代碼如下：

import java.util.HashMap; public class FileTypeUtils { public static final String IMAGE_JPEG = "image/jpeg";public static final String IMAGE_PNG = "image/png";public static final String IMAGE_GIF = "image/gif";public static final String IMAGE_BMP = "image/bmp";  PRivate static final HashMap<String, String> mFileTypes = new HashMap<String, String>();static {mFileTypes.put("FFD8FF", IMAGE_JPEG);mFileTypes.put("89504E47", IMAGE_PNG);mFileTypes.put("47494638", IMAGE_GIF);mFileTypes.put("424D", IMAGE_BMP);mFileTypes.put("25504446", "application/pdf");} /*** 獲取圖片格式*/    public static String getImgContentType(byte[] src) {StringBuilder builder = new StringBuilder();if (src == null || src.length <= 0) {return null;}String contentType;String hv;for (int i = 0; i < 4 && i < src.length; i++) {// 以十六進制（基數 16）無符號整數形式返回一個整數參數的字符串表示形式，并轉換為大寫hv = Integer.toHexString(src[i] & 0xFF).toUpperCase();if (hv.length() < 2) {builder.append(0);}builder.append(hv);contentType = mFileTypes.get(builder.toString());if(contentType!=null){return contentType;}}contentType = "image/jpeg";return contentType;} }