Java獲取文件類型/擴展名

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

public class FileTypeUtils {

   private final static Map<String, String> FILE_TYPE_MAP = new HashMap<>();

   private FileTypeUtils() {
   }

   static {
      getAllFileType(); //初始化文件類型信息
   }

   /**
    * 常見文件頭信息
    */
   private static void getAllFileType() {
      /*FILE_TYPE_MAP.put("ffd8ffe000104a464946", "jpg"); //JPEG (jpg)
      FILE_TYPE_MAP.put("89504e470d0a1a0a0000", "png"); //PNG (png)
      FILE_TYPE_MAP.put("47494638396126026f01", "gif"); //GIF (gif)
      FILE_TYPE_MAP.put("49492a00227105008037", "tif"); //TIFF (tif)
      FILE_TYPE_MAP.put("424d228c010000000000", "bmp"); //16色位圖(bmp)
      FILE_TYPE_MAP.put("424d8240090000000000", "bmp"); //24位位圖(bmp)
      FILE_TYPE_MAP.put("424d8e1b030000000000", "bmp"); //256色位圖(bmp)
      FILE_TYPE_MAP.put("41433130313500000000", "dwg"); //CAD (dwg)
      FILE_TYPE_MAP.put("3c21444f435459504520", "html"); //HTML (html)
      FILE_TYPE_MAP.put("3c21646f637479706520", "htm"); //HTM (htm)
      FILE_TYPE_MAP.put("48544d4c207b0d0a0942", "css"); //css
      FILE_TYPE_MAP.put("696b2e71623d696b2e71", "js"); //js
      FILE_TYPE_MAP.put("7b5c727466315c616e73", "rtf"); //Rich Text Format (rtf)
      FILE_TYPE_MAP.put("38425053000100000000", "psd"); //Photoshop (psd)
      FILE_TYPE_MAP.put("46726f6d3a203d3f6762", "eml"); //Email [Outlook Express 6] (eml)
      FILE_TYPE_MAP.put("d0cf11e0a1b11ae10000", "doc"); //MS Excel 注意：word、msi 和 excel的文件頭同樣
      FILE_TYPE_MAP.put("d0cf11e0a1b11ae10000", "vsd"); //Visio 繪圖
      FILE_TYPE_MAP.put("5374616E64617264204A", "mdb"); //MS Access (mdb)
      FILE_TYPE_MAP.put("252150532D41646F6265", "ps");
      FILE_TYPE_MAP.put("255044462d312e350d0a", "pdf"); //Adobe Acrobat (pdf)
      FILE_TYPE_MAP.put("2e524d46000000120001", "rmvb"); //rmvb/rm相同
      FILE_TYPE_MAP.put("464c5601050000000900", "flv"); //flv與f4v相同
      FILE_TYPE_MAP.put("00000020667479706d70", "mp4");
      FILE_TYPE_MAP.put("49443303000000002176", "mp3");
      FILE_TYPE_MAP.put("000001ba210001000180", "mpg"); //
      FILE_TYPE_MAP.put("3026b2758e66cf11a6d9", "wmv"); //wmv與asf相同
      FILE_TYPE_MAP.put("52494646e27807005741", "wav"); //Wave (wav)
      FILE_TYPE_MAP.put("52494646d07d60074156", "avi");
      FILE_TYPE_MAP.put("4d546864000000060001", "mid"); //MIDI (mid)
      FILE_TYPE_MAP.put("504b0304140000000800", "zip");
      FILE_TYPE_MAP.put("526172211a0700cf9073", "rar");
      FILE_TYPE_MAP.put("235468697320636f6e66", "ini");
      FILE_TYPE_MAP.put("504b03040a0000000000", "jar");
      FILE_TYPE_MAP.put("4d5a9000030000000400", "exe");//可執行文件
      FILE_TYPE_MAP.put("3c25402070616765206c", "jsp");//jsp文件
      FILE_TYPE_MAP.put("4d616e69666573742d56", "mf");//MF文件
      FILE_TYPE_MAP.put("3c3f786d6c2076657273", "xml");//xml文件
      FILE_TYPE_MAP.put("494e5345525420494e54", "sql");//xml文件
      FILE_TYPE_MAP.put("7061636b616765207765", "java");//java文件
      FILE_TYPE_MAP.put("406563686f206f66660d", "bat");//bat文件
      FILE_TYPE_MAP.put("1f8b0800000000000000", "gz");//gz文件
      FILE_TYPE_MAP.put("6c6f67346a2e726f6f74", "properties");//bat文件
      FILE_TYPE_MAP.put("cafebabe0000002e0041", "class");//bat文件
      FILE_TYPE_MAP.put("49545346030000006000", "chm");//bat文件
      FILE_TYPE_MAP.put("04000000010000001300", "mxp");//bat文件
      FILE_TYPE_MAP.put("504b0304140006000800", "docx");//docx文件
      FILE_TYPE_MAP.put("d0cf11e0a1b11ae10000", "wps");//WPS文字wps、表格et、演示dps都是同樣的
      FILE_TYPE_MAP.put("6431303a637265617465", "torrent");


