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Gif读取之解决ArrayIndexOutOfBoundsException:4096读取gif文件

lifes77
 lifes77
发布于 2018/07/04 11:07
字数 4034
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昨天遇到个读取图片问题,在 ImageIO.read读取大部分图片时候没有问题,可是遇到个别的gif读取就报错了: ArrayIndexOutOfBoundsException

 

google一番,发现这是jdk6~8历史遗留问题。。。。。。差点翻车了

个别的gif很顽强!

附上链接:https://blog.csdn.net/clive_hua/article/details/77610591 ,                         https://www.jianshu.com/p/18888311fc9e

------------------------------------------华丽的解决分界线------------------------------------

成功读取了gif,嘿嘿。

附上解决代码:

 

/**
 * 从博客中获取用于微信分享的图片链接:大小要求300x300
 * @param htmlContent
 * @param id  博客ID
 * @return
 */
public static String getImageForWechatShare(String htmlContent, long id) {
    String originImageUrl = "https://static.oschina.net/uploads/space/2017/0606/104418_CPLl_2733728.png";
    if (StringUtils.isNotBlank(htmlContent)) {
        Document document = Jsoup.parse(htmlContent);
        Elements elements = document.select("img[src~=(?i)\\.(gif|png|bmp|svg|jpe?g)]");
        if (null == elements) {
            return originImageUrl;
        }
        if(elements.size() == 0) {
            return originImageUrl;
        }
        try {
            for(int i = 0; i < elements.size(); i++) {
                String imageUrl = elements.get(i).attr("src");
                if(GIF.equalsIgnoreCase(ImageUtils.getSuffix(imageUrl))){
                    return readGif(originImageUrl,imageUrl,id);
                }
                HttpClient httpClient = HttpClients.createDefault();
                RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(1000).setConnectionRequestTimeout(1000).setSocketTimeout(1000).build();
                HttpGet httpGet = new HttpGet(imageUrl);
                httpGet.setConfig(requestConfig);
                HttpResponse response = httpClient.execute(httpGet);
                BufferedImage image = ImageIO.read(response.getEntity().getContent());
                if (image.getWidth() > 300 && image.getHeight() > 300) {
                    CacheMgr.set(Blog.CACHE_BLOGS_FIRST_IMAGE,String.valueOf(id),imageUrl);
                    return imageUrl;
                }else{
                    return uploadToUp(originImageUrl,imageUrl,id);
                }
            }
        } catch (Exception e) {
            return originImageUrl;
        }

    }
    return originImageUrl;
}

/**
 * 读取gif
 *
 * @param originImageUrl  osc 300*300 LOGO
 * @param imageUrl        博客第一张图片
 * @param id              博客ID
 * @return
 */
public static String readGif(String originImageUrl,String imageUrl,long id) {
    GifDecoder.GifImage gif = null;
    try {
        gif = GifDecoder.read(getImageFromNetByUrl(imageUrl));
        System.out.println(String.format("gif url:%s,width:%d,height:%d",imageUrl,gif.getWidth(),gif.getHeight()));
    } catch (IOException e) {
        return originImageUrl;
    }
    if (gif.getWidth() > 300 && gif.getHeight() > 300) {
         CacheMgr.set(Blog.CACHE_BLOGS_FIRST_IMAGE,String.valueOf(id),imageUrl);
         return imageUrl;
     }else{
         return uploadToUp(originImageUrl,imageUrl,id);
     }
}

/**
 * 上传图片至又拍云
 *
 * @param originImageUrl  osc 300*300 LOGO
 * @param imageUrl        博客第一张图片
 * @param id              博客ID
 * @return
 */
public static String uploadToUp(String originImageUrl,String imageUrl,long id){
    try {
        imageUrl = ImageUtils.ME.upload("wx-share-blog.jpg", getImageFromNetByUrl(imageUrl));
    } catch (Exception e) {
       return originImageUrl;
    }
    imageUrl += "!/both/300x300";
    CacheMgr.set(Blog.CACHE_BLOGS_FIRST_IMAGE,String.valueOf(id),imageUrl);
    return imageUrl;
}


