Module java.desktop
Package javax.imageio.spi

Class ImageReaderSpi

  • All Implemented Interfaces:
    RegisterableService

    public abstract class ImageReaderSpi
extends ImageReaderWriterSpi
    The service provider interface (SPI) for ImageReaders. For more information on service provider classes, see the class comment for the IIORegistry class.

    Each ImageReaderSpi provides several types of information about the ImageReader 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-readable 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 getMIMETypes methods. These methods may be used to identify candidate ImageReaders for decoding a particular file or stream based on manual format selection, file naming, or MIME associations (for example, when accessing a file over HTTP or as an email attachment).

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

    Finally, an instance of the ImageReader class associated with this service provider may be obtained by calling the createReaderInstance 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, ImageReader

    • Field Detail

      • STANDARD_INPUT_TYPE

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

      • inputTypes

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

      • writerSpiNames

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

    • Constructor Detail

      • ImageReaderSpi

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

      • ImageReaderSpi

        public ImageReaderSpi​(String vendorName,
                      String version,
                      String[] names,
                      String[] suffixes,
                      String[] MIMETypes,
                      String readerClassName,
                      Class<?>[] inputTypes,
                      String[] writerSpiNames,
                      boolean supportsStandardStreamMetadataFormat,
                      String nativeStreamMetadataFormatName,
                      String nativeStreamMetadataFormatClassName,
                      String[] extraStreamMetadataFormatNames,
                      String[] extraStreamMetadataFormatClassNames,
                      boolean supportsStandardImageMetadataFormat,
                      String nativeImageMetadataFormatName,
                      String nativeImageMetadataFormatClassName,
                      String[] extraImageMetadataFormatNames,
                      String[] extraImageMetadataFormatClassNames)
        Constructs an ImageReaderSpi 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 MIME types are defined, null should be supplied. An array of length 0 will be normalized to null.
        readerClassName - the fully-qualified name of the associated ImageReader class, as a non-null String.
        inputTypes - a non-null array of Class objects of length at least 1 indicating the legal input types.
        writerSpiNames - an array Strings naming the classes of all associated ImageWriters, 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 readerClassName is null.
        IllegalArgumentException - if inputTypes is null or has length 0.

    • Method Detail

      • getInputTypes

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

        For most readers, which only accept input from an ImageInputStream, a single-element array containing ImageInputStream.class should be returned.

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

      • canDecodeInput

        public abstract boolean canDecodeInput​(Object source)
                                throws IOException
        Returns true if the supplied source object appears to be of the format supported by this reader. Returning true from this method does not guarantee that reading will succeed, only that there appears to be a reasonable chance of success based on a brief inspection of the stream contents. If the source is an ImageInputStream, implementations will commonly check the first several bytes of the stream for a "magic number" associated with the format. Once actual reading has commenced, the reader may still indicate failure at any time prior to the completion of decoding.

        It is important that the state of the object not be disturbed in order that other ImageReaderSpis can properly determine whether they are able to decode the object. In particular, if the source is an ImageInputStream, a mark/reset pair should be used to preserve the stream position.

        Formats such as "raw," which can potentially attempt to read nearly any stream, should return false in order to avoid being invoked in preference to a closer match.

        If source is not an instance of one of the classes returned by getInputTypes, the method should simply return false.

        Parameters:
        source - the object (typically an ImageInputStream) to be decoded.
        Returns:
        true if it is likely that this stream can be decoded.
        Throws:
        IllegalArgumentException - if source is null.
        IOException - if an I/O error occurs while reading the stream.

      • createReaderInstance

        public ImageReader createReaderInstance​()
                                 throws IOException
        Returns an instance of the ImageReader 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 createReaderInstance(null).

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

      • createReaderInstance

        public abstract ImageReader createReaderInstance​(Object extension)
                                          throws IOException
        Returns an instance of the ImageReader 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 MyImageReader(this).

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

      • isOwnReader

        public boolean isOwnReader​(ImageReader reader)
        Returns true if the ImageReader object passed in is an instance of the ImageReader associated with this service provider.

        The default implementation compares the fully-qualified class name of the reader argument with the class name passed into the constructor. This method may be overridden if more sophisticated checking is required.

        Parameters:
        reader - an ImageReader instance.
        Returns:
        true if reader is recognized.
        Throws:
        IllegalArgumentException - if reader is null.

      • getImageWriterSpiNames

        public String[] getImageWriterSpiNames​()
        Returns an array of Strings containing the fully qualified names of all the ImageWriterSpi classes that can understand the internal metadata representation used by the ImageReader associated with this service provider, or null if there are no such ImageWriters 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" writer, as it will be used to instantiate the ImageWriter returned by ImageIO.getImageWriter(ImageReader).

        This mechanism may be used to obtain ImageWriters that will understand the internal structure of non-pixel meta-data (see IIOTreeInfo) generated by an ImageReader. By obtaining this data from the ImageReader and passing it on to one of the ImageWriters obtained with this method, a client program can read an image, modify it in some way, and write it back out while 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 ImageWriterSpi, or null.
        See Also:
        ImageIO.getImageWriter(ImageReader)