.
      Throws:
      IllegalArgumentException - if im is null.

    • createWriterInstance

      public ImageWriter createWriterInstance() throws IOException
      Returns an instance of the ImageWriter implementation associated with this service provider. The returned object will initially be in an initial state as if its reset method had been called.

      The default implementation simply returns createWriterInstance(null).

      Returns:
      an ImageWriter instance.
      Throws:
      IOException - if an error occurs during loading, or initialization of the writer class, or during instantiation or initialization of the writer object.

    • createWriterInstance

      public abstract ImageWriter createWriterInstance​(Object extension) throws IOException
      Returns an instance of the ImageWriter implementation associated with this service provider. The returned object will initially be in an initial state as if its reset method had been called.

      An Object may be supplied to the plug-in at construction time. The nature of the object is entirely plug-in specific.

      Typically, a plug-in will implement this method using code such as return new MyImageWriter(this).

      Parameters:
      extension - a plug-in specific extension object, which may be null.
      Returns:
      an ImageWriter instance.
      Throws:
      IOException - if the attempt to instantiate the writer fails.
      IllegalArgumentException - if the ImageWriter's constructor throws an IllegalArgumentException to indicate that the extension object is unsuitable.

    • isOwnWriter

      public boolean isOwnWriter​(ImageWriter writer)
      Returns true if the ImageWriter object passed in is an instance of the ImageWriter associated with this service provider.
      Parameters:
      writer - an ImageWriter instance.
      Returns:
      true if writer is recognized
      Throws:
      IllegalArgumentException - if writer is null.

    • getImageReaderSpiNames

      public String[] getImageReaderSpiNames()
      Returns an array of Strings containing all the fully qualified names of all the ImageReaderSpi classes that can understand the internal metadata representation used by the ImageWriter associated with this service provider, or null if there are no such ImageReaders specified. If a non-null value is returned, it must have non-zero length.

      The first item in the array must be the name of the service provider for the "preferred" reader, as it will be used to instantiate the ImageReader returned by ImageIO.getImageReader(ImageWriter).

      This mechanism may be used to obtain ImageReaders that will generated non-pixel meta-data (see IIOExtraDataInfo) in a structure understood by an ImageWriter. By reading the image and obtaining this data from one of the ImageReaders obtained with this method and passing it on to the ImageWriter, a client program can read an image, modify it in some way, and write it back out preserving all meta-data, without having to understand anything about the internal structure of the meta-data, or even about the image format.

      Returns:
      an array of Strings of length at least 1 containing names of ImageReaderSpis, or null.
      See Also:
      ImageIO.getImageReader(ImageWriter), ImageReaderSpi.getImageWriterSpiNames()