Android 中我们可以根据文件头的字符来确定文件类型

public class FileType {  
        public static final HashMap<String, String> mFileTypes = new HashMap<String, String>();
        static {
            //images
            mFileTypes.put("FFD8FF", "jpg");
            mFileTypes.put("89504E47", "png");
            mFileTypes.put("47494638", "gif");
            mFileTypes.put("49492A00", "tif");
            mFileTypes.put("424D", "bmp");
           
            mFileTypes.put("41433130", "dwg"); //CAD
            mFileTypes.put("38425053", "psd");
            mFileTypes.put("7B5C727466", "rtf"); //日记本
            mFileTypes.put("3C3F786D6C", "xml");
            mFileTypes.put("68746D6C3E", "html");
            mFileTypes.put("44656C69766572792D646174653A", "eml"); //邮件
            mFileTypes.put("D0CF11E0", "doc");
            mFileTypes.put("5374616E64617264204A", "mdb");
            mFileTypes.put("252150532D41646F6265", "ps");
            mFileTypes.put("255044462D312E", "pdf");
            mFileTypes.put("504B0304", "zip");
            mFileTypes.put("52617221", "rar");
            mFileTypes.put("57415645", "wav");
            mFileTypes.put("41564920", "avi");
            mFileTypes.put("2E524D46", "rm");
            mFileTypes.put("000001BA", "mpg");
            mFileTypes.put("000001B3", "mpg");
            mFileTypes.put("6D6F6F76", "mov");
            mFileTypes.put("3026B2758E66CF11", "asf");
            mFileTypes.put("4D546864", "mid");
            mFileTypes.put("1F8B08", "gz");
        }
            
        //获取文件类型
        public static String getFileType(String filePath) {
            return mFileTypes.get(getFileHeader(filePath));
        }
        //获取文件头信息
        public static String getFileHeader(String filePath) {
            FileInputStream is = null;
            String value = null;
            try {
                is = new FileInputStream(filePath);
                byte[] b = new byte[3];  
                is.read(b, 0, b.length);
                value = bytesToHexString(b);
            } catch (Exception e) {
            } finally {
                if(null != is) {
                    try {
                        is.close();
                    } catch (IOException e) {}
                }
            }
            return value;
        }
        private static String bytesToHexString(byte[] src){     
             StringBuilder builder = new StringBuilder();     
             if (src == null || src.length <= 0) {     
                 return null;     
             }
             String hv;
             for (int i = 0; i < src.length; i++) {     
                 hv = Integer.toHexString(src[i] & 0xFF).toUpperCase();     
                 if (hv.length() < 2) {     
                     builder.append(0);     
                 }     
                 builder.append(hv);
             }
             return builder.toString();     
         }  
        
}