tim/prune/jpeg/drew/JpegSegmentReader.java

   1 package tim.prune.jpeg.drew;\r
   2 \r
   3 import java.io.*;\r
   4 \r
   5 /**\r
   6  * Class to perform read functions of Jpeg files, returning specific file segments\r
   7  * Based on Drew Noakes' Metadata extractor at http://drewnoakes.com\r
   8  */\r
   9 public class JpegSegmentReader\r
  10 {\r
  11         /** Start of scan marker */\r
  12         private static final byte SEGMENT_SOS = (byte)0xDA;\r
  13 \r
  14         /** End of image marker */\r
  15         private static final byte MARKER_EOI = (byte)0xD9;\r
  16 \r
  17         /** APP1 Jpeg segment identifier -- where Exif data is kept. */\r
  18         private static final byte SEGMENT_APP1 = (byte)0xE1;\r
  19 \r
  20         /** Magic numbers to mark the beginning of all Jpegs */\r
  21         private static final int MAGIC_JPEG_BYTE_1 = 0xFF;\r
  22         private static final int MAGIC_JPEG_BYTE_2 = 0xD8;\r
  23 \r
  24 \r
  25         /**\r
  26          * Get the Exif data segment for the specified file\r
  27          * @param inFile File to read\r
  28          * @return Exif data segment as byte array\r
  29          * @throws JpegException on file read errors or exif data errors\r
  30          */\r
  31         public static byte[] readExifSegment(File inFile) throws JpegException\r
  32         {\r
  33                 JpegSegmentData data = readSegments(inFile);\r
  34                 return data.getSegment(SEGMENT_APP1);\r
  35         }\r
  36 \r
  37 \r
  38         /**\r
  39          * Obtain the Jpeg segment data from the specified file\r
  40          * @param inFile File to read\r
  41          * @return Jpeg segment data from file\r
  42          * @throws JpegException on file read errors or exif data errors\r
  43          */\r
  44         private static JpegSegmentData readSegments(File inFile) throws JpegException\r
  45         {\r
  46                 JpegSegmentData segmentData = new JpegSegmentData();\r
  47                 BufferedInputStream bStream = null;\r
  48 \r
  49                 try\r
  50                 {\r
  51                         bStream = new BufferedInputStream(new FileInputStream(inFile));\r
  52                         // first two bytes should be jpeg magic number\r
  53                         final int magic1 = bStream.read() & 0xFF;\r
  54                         final int magic2 = bStream.read() & 0xFF;\r
  55                         if (magic1 != MAGIC_JPEG_BYTE_1 || magic2 != MAGIC_JPEG_BYTE_2) {\r
  56                                 throw new JpegException("not a jpeg file");\r
  57                         }\r
  58 \r
  59                         // Loop around segments found\r
  60                         boolean foundExif = false;\r
  61                         do\r
  62                         {\r
  63                                 // next byte is 0xFF\r
  64                                 byte segmentIdentifier = (byte) (bStream.read() & 0xFF);\r
  65                                 if ((segmentIdentifier & 0xFF) != 0xFF)\r
  66                                 {\r
  67                                         throw new JpegException("expected jpeg segment start 0xFF, not 0x"\r
  68                                                 + Integer.toHexString(segmentIdentifier & 0xFF));\r
  69                                 }\r
  70                                 // next byte is <segment-marker>\r
  71                                 byte thisSegmentMarker = (byte) (bStream.read() & 0xFF);\r
  72                                 // next 2-bytes are <segment-size>: [high-byte] [low-byte]\r
  73                                 byte[] segmentLengthBytes = new byte[2];\r
  74                                 bStream.read(segmentLengthBytes, 0, 2);\r
  75                                 int segmentLength = ((segmentLengthBytes[0] << 8) & 0xFF00) | (segmentLengthBytes[1] & 0xFF);\r
  76                                 // segment length includes size bytes, so subtract two\r
  77                                 segmentLength -= 2;\r
  78                                 if (segmentLength > bStream.available())\r
  79                                         throw new JpegException("segment size would extend beyond file stream length");\r
  80                                 else if (segmentLength < 0)\r
  81                                         throw new JpegException("segment size would be less than zero");\r
  82                                 byte[] segmentBytes = new byte[segmentLength];\r
  83                                 int bytesRead = bStream.read(segmentBytes, 0, segmentLength);\r
  84                                 // Bail if not all bytes read in one go - otherwise following sections will be out of step\r
  85                                 if (bytesRead != segmentLength) {\r
  86                                         throw new JpegException("Tried to read " + segmentLength + " bytes but only got " + bytesRead);\r
  87                                 }\r
  88                                 if ((thisSegmentMarker & 0xFF) == (SEGMENT_SOS & 0xFF))\r
  89                                 {\r
  90                                         // The 'Start-Of-Scan' segment comes last so break out of loop\r
  91                                         break;\r
  92                                 }\r
  93                                 else if ((thisSegmentMarker & 0xFF) == (MARKER_EOI & 0xFF))\r
  94                                 {\r
  95                                         // the 'End-Of-Image' segment - should already have exited by now\r
  96                                         break;\r
  97                                 }\r
  98                                 else\r
  99                                 {\r
 100                                         segmentData.addSegment(thisSegmentMarker, segmentBytes);\r
 101                                 }\r
 102                                 // loop through to the next segment if exif hasn't already been found\r
 103                                 foundExif = (thisSegmentMarker == SEGMENT_APP1);\r
 104                         }\r
 105                         while (!foundExif);\r
 106                 }\r
 107                 catch (FileNotFoundException fnfe)\r
 108                 {\r
 109                         throw new JpegException("Jpeg file not found");\r
 110                 }\r
 111                 catch (IOException ioe)\r
 112                 {\r
 113                         throw new JpegException("IOException processing Jpeg file: " + ioe.getMessage(), ioe);\r
 114                 }\r
 115                 finally\r
 116                 {\r
 117                         try\r
 118                         {\r
 119                                 if (bStream != null) {\r
 120                                         bStream.close();\r
 121                                 }\r
 122                         }\r
 123                         catch (IOException ioe) {\r
 124                                 throw new JpegException("IOException processing Jpeg file: " + ioe.getMessage(), ioe);\r
 125                         }\r
 126                 }\r
 127                 // Return the result\r
 128                 return segmentData;\r
 129         }\r
 130 }\r