/**
 * 根据地址获得数据的字节流
 * @param strUrl 网络连接地址
 * @return
 */
public static byte[] getImageFromNetByUrl(String strUrl){
    try {
        URL url = new URL(strUrl);
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5 * 1000);
        InputStream inStream = conn.getInputStream();
        byte[] btImg = readInputStream(inStream);
        return btImg;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

/**
 * 从输入流中获取数据
 * @param inStream 输入流
 * @return
 * @throws Exception
 */
public static byte[] readInputStream(InputStream inStream) throws Exception{
    ByteArrayOutputStream outStream = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int len = 0;
    while( (len=inStream.read(buffer)) != -1 ){
        outStream.write(buffer, 0, len);
    }
    inStream.close();
    return outStream.toByteArray();

}

获取图片后缀:

public static String getSuffix(String name) {
   Pattern pat = Pattern.compile("[\\w]+[\\.](" + SUFFIXES + ")");// 正则判断
   Matcher mc = pat.matcher(name.toLowerCase());// 条件匹配
   String fileName = null;
   while (mc.find()) {
      fileName = mc.group();// 截取文件名后缀名
   }
   if (fileName != null) {
      return fileName.substring(fileName.lastIndexOf(".") + 1);
   }
   return null;
}

GifDecoder.java代码:

import static java.lang.System.arraycopy;

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

/*
 * Copyright 2014 Dhyan Blum
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/**
 * <p>
 * A decoder capable of processing a GIF data stream to render the graphics
 * contained in it. This implementation follows the official
 * <A HREF="http://www.w3.org/Graphics/GIF/spec-gif89a.txt">GIF
 * specification</A>.
 * </p>
 *
 * <p>
 * Example usage:
 * </p>
 *
 * <p>
 *
 * <pre>
 * final GifImage gifImage = GifDecoder.read(int[] data);
 * final int width = gifImage.getWidth();
 * final int height = gifImage.getHeight();
 * final int frameCount = gifImage.getFrameCount();
 * for (int i = 0; i < frameCount; i++) {
 *     final BufferedImage image = gifImage.getFrame(i);
 *     final int delay = gif.getDelay(i);
 * }
 * </pre>
 *
 * </p>
 *
 * @author Dhyan Blum
 * @version 1.09 November 2017
 *
 */
public final class GifDecoder {
   static final class BitReader {
      private int bitPos; // Next bit to read
      private int numBits; // Number of bits to read
      private int bitMask; // Use to kill unwanted higher bits
      private byte[] in; // Data array

      // To avoid costly bounds checks, 'in' needs 2 more 0-bytes at the end
      private final void init(final byte[] in) {
         this.in = in;
         bitPos = 0;
      }

      private final int read() {
         // Byte indices: (bitPos / 8), (bitPos / 8) + 1, (bitPos / 8) + 2
         int i = bitPos >>> 3; // Byte = bit / 8
         // Bits we'll shift to the right, AND 7 is the same as MODULO 8
         final int rBits = bitPos & 7;
         // Byte 0 to 2, AND to get their unsigned values
         final int b0 = in[i++] & 0xFF, b1 = in[i++] & 0xFF, b2 = in[i] & 0xFF;
         // Glue the bytes together, don't do more shifting than necessary
         final int buf = ((b2 << 8 | b1) << 8 | b0) >>> rBits;
         bitPos += numBits;
         return buf & bitMask; // Kill the unwanted higher bits
      }

      private final void setNumBits(final int numBits) {
         this.numBits = numBits;
         bitMask = (1 << numBits) - 1;
      }
   }

   static final class CodeTable {
      private final int[][] tbl; // Maps codes to lists of colors
      private int initTableSize; // Number of colors +2 for CLEAR + EOI
      private int initCodeSize; // Initial code size
      private int initCodeLimit; // First code limit
      private int codeSize; // Current code size, maximum is 12 bits
      private int nextCode; // Next available code for a new entry
      private int nextCodeLimit; // Increase codeSize when nextCode == limit
      private BitReader br; // Notify when code sizes increases

