us.zuercher.gpx2map.image.netpbm
Class NetpbmImageFactory

java.lang.Object
  us.zuercher.gpx2map.image.netpbm.NetpbmImageFactory

All Implemented Interfaces:

ImageFactory

public class NetpbmImageFactory
extends Object
implements ImageFactory

NetpbmImageFactory is a factory for NetpbmImage objects.

Author:

Stephan Zuercher

Nested Class Summary

private class	NetpbmImageFactory.CanLoadLogicTarget CanLoadLogicTarget implements NetpbmImageFactory.GzipRetryLogicTarget to retrieve the Netpbm magic number from an image file.
private static class	NetpbmImageFactory.ExceptionHolder ExceptionHolder holds an IOException for later throwing.
private class	NetpbmImageFactory.GzipRetryLogic GzipRetryLogic encapsulates the logic of reading Netpbm files that may or may not be gzipped.
private static interface	NetpbmImageFactory.GzipRetryLogicTarget
private class	NetpbmImageFactory.LoadImageLogicTarget LoadImageLogicTarget implements NetpbmImageFactory.GzipRetryLogicTarget to read image data from the input stream.

Field Summary

private static List<ImageFormatDescriptor>	formatDescriptors List of ImageFormatDescriptor objects for our supported formats.
static NetpbmImageFactory	instance NetpbmImageFactory singleton instance.
static ImageFormatDescriptor	PAM_IMAGE_FORMAT_DESCRIPTOR PAM ImageFormatDescriptor.
static ImageFormatDescriptor	PPM_IMAGE_FORMAT_DESCRIPTOR PPM ImageFormatDescriptor.

Constructor Summary

private

NetpbmImageFactory() NetpbmImageFactory is a singleton.

Method Summary

boolean	canLoad(File imageFile) Tests whether the given file contains a supported Netpbm image format.
private boolean	canLoad(NetpbmImageFactory.GzipRetryLogic logic) Tests whether an image's format is supported using the given NetpbmImageFactory.GzipRetryLogic object.
boolean	canLoad(URL imageUrl) Tests whether the given URL refers to a supported Netpbm image format.
private void	closeQuietly(InputStream input) Closes an input stream and silently discards IOExceptions encountered during closure.
List<ImageFormatDescriptor>	getSupportedImageFormats() Returns the ImageFormatDescriptors for image formats supported by this factory.
NetpbmImage	loadImage(File netpbmImageFile) Loads a Netpbm-compatible image from the given filename.
private NetpbmImage	loadImage(NetpbmImageFactory.GzipRetryLogic logic) Loads an image using the given NetpbmImageFactory.GzipRetryLogic object.
NetpbmImage	loadImage(URL netpbmImageUrl) Loads a Netpbm-compatible image from the given URL.
private NetpbmImage	makeImage(InputStream input, NetpbmImageFactory.ExceptionHolder exceptionHolder) Load an image given an input stream.
private BufferedInputStream	makeInputStream(File file, boolean useGzip) Create a input stream from a File.
private BufferedInputStream	makeInputStream(URL url, boolean useGzip) Create a input stream from a URL.
private String	readMagic(InputStream input) Reads the Netpbm magic number from the start of a file.

Methods inherited from class java.lang.Object

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

Field Detail

PAM_IMAGE_FORMAT_DESCRIPTOR

public static final ImageFormatDescriptor PAM_IMAGE_FORMAT_DESCRIPTOR

PAM ImageFormatDescriptor.

PPM_IMAGE_FORMAT_DESCRIPTOR

public static final ImageFormatDescriptor PPM_IMAGE_FORMAT_DESCRIPTOR

PPM ImageFormatDescriptor.

instance

public static final NetpbmImageFactory instance

NetpbmImageFactory singleton instance.

formatDescriptors

private static final List<ImageFormatDescriptor> formatDescriptors

List of ImageFormatDescriptor objects for our supported formats.

Constructor Detail

NetpbmImageFactory

private NetpbmImageFactory()

NetpbmImageFactory is a singleton.

See Also:

instance

Method Detail

getSupportedImageFormats

public List<ImageFormatDescriptor> getSupportedImageFormats()

Returns the ImageFormatDescriptors for image formats supported by this factory.

Specified by:

getSupportedImageFormats in interface ImageFactory

Returns:

the ImageFormatDescriptors for image formats supported by this factory.

canLoad

public boolean canLoad(File imageFile)
                throws IOException

Tests whether the given file contains a supported Netpbm image format.

Specified by:

canLoad in interface ImageFactory

Parameters:

imageFile - the file to test

Returns:

true if the file contains a supported Netpbm image format, false otherwise

Throws:

IOException - if the file cannot be read

canLoad

public boolean canLoad(URL imageUrl)
                throws IOException

Tests whether the given URL refers to a supported Netpbm image format.

