Java 读取图片的mimeType的方法

if(filename.endsWith(".png") || filename.endsWith(".jpg"))
{
  //保存图片
}else{
  throw new IOException("Error file format ！");
}

private static boolean isBMP(byte[] buf){
 byte[] markBuf = "BM".getBytes(); //BMP图片文件的前两个字节
 return compare(buf, markBuf);
 }
 
 private static boolean isICON(byte[] buf) {
 byte[] markBuf = {0, 0, 1, 0, 1, 0, 32, 32};
 return compare(buf, markBuf);
 }
 private static boolean isWEBP(byte[] buf) {
 byte[] markBuf = "RIFF".getBytes(); //WebP图片识别符
 return compare(buf, markBuf);
 }

 private static boolean isGIF(byte[] buf) { 
 byte[] markBuf = "GIF89a".getBytes(); //GIF识别符
 if(compare(buf, markBuf))
 {
  return true;
 }
 markBuf = "GIF87a".getBytes(); //GIF识别符
 if(compare(buf, markBuf))
 {
  return true;
 }
 return false;
 }
 private static boolean isPNG(byte[] buf) { 
 byte[] markBuf = {(byte) 0x89,0x50,0x4E,0x47,0x0D,0x0A,0x1A,0x0A}; //PNG识别符
  // new String(buf).indexOf("PNG")>0 //也可以使用这种方式
 return compare(buf, markBuf);
 }

 private static boolean isJPEGHeader(byte[] buf) {
 byte[] markBuf = {(byte) 0xff, (byte) 0xd8}; //JPEG开始符 
 return compare(buf, markBuf);
 }
 
 private static boolean isJPEGFooter(byte[] buf)//JPEG结束符
 {
 byte[] markBuf = {(byte) 0xff, (byte) 0xd9}; 
 return compare(buf, markBuf);
 }

/**
 * 获取文件的mimeType
 * @param filename
 * @return
 */
 private static String getMimeType(String filename){
 try {
  String mimeType = readType(filename);
  return String.format("image/%s", mimeType);
 } catch (IOException e) {
  e.printStackTrace();
 }
 return null;
 }

 /**
 * 读取文件类型
 * @param filename
 * @return
 * @throws IOException
 */
 private static String readType(String filename) throws IOException {
 
 FileInputStream fis = null;
 try {
  File f = new File(filename);
  if(!f.exists() || f.isDirectory() || f.length()<8) {
  throw new IOException("the file ["+f.getAbsolutePath()+"] is not image !");
  }
  
  fis= new FileInputStream(f);
  byte[] bufHeaders = readInputStreamAt(fis,0,8);
  if(isJPEGHeader(bufHeaders))
  { 
  long skiplength = f.length()-2-8; //第一次读取时已经读了8个byte,因此需要减掉
  byte[] bufFooters = readInputStreamAt(fis, skiplength, 2);
  if(isJPEGFooter(bufFooters))
  {
   return "jpeg";
  }
  }
  if(isPNG(bufHeaders))
  {
  return "png";
  }
  if(isGIF(bufHeaders)){
  
  return "gif";
  }
  if(isWEBP(bufHeaders))
  {
  return "webp";
  }
  if(isBMP(bufHeaders))
  {
  return "bmp";
  }
  if(isICON(bufHeaders))
  {
  return "ico";
  }
  throw new IOException("the image's format is unkown!");
  
 } catch (FileNotFoundException e) {
  throw e;
 }finally{
  try {
  if(fis!=null) fis.close();
  } catch (Exception e) {
  }
 }
 
 }
 
 /**
 * 标示一致性比较
 * @param buf 待检测标示
 * @param markBuf 标识符字节数组
 * @return 返回false标示标示不匹配
 */
 private static boolean compare(byte[] buf, byte[] markBuf) {
 for (int i = 0; i < markBuf.length; i++) {
  byte b = markBuf[i];
  byte a = buf[i];
  
  if(a!=b){
  return false;
  }
 }
 return true;
 }
 /**
 * 
 * @param fis 输入流对象
 * @param skiplength 跳过位置长度
 * @param length 要读取的长度
 * @return 字节数组
 * @throws IOException
 */
 private static byte[] readInputStreamAt(FileInputStream fis, long skiplength, int length) throws IOException
 {
 byte[] buf = new byte[length];
 fis.skip(skiplength); //
 int read = fis.read(buf,0,length);
 return buf;
 }

public class ImageType {
 public static void main(String[] args) { 
  String filename = "oschina.jpg";
  String type = getMimeType(filename);
  System.out.println(type);
 }
}

public class ImageType {
 public static void main(String[] args) {
 
  String filename = "oschina.png";
  String type = getMimeType(filename);
  System.out.println(type);
 
  filename = "oschina";
  type = getMimeType(filename);
  System.out.println(type);
      
 }
}