      public CodeTable() {
         tbl = new int[4096][1];
      }

      private final int add(final int[] indices) {
         if (nextCode < 4096) {
            if (nextCode == nextCodeLimit && codeSize < 12) {
               codeSize++; // Max code size is 12
               br.setNumBits(codeSize);
               nextCodeLimit = (1 << codeSize) - 1; // 2^codeSize - 1
            }
            tbl[nextCode++] = indices;
         }
         return codeSize;
      }

      private final int clear() {
         codeSize = initCodeSize;
         br.setNumBits(codeSize);
         nextCodeLimit = initCodeLimit;
         nextCode = initTableSize; // Don't recreate table, reset pointer
         return codeSize;
      }

      private final void init(final GifFrame fr, final int[] activeColTbl, final BitReader br) {
         this.br = br;
         final int numColors = activeColTbl.length;
         initCodeSize = fr.firstCodeSize;
         initCodeLimit = (1 << initCodeSize) - 1; // 2^initCodeSize - 1
         initTableSize = fr.endOfInfoCode + 1;
         nextCode = initTableSize;
         for (int c = numColors - 1; c >= 0; c--) {
            tbl[c][0] = activeColTbl[c]; // Translated color
         } // A gap may follow with no colors assigned if numCols < CLEAR
         tbl[fr.clearCode] = new int[] { fr.clearCode }; // CLEAR
         tbl[fr.endOfInfoCode] = new int[] { fr.endOfInfoCode }; // EOI
         // Locate transparent color in code table and set to 0
         if (fr.transpColFlag && fr.transpColIndex < numColors) {
            tbl[fr.transpColIndex][0] = 0;
         }
      }
   }

   final class GifFrame {
      // Graphic control extension (optional)
      // Disposal: 0=NO_ACTION, 1=NO_DISPOSAL, 2=RESTORE_BG, 3=RESTORE_PREV
      private int disposalMethod; // 0-3 as above, 4-7 undefined
      private boolean transpColFlag; // 1 Bit
      private int delay; // Unsigned, LSByte first, n * 1/100 * s
      private int transpColIndex; // 1 Byte
      // Image descriptor
      private int x; // Position on the canvas from the left
      private int y; // Position on the canvas from the top
      private int w; // May be smaller than the base image
      private int h; // May be smaller than the base image
      private int wh; // width * height
      private boolean hasLocColTbl; // Has local color table? 1 Bit
      private boolean interlaceFlag; // Is an interlace image? 1 Bit
      @SuppressWarnings("unused")
      private boolean sortFlag; // True if local colors are sorted, 1 Bit
      private int sizeOfLocColTbl; // Size of the local color table, 3 Bits
      private int[] localColTbl; // Local color table (optional)
      // Image data
      private int firstCodeSize; // LZW minimum code size + 1 for CLEAR & EOI
      private int clearCode;
      private int endOfInfoCode;
      private byte[] data; // Holds LZW encoded data
      private BufferedImage img; // Full drawn image, not just the frame area
   }

   public final class GifImage {
      public String header; // Bytes 0-5, GIF87a or GIF89a
      private int w; // Unsigned 16 Bit, least significant byte first
      private int h; // Unsigned 16 Bit, least significant byte first
      private int wh; // Image width * image height
      public boolean hasGlobColTbl; // 1 Bit
      public int colorResolution; // 3 Bits
      public boolean sortFlag; // True if global colors are sorted, 1 Bit
      public int sizeOfGlobColTbl; // 2^(val(3 Bits) + 1), see spec
      public int bgColIndex; // Background color index, 1 Byte
      public int pxAspectRatio; // Pixel aspect ratio, 1 Byte
      public int[] globalColTbl; // Global color table
      private final List<GifFrame> frames = new ArrayList<GifFrame>(64);
      public String appId = ""; // 8 Bytes at in[i+3], usually "NETSCAPE"
      public String appAuthCode = ""; // 3 Bytes at in[i+11], usually "2.0"
      public int repetitions = 0; // 0: infinite loop, N: number of loops
      private BufferedImage img = null; // Currently drawn frame
      private int[] prevPx = null; // Previous frame's pixels
      private final BitReader bits = new BitReader();
      private final CodeTable codes = new CodeTable();
      private Graphics2D g;

