javax.imageio.IIOException: Not a JPEG file: starts with 0x47 0x49

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java处理图片时出现异常

javax.imageio.IIOException: Not a JPEG file: starts with 0x47 0x49
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readImageHeader(Native Method)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readNativeHeader(Unknown Source)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.checkTablesOnly(Unknown Source)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.gotoImage(Unknown Source)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readHeader(Unknown Source)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.getWidth(Unknown Source)
at com.test.filedownloader.ImageHandler.getImageDim(ImageHandler.java:60)
at com.test.filedownloader.ImageHandler.main(ImageHandler.java:96)
Exception in thread "main" java.lang.NullPointerException
at com.test.filedownloader.ImageHandler.getImageDim(ImageHandler.java:70)
at com.test.filedownloader.ImageHandler.main(ImageHandler.java:96)

出现这种错误是因为将gif 图片后缀改成了jpg

解决办法：

根据文件的前面几个字节，判断文件类型

private String getFileSuffix(final String path) throws IOException {String result = "";String hex="";if (path != null) {File image=new File(path);InputStream is = new FileInputStream(image);byte[] bt = new byte[2];  is.read(bt); MyLog.logger.info(bt+"\n"+bytesToHexString(bt));  hex=bytesToHexString(bt);is.close();if(hex.equals("ffd8")){result="jpg";}else if(hex.equals("4749")){result="gif";}else if(hex.equals("8950")){result="png";}}return result;}

public static String bytesToHexString(byte[] src) {          StringBuilder stringBuilder = new StringBuilder();          if (src == null || src.length <= 0) {              return null;          }          for (int i = 0; i < src.length; i++) {            int v = src[i] & 0xFF;              String hv = Integer.toHexString(v);              if (hv.length() < 2) {                  stringBuilder.append(0);              }              stringBuilder.append(hv);          }          return stringBuilder.toString();      }

调用的话就

String suffix = getFileSuffix(path);

一个png文件十六进制内容

可参看链接

http://www.acgist.com/article/134.html

http://blog.csdn.net/fenglibing/article/details/7728275

http://www.cnblogs.com/Wendy_Yu/archive/2011/12/27/2303118.html

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