ImageReaderSpi (Java SE 13 & JDK 13 )
Description: declaration: module: java.desktop, package: javax.imageio.spi, class: ImageReaderSpi
Keywords: javax.imageio.spi.ImageReaderSpi class

Module java.desktop
Package javax.imageio.spi

# Class ImageReaderSpi

java.lang.Object
javax.imageio.spi.IIOServiceProvider
javax.imageio.spi.ImageReaderWriterSpi
javax.imageio.spi.ImageReaderSpi

All Implemented Interfaces:
  `RegisterableService`

    public abstract class ImageReaderSpi
    extends ImageReaderWriterSpi

The service provider interface (SPI) for `ImageReader`s. 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 `ImageReader`s 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 `ImageReader`s 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 Summary

  Fields
  Modifier and Type | Field | Description
  --- | --- | ---
  `protected Class<?>[]` | `inputTypes` | An array of `Class` objects to be returned from `getInputTypes`, initially `null`.
  `static Class<?>[]` | `STANDARD_INPUT_TYPE` | Deprecated. Instead of using this field, directly create the equivalent array `{ ImageInputStream.class }`.
  `protected String[]` | `writerSpiNames` | An array of strings to be returned from `getImageWriterSpiNames`, initially `null`.

  ### Fields declared in class javax.imageio.spi.ImageReaderWriterSpi

  `extraImageMetadataFormatClassNames, extraImageMetadataFormatNames, extraStreamMetadataFormatClassNames, extraStreamMetadataFormatNames, MIMETypes, names, nativeImageMetadataFormatClassName, nativeImageMetadataFormatName, nativeStreamMetadataFormatClassName, nativeStreamMetadataFormatName, pluginClassName, suffixes, supportsStandardImageMetadataFormat, supportsStandardStreamMetadataFormat`

  ### Fields declared in class javax.imageio.spi.IIOServiceProvider

  `vendorName, version`

- ## Constructor Summary

  Constructors
  Modifier | Constructor | Description
  --- | --- | ---
  `protected` | `ImageReaderSpi()` | Constructs a blank `ImageReaderSpi`.
  `` | `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.

- ## Method Summary

  Modifier and Type | Method | Description
  --- | --- | ---
  `abstract boolean` | `canDecodeInput​(Object source)` | Returns `true` if the supplied source object appears to be of the format supported by this reader.
  `ImageReader` | `createReaderInstance()` | Returns an instance of the `ImageReader` implementation associated with this service provider.
  `abstract ImageReader` | `createReaderInstance​(Object extension)` | Returns an instance of the `ImageReader` implementation associated with this service provider.
  `String[]` | `getImageWriterSpiNames()` | Returns an array of `String`s 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 `ImageWriter`s specified.
  `Class<?>[]` | `getInputTypes()` | Returns an array of `Class` objects indicating what types of objects may be used as arguments to the reader's `setInput` method.
  `boolean` | `isOwnReader​(ImageReader reader)` | Returns `true` if the `ImageReader` object passed in is an instance of the `ImageReader` associated with this service provider.

  ### Methods declared in class javax.imageio.spi.ImageReaderWriterSpi

  `getExtraImageMetadataFormatNames, getExtraStreamMetadataFormatNames, getFileSuffixes, getFormatNames, getImageMetadataFormat, getMIMETypes, getNativeImageMetadataFormatName, getNativeStreamMetadataFormatName, getPluginClassName, getStreamMetadataFormat, isStandardImageMetadataFormatSupported, isStandardStreamMetadataFormatSupported`

  ### Methods declared in class javax.imageio.spi.IIOServiceProvider

  `getDescription, getVendorName, getVersion, onDeregistration, onRegistration`

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### 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 Details

  - ### 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 `String`s indicating the format names. At least one entry must be present.
      `suffixes` - an array of `String`s 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 `String`s 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 `String`s naming the classes of all associated `ImageWriter`s, 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 `String`s, or `null`, to be returned from `getExtraStreamMetadataFormatNames`. An array of length 0 is normalized to `null`.
      `extraStreamMetadataFormatClassNames` - an array of `String`s, 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 `String`s to be returned from `getExtraImageMetadataFormatNames`. An array of length 0 is normalized to `null`.
      `extraImageMetadataFormatClassNames` - an array of `String`s, 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 Details

  - ### 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 `ImageReaderSpi`s 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 `String`s 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 `ImageWriter`s 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 `String`s of length at least 1 containing names of `ImageWriterSpi`, or `null`.
    See Also:
      `ImageIO.getImageWriter(ImageReader)`