      private final int[] decode(final GifFrame fr, final int[] activeColTbl) {
         codes.init(fr, activeColTbl, bits);
         bits.init(fr.data); // Incoming codes
         final int clearCode = fr.clearCode, endCode = fr.endOfInfoCode;
         final int[] out = new int[wh]; // Target image pixel array
         final int[][] tbl = codes.tbl; // Code table
         int outPos = 0; // Next pixel position in the output image array
         codes.clear(); // Init code table
         bits.read(); // Skip leading clear code
         int code = bits.read(); // Read first code
         int[] pixels = tbl[code]; // Output pixel for first code
         arraycopy(pixels, 0, out, outPos, pixels.length);
         outPos += pixels.length;
         try {
            while (true) {
               final int prevCode = code;
               code = bits.read(); // Get next code in stream
               if (code == clearCode) { // After a CLEAR table, there is
                  codes.clear(); // no previous code, we need to read
                  code = bits.read(); // a new one
                  pixels = tbl[code]; // Output pixels
                  arraycopy(pixels, 0, out, outPos, pixels.length);
                  outPos += pixels.length;
                  continue; // Back to the loop with a valid previous code
               } else if (code == endCode) {
                  break;
               }
               final int[] prevVals = tbl[prevCode];
               final int[] prevValsAndK = new int[prevVals.length + 1];
               arraycopy(prevVals, 0, prevValsAndK, 0, prevVals.length);
               if (code < codes.nextCode) { // Code table contains code
                  pixels = tbl[code]; // Output pixels
                  arraycopy(pixels, 0, out, outPos, pixels.length);
                  outPos += pixels.length;
                  prevValsAndK[prevVals.length] = tbl[code][0]; // K
               } else {
                  prevValsAndK[prevVals.length] = prevVals[0]; // K
                  arraycopy(prevValsAndK, 0, out, outPos, prevValsAndK.length);
                  outPos += prevValsAndK.length;
               }
               codes.add(prevValsAndK); // Previous indices + K
            }
         } catch (final ArrayIndexOutOfBoundsException e) {
         }
         return out;
      }

      private final int[] deinterlace(final int[] src, final GifFrame fr) {
         final int w = fr.w, h = fr.h, wh = fr.wh;
         final int[] dest = new int[src.length];
         // Interlaced images are organized in 4 sets of pixel lines
         final int set2Y = (h + 7) >>> 3; // Line no. = ceil(h/8.0)
         final int set3Y = set2Y + ((h + 3) >>> 3); // ceil(h-4/8.0)
         final int set4Y = set3Y + ((h + 1) >>> 2); // ceil(h-2/4.0)
         // Sets' start indices in source array
         final int set2 = w * set2Y, set3 = w * set3Y, set4 = w * set4Y;
         // Line skips in destination array
         final int w2 = w << 1, w4 = w2 << 1, w8 = w4 << 1;
         // Group 1 contains every 8th line starting from 0
         int from = 0, to = 0;
         for (; from < set2; from += w, to += w8) {
            arraycopy(src, from, dest, to, w);
         } // Group 2 contains every 8th line starting from 4
         for (to = w4; from < set3; from += w, to += w8) {
            arraycopy(src, from, dest, to, w);
         } // Group 3 contains every 4th line starting from 2
         for (to = w2; from < set4; from += w, to += w4) {
            arraycopy(src, from, dest, to, w);
         } // Group 4 contains every 2nd line starting from 1 (biggest group)
         for (to = w; from < wh; from += w, to += w2) {
            arraycopy(src, from, dest, to, w);
         }
         return dest; // All pixel lines have now been rearranged
      }

      private final void drawFrame(final GifFrame fr) {
         // Determine the color table that will be active for this frame
         final int[] activeColTbl = fr.hasLocColTbl ? fr.localColTbl : globalColTbl;
         // Get pixels from data stream
         int[] pixels = decode(fr, activeColTbl);
         if (fr.interlaceFlag) {
            pixels = deinterlace(pixels, fr); // Rearrange pixel lines
         }
         // Create image of type 2=ARGB for frame area
         final BufferedImage frame = new BufferedImage(fr.w, fr.h, 2);
         arraycopy(pixels, 0, ((DataBufferInt) frame.getRaster().getDataBuffer()).getData(), 0, fr.wh);
         // Draw frame area on top of working image
         g.drawImage(frame, fr.x, fr.y, null);

