Java处理图片时出现异常

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

/*
* 判断图片的原始类型 2016-6-27
*/
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);
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();
}