Specified by:

canLoad in interface ImageFactory

Parameters:

imageUrl - the URL to test

Returns:

true if the URL refers to a supported Netpbm image format, false otherwise

Throws:

IOException - if the URL cannot be read

canLoad

private boolean canLoad(NetpbmImageFactory.GzipRetryLogic logic)
                 throws IOException

Tests whether an image's format is supported using the given NetpbmImageFactory.GzipRetryLogic object.

Parameters:

logic - Gzip retry logic for a file or URL

Returns:

true if the file's magic number indicates a supported Netpbm image format.

Throws:

IOException - if there's an error reading the image data

loadImage

public NetpbmImage loadImage(File netpbmImageFile)
                      throws IOException,
                             UnknownNetpbmFormatException

Loads a Netpbm-compatible image from the given filename. Image files may optionally be compressed using the gzip format. The factory detects image types and compressed images by attempting to read the magic number from the start of the file. If the magic number is not recognized, the file is reopened with gzip-decompression enabled. If the magic number is still not recognized, an exception if thown.

Specified by:

loadImage in interface ImageFactory

Parameters:

netpbmImageFile - location of a netpbm image

Returns:

an implementation of NetpbmImage

Throws:

IOException - if the file cannot be read or the magic number is not recognized.

UnknownNetpbmFormatException - if the file format is not recognized

loadImage

public NetpbmImage loadImage(URL netpbmImageUrl)
                      throws IOException,
                             UnknownNetpbmFormatException

Loads a Netpbm-compatible image from the given URL. Images may optionally be compressed using the gzip format. The factory detects image types and compressed images by attempting to read the magic number from the start of the file. If the magic number is not recognized, the URL is reopened with gzip-decompression enabled. If the magic number is still not recognized, an exception if thown.

Specified by:

loadImage in interface ImageFactory

Parameters:

netpbmImageUrl - location of a netpbm image

Returns:

an implementation of NetpbmImage

Throws:

IOException - if the file cannot be read or the magic number is not recognized.

UnknownNetpbmFormatException - if the file format is not recognized

loadImage

private NetpbmImage loadImage(NetpbmImageFactory.GzipRetryLogic logic)
                       throws IOException,
                              UnknownNetpbmFormatException

Loads an image using the given NetpbmImageFactory.GzipRetryLogic object.

Parameters:

logic - Gzip retry logic for a file or URL

Returns:

a NetpbmImage loaded by the gzip retry logic

Throws:

IOException - if there's an error reading the image data

UnknownNetpbmFormatException - if the image format is not supported

makeInputStream

private BufferedInputStream makeInputStream(File file,
                                            boolean useGzip)
                                     throws IOException

Create a input stream from a File.

Parameters:

file - the file to read

useGzip - flag controlling use of gzip

Returns:

a BufferedInputStream on file, possibly decompressing gzip

Throws:

IOException - if there's an error opening the file

makeInputStream

private BufferedInputStream makeInputStream(URL url,
                                            boolean useGzip)
                                     throws IOException

Create a input stream from a URL.

Parameters:

url - the URL to read

useGzip - flag controlling use of gzip

Returns:

a BufferedInputStream on file, possibly decompressing gzip

Throws:

IOException - if there's an error opening the URL

makeImage

private NetpbmImage makeImage(InputStream input,
                              NetpbmImageFactory.ExceptionHolder exceptionHolder)
                       throws IOException

Load an image given an input stream. Requires an input stream that supports mark/reset in order to check the image's magic number. If this method returns null or throws an IOException, the input stream is automatically closed. Otherwise, it is the responsibility of the NetpbmImage to close the input stream when all image data has been loaded.

Parameters:

input - an input stream that supports mark/reset

exceptionHolder - place to store the IOException that caused a null return value, if any.

Returns:

a NetpbmImage or null if the image magic number is not recognized, if there's an error reading the image header, or if the input stream is null

Throws:

IOException - if mark/reset is not supported; if there's an error reading the magic number; if the stream does not contain enough data to determine the magic number; if an error occurs while reseting the stream after reading the magic number.

readMagic

private String readMagic(InputStream input)
                  throws IOException

Reads the Netpbm magic number from the start of a file.

Parameters:

input - an input stream that supports mark/reset.

Returns:

the first two characters of the file, which may or may not be a valid Netpbm magic number.

Throws:

IOException - if there's an error reading the file or mark/reset is not supported

closeQuietly

private void closeQuietly(InputStream input)

Closes an input stream and silently discards IOExceptions encountered during closure.

Parameters:

input -