         // Visualize frame boundaries during testing
         // if (DEBUG_MODE) {
         // if (prev != null) {
         // g.setColor(Color.RED); // Previous frame color
         // g.drawRect(prev.x, prev.y, prev.w - 1, prev.h - 1);
         // }
         // g.setColor(Color.GREEN); // New frame color
         // g.drawRect(fr.x, fr.y, fr.w - 1, fr.h - 1);
         // }

         // Keep one copy as "previous frame" in case we need to restore it
         prevPx = new int[wh];
         arraycopy(((DataBufferInt) img.getRaster().getDataBuffer()).getData(), 0, prevPx, 0, wh);

         // Create another copy for the end user to not expose internal state
         fr.img = new BufferedImage(w, h, 2); // 2 = ARGB
         arraycopy(prevPx, 0, ((DataBufferInt) fr.img.getRaster().getDataBuffer()).getData(), 0, wh);

         // Handle disposal of current frame
         if (fr.disposalMethod == 2) {
            // Restore to background color (clear frame area only)
            g.clearRect(fr.x, fr.y, fr.w, fr.h);
         } else if (fr.disposalMethod == 3 && prevPx != null) {
            // Restore previous frame
            arraycopy(prevPx, 0, ((DataBufferInt) img.getRaster().getDataBuffer()).getData(), 0, wh);
         }
      }

      /**
       * Returns the background color of the first frame in this GIF image. If
       * the frame has a local color table, the returned color will be from
       * that table. If not, the color will be from the global color table.
       * Returns 0 if there is neither a local nor a global color table.
       *
       * @param index
       *            Index of the current frame, 0 to N-1
       * @return 32 bit ARGB color in the form 0xAARRGGBB
       */
      public final int getBackgroundColor() {
         final GifFrame frame = frames.get(0);
         if (frame.hasLocColTbl) {
            return frame.localColTbl[bgColIndex];
         } else if (hasGlobColTbl) {
            return globalColTbl[bgColIndex];
         }
         return 0;
      }

      /**
       * If not 0, the delay specifies how many hundredths (1/100) of a second
       * to wait before displaying the frame <i>after</i> the current frame.
       *
       * @param index
       *            Index of the current frame, 0 to N-1
       * @return Delay as number of hundredths (1/100) of a second
       */
      public final int getDelay(final int index) {
         return frames.get(index).delay;
      }

      /**
       * @param index
       *            Index of the frame to return as image, starting from 0.
       *            For incremental calls such as [0, 1, 2, ...] the method's
       *            run time is O(1) as only one frame is drawn per call. For
       *            random access calls such as [7, 12, ...] the run time is
       *            O(N+1) with N being the number of previous frames that
       *            need to be drawn before N+1 can be drawn on top. Once a
       *            frame has been drawn it is being cached and the run time
       *            is more or less O(0) to retrieve it from the list.
       * @return A BufferedImage for the specified frame.
       */
      public final BufferedImage getFrame(final int index) {
         if (img == null) { // Init
            img = new BufferedImage(w, h, 2); // 2 = ARGB
            g = img.createGraphics();
            g.setBackground(new Color(0, true)); // Transparent color
         }
         GifFrame fr = frames.get(index);
         if (fr.img == null) {
            // Draw all frames until and including the requested frame
            for (int i = 0; i <= index; i++) {
               fr = frames.get(i);
               if (fr.img == null) {
                  drawFrame(fr);
               }
            }
         }
         return fr.img;
      }

      /**
       * @return The number of frames contained in this GIF image
       */
      public final int getFrameCount() {
         return frames.size();
      }

      /**
       * @return The height of the GIF image
       */
      public final int getHeight() {
         return h;
      }

      /**
       * @return The width of the GIF image
       */
      public final int getWidth() {
         return w;
      }
   }

   static final boolean DEBUG_MODE = false;