      FILE_TYPE_MAP.put("6D6F6F76", "mov"); //Quicktime (mov)
      FILE_TYPE_MAP.put("FF575043", "wpd"); //WordPerfect (wpd)
      FILE_TYPE_MAP.put("CFAD12FEC5FD746F", "dbx"); //Outlook Express (dbx)
      FILE_TYPE_MAP.put("2142444E", "pst"); //Outlook (pst)
      FILE_TYPE_MAP.put("AC9EBD8F", "qdf"); //Quicken (qdf)
      FILE_TYPE_MAP.put("E3828596", "pwl"); //Windows Password (pwl)
      FILE_TYPE_MAP.put("2E7261FD", "ram"); //Real Audio (ram)*/


      // images
      FILE_TYPE_MAP.put("FFD8FF", "jpg");
      FILE_TYPE_MAP.put("89504E47", "png");
      FILE_TYPE_MAP.put("47494638", "gif");
      FILE_TYPE_MAP.put("49492A00", "tif");
      FILE_TYPE_MAP.put("424D", "bmp");
      //
      FILE_TYPE_MAP.put("41433130", "dwg"); // CAD
      FILE_TYPE_MAP.put("38425053", "psd");
      FILE_TYPE_MAP.put("7B5C727466", "rtf"); // 日記本
      FILE_TYPE_MAP.put("3C3F786D6C", "xml");
      FILE_TYPE_MAP.put("68746D6C3E", "html");
      FILE_TYPE_MAP.put("44656C69766572792D646174653A", "eml"); // 郵件
      FILE_TYPE_MAP.put("D0CF11E0", "doc");
      FILE_TYPE_MAP.put("5374616E64617264204A", "mdb");
      FILE_TYPE_MAP.put("252150532D41646F6265", "ps");
      FILE_TYPE_MAP.put("255044462D312E", "pdf");
      FILE_TYPE_MAP.put("504B03040A00000000008", "docx");
      FILE_TYPE_MAP.put("504B0304", "zip");// zip 壓縮文件
      FILE_TYPE_MAP.put("52617221", "rar");
      FILE_TYPE_MAP.put("57415645", "wav");
      FILE_TYPE_MAP.put("41564920", "avi");
      FILE_TYPE_MAP.put("2E524D46", "rm");
      FILE_TYPE_MAP.put("000001BA", "mpg");
      FILE_TYPE_MAP.put("000001B3", "mpg");
      FILE_TYPE_MAP.put("6D6F6F76", "mov");
      FILE_TYPE_MAP.put("3026B2758E66CF11", "asf");
      FILE_TYPE_MAP.put("4D546864", "mid");
      FILE_TYPE_MAP.put("1F8B08", "gz");
   }

   public static String getFileType(String url) {
      InputStream is = null;
      try {
         is = new URL(url).openStream();
         byte[] bytes = new byte[10];
         if (is.read(bytes, 0, bytes.length) == -1)
            return null;
         String fileCode = bytesToHexString(bytes).toLowerCase();

         if (fileCode.length() > 1)
            for (String key : FILE_TYPE_MAP.keySet())
               if (fileCode.startsWith(key.toLowerCase()) || key.toLowerCase().startsWith(fileCode))
                  return FILE_TYPE_MAP.get(key);
      } catch (Exception e) {
         e.printStackTrace();
      } finally {
         try {
            if (null != is)
               is.close();
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
      return null;
   }

   /**
    * 獲取文件頭
    *
    * @param src
    * @return
    */
   private static String bytesToHexString(byte[] src) {
      StringBuilder stringBuilder = new StringBuilder();
      if (null == src || src.length < 1)
         return null;
      for (byte b : src) {
         int v = b & 0xFF;
         String hv = Integer.toHexString(v);
         if (hv.length() < 2)
            stringBuilder.append(0);
         stringBuilder.append(hv);
      }
      return stringBuilder.toString();
   }
}