   /**
    * @param in
    *            Raw image data as a byte[] array
    * @return A GifImage object exposing the properties of the GIF image.
    * @throws IOException
    *             If the image violates the GIF specification or is truncated.
    */
   public static final GifImage read(final byte[] in) throws IOException {
      final GifDecoder decoder = new GifDecoder();
      final GifImage img = decoder.new GifImage();
      GifFrame frame = null; // Currently open frame
      int pos = readHeader(in, img); // Read header, get next byte position
      pos = readLogicalScreenDescriptor(img, in, pos);
      if (img.hasGlobColTbl) {
         img.globalColTbl = new int[img.sizeOfGlobColTbl];
         pos = readColTbl(in, img.globalColTbl, pos);
      }
      while (pos < in.length) {
         final int block = in[pos] & 0xFF;
         switch (block) {
         case 0x21: // Extension introducer
            if (pos + 1 >= in.length) {
               throw new IOException("Unexpected end of file.");
            }
            switch (in[pos + 1] & 0xFF) {
            case 0xFE: // Comment extension
               pos = readTextExtension(in, pos);
               break;
            case 0xFF: // Application extension
               pos = readAppExt(img, in, pos);
               break;
            case 0x01: // Plain text extension
               frame = null; // End of current frame
               pos = readTextExtension(in, pos);
               break;
            case 0xF9: // Graphic control extension
               if (frame == null) {
                  frame = decoder.new GifFrame();
                  img.frames.add(frame);
               }
               pos = readGraphicControlExt(frame, in, pos);
               break;
            default:
               throw new IOException("Unknown extension at " + pos);
            }
            break;
         case 0x2C: // Image descriptor
            if (frame == null) {
               frame = decoder.new GifFrame();
               img.frames.add(frame);
            }
            pos = readImgDescr(frame, in, pos);
            if (frame.hasLocColTbl) {
               frame.localColTbl = new int[frame.sizeOfLocColTbl];
               pos = readColTbl(in, frame.localColTbl, pos);
            }
            pos = readImgData(frame, in, pos);
            frame = null; // End of current frame
            break;
         case 0x3B: // GIF Trailer
            return img; // Found trailer, finished reading.
         default:
            // Unknown block. The image is corrupted. Strategies: a) Skip
            // and wait for a valid block. Experience: It'll get worse. b)
            // Throw exception. c) Return gracefully if we are almost done
            // processing. The frames we have so far should be error-free.
            final double progress = 1.0 * pos / in.length;
            if (progress < 0.9) {
               throw new IOException("Unknown block at: " + pos);
            }
            pos = in.length; // Exit loop
         }
      }
      return img;
   }

   /**
    * @param is
    *            Image data as input stream. This method will read from the
    *            input stream's current position. It will not reset the
    *            position before reading and won't reset or close the stream
    *            afterwards. Call these methods before and after calling this
    *            method as needed.
    * @return A GifImage object exposing the properties of the GIF image.
    * @throws IOException
    *             If an I/O error occurs, the image violates the GIF
    *             specification or the GIF is truncated.
    */
   public static final GifImage read(final InputStream is) throws IOException {
      final byte[] data = new byte[is.available()];
      is.read(data, 0, data.length);
      return read(data);
   }

   /**
    * @param ext
    *            Empty application extension object
    * @param in
    *            Raw data
    * @param i
    *            Index of the first byte of the application extension
    * @return Index of the first byte after this extension
    */
   static final int readAppExt(final GifImage img, final byte[] in, int i) {
      img.appId = new String(in, i + 3, 8); // should be "NETSCAPE"
      img.appAuthCode = new String(in, i + 11, 3); // should be "2.0"
      i += 14; // Go to sub-block size, it's value should be 3
      final int subBlockSize = in[i] & 0xFF;
      // The only app extension widely used is NETSCAPE, it's got 3 data bytes
      if (subBlockSize == 3) {
         // in[i+1] should have value 01, in[i+5] should be block terminator
         img.repetitions = in[i + 2] & 0xFF | in[i + 3] & 0xFF << 8; // Short
         return i + 5;
      } // Skip unknown application extensions
      while ((in[i] & 0xFF) != 0) { // While sub-block size != 0
         i += (in[i] & 0xFF) + 1; // Skip to next sub-block
      }
      return i + 1;
   }

   /**
    * @param in
    *            Raw data
    * @param colors
    *            Pre-initialized target array to store ARGB colors
    * @param i
    *            Index of the color table's first byte
    * @return Index of the first byte after the color table
    */
   static final int readColTbl(final byte[] in, final int[] colors, int i) {
      final int numColors = colors.length;
      for (int c = 0; c < numColors; c++) {
         final int a = 0xFF; // Alpha 255 (opaque)
         final int r = in[i++] & 0xFF; // 1st byte is red
         final int g = in[i++] & 0xFF; // 2nd byte is green
         final int b = in[i++] & 0xFF; // 3rd byte is blue
         colors[c] = ((a << 8 | r) << 8 | g) << 8 | b;
      }
      return i;
   }

   /**
    * @param ext
    *            Graphic control extension object
    * @param in
    *            Raw data
    * @param i
    *            Index of the extension introducer
    * @return Index of the first byte after this block
    */
   static final int readGraphicControlExt(final GifFrame fr, final byte[] in, final int i) {
      fr.disposalMethod = (in[i + 3] & 0b00011100) >>> 2; // Bits 4-2
      fr.transpColFlag = (in[i + 3] & 1) == 1; // Bit 0
      fr.delay = in[i + 4] & 0xFF | (in[i + 5] & 0xFF) << 8; // 16 bit LSB
      fr.transpColIndex = in[i + 6] & 0xFF; // Byte 6
      return i + 8; // Skipped byte 7 (blockTerminator), as it's always 0x00
   }

   /**
    * @param in
    *            Raw data
    * @param img
    *            The GifImage object that is currently read
    * @return Index of the first byte after this block
    * @throws IOException
    *             If the GIF header/trailer is missing, incomplete or unknown
    */
   static final int readHeader(final byte[] in, final GifImage img) throws IOException {
      if (in.length < 6) { // Check first 6 bytes
         throw new IOException("Image is truncated.");
      }
      img.header = new String(in, 0, 6);
      if (!img.header.equals("GIF87a") && !img.header.equals("GIF89a")) {
         throw new IOException("Invalid GIF header.");
      }
      return 6;
   }

   /**
    * @param fr
    *            The GIF frame to whom this image descriptor belongs
    * @param in
    *            Raw data
    * @param i
    *            Index of the first byte of this block, i.e. the minCodeSize
    * @return
    */
   static final int readImgData(final GifFrame fr, final byte[] in, int i) {
      final int fileSize = in.length;
      final int minCodeSize = in[i++] & 0xFF; // Read code size, go to block
      final int clearCode = 1 << minCodeSize; // CLEAR = 2^minCodeSize
      fr.firstCodeSize = minCodeSize + 1; // Add 1 bit for CLEAR and EOI
      fr.clearCode = clearCode;
      fr.endOfInfoCode = clearCode + 1;
      final int imgDataSize = readImgDataSize(in, i);
      final byte[] imgData = new byte[imgDataSize + 2];
      int imgDataPos = 0;
      int subBlockSize = in[i] & 0xFF;
      while (subBlockSize > 0) { // While block has data
         try { // Next line may throw exception if sub-block size is fake
            final int nextSubBlockSizePos = i + subBlockSize + 1;
            final int nextSubBlockSize = in[nextSubBlockSizePos] & 0xFF;
            arraycopy(in, i + 1, imgData, imgDataPos, subBlockSize);
            imgDataPos += subBlockSize; // Move output data position
            i = nextSubBlockSizePos; // Move to next sub-block size
            subBlockSize = nextSubBlockSize;
         } catch (final Exception e) {
            // Sub-block exceeds file end, only use remaining bytes
            subBlockSize = fileSize - i - 1; // Remaining bytes
            arraycopy(in, i + 1, imgData, imgDataPos, subBlockSize);
            imgDataPos += subBlockSize; // Move output data position
            i += subBlockSize + 1; // Move to next sub-block size
            break;
         }
      }
      fr.data = imgData; // Holds LZW encoded data
      i++; // Skip last sub-block size, should be 0
      return i;
   }

   static final int readImgDataSize(final byte[] in, int i) {
      final int fileSize = in.length;
      int imgDataPos = 0;
      int subBlockSize = in[i] & 0xFF;
      while (subBlockSize > 0) { // While block has data
         try { // Next line may throw exception if sub-block size is fake
            final int nextSubBlockSizePos = i + subBlockSize + 1;
            final int nextSubBlockSize = in[nextSubBlockSizePos] & 0xFF;
            imgDataPos += subBlockSize; // Move output data position
            i = nextSubBlockSizePos; // Move to next sub-block size
            subBlockSize = nextSubBlockSize;
         } catch (final Exception e) {
            // Sub-block exceeds file end, only use remaining bytes
            subBlockSize = fileSize - i - 1; // Remaining bytes
            imgDataPos += subBlockSize; // Move output data position
            break;
         }
      }
      return imgDataPos;
   }

   /**
    * @param fr
    *            The GIF frame to whom this image descriptor belongs
    * @param in
    *            Raw data
    * @param i
    *            Index of the image separator, i.e. the first block byte
    * @return Index of the first byte after this block
    */
   static final int readImgDescr(final GifFrame fr, final byte[] in, int i) {
      fr.x = in[++i] & 0xFF | (in[++i] & 0xFF) << 8; // Byte 1-2: left
      fr.y = in[++i] & 0xFF | (in[++i] & 0xFF) << 8; // Byte 3-4: top
      fr.w = in[++i] & 0xFF | (in[++i] & 0xFF) << 8; // Byte 5-6: width
      fr.h = in[++i] & 0xFF | (in[++i] & 0xFF) << 8; // Byte 7-8: height
      fr.wh = fr.w * fr.h;
      final byte b = in[++i]; // Byte 9 is a packed byte
      fr.hasLocColTbl = (b & 0b10000000) >>> 7 == 1; // Bit 7
      fr.interlaceFlag = (b & 0b01000000) >>> 6 == 1; // Bit 6
      fr.sortFlag = (b & 0b00100000) >>> 5 == 1; // Bit 5
      final int colTblSizePower = (b & 7) + 1; // Bits 2-0
      fr.sizeOfLocColTbl = 1 << colTblSizePower; // 2^(N+1), As per the spec
      return ++i;
   }

   /**
    * @param img
    * @param i
    *            Start index of this block.
    * @return Index of the first byte after this block.
    */
   static final int readLogicalScreenDescriptor(final GifImage img, final byte[] in, final int i) {
      img.w = in[i] & 0xFF | (in[i + 1] & 0xFF) << 8; // 16 bit, LSB 1st
      img.h = in[i + 2] & 0xFF | (in[i + 3] & 0xFF) << 8; // 16 bit
      img.wh = img.w * img.h;
      final byte b = in[i + 4]; // Byte 4 is a packed byte
      img.hasGlobColTbl = (b & 0b10000000) >>> 7 == 1; // Bit 7
      final int colResPower = ((b & 0b01110000) >>> 4) + 1; // Bits 6-4
      img.colorResolution = 1 << colResPower; // 2^(N+1), As per the spec
      img.sortFlag = (b & 0b00001000) >>> 3 == 1; // Bit 3
      final int globColTblSizePower = (b & 7) + 1; // Bits 0-2
      img.sizeOfGlobColTbl = 1 << globColTblSizePower; // 2^(N+1), see spec
      img.bgColIndex = in[i + 5] & 0xFF; // 1 Byte
      img.pxAspectRatio = in[i + 6] & 0xFF; // 1 Byte
      return i + 7;
   }

   /**
    * @param in
    *            Raw data
    * @param pos
    *            Index of the extension introducer
    * @return Index of the first byte after this block
    */
   static final int readTextExtension(final byte[] in, final int pos) {
      int i = pos + 2; // Skip extension introducer and label
      int subBlockSize = in[i++] & 0xFF;
      while (subBlockSize != 0 && i < in.length) {
         i += subBlockSize;
         subBlockSize = in[i++] & 0xFF;
      }
      return i;
   }
}

                                                                                                                                                                                                                              -----ps:微信分享博客,需要300*300以上的图片。。。闹心

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