用檔案頭判斷。直接讀取檔案的前幾個位元組。
常用檔案的檔案頭如下:
JPEG (jpg),檔案頭:FFD8FF
PNG (png),檔案頭:89504E47
GIF (gif),檔案頭:47494638
TIFF (tif),檔案頭:49492A00
Windows Bitmap (bmp),檔案頭:424D
CAD (dwg),檔案頭:41433130
Adobe Photoshop (psd),檔案頭:38425053
Rich Text Format (rtf),檔案頭:7B5C727466
XML (xml),檔案頭:3C3F786D6C
HTML (html),檔案頭:68746D6C3E
Email [thorough only] (eml),檔案頭:44656C69766572792D646174653A
Outlook Express (dbx),檔案頭:CFAD12FEC5FD746F
Outlook (pst),檔案頭:2142444E
MS Word/Excel (xls.or.doc),檔案頭:D0CF11E0
MS Access (mdb),檔案頭:5374616E64617264204A
WordPerfect (wpd),檔案頭:FF575043
Postscript (eps.or.ps),檔案頭:252150532D41646F6265
Adobe Acrobat (pdf),檔案頭:255044462D312E
Quicken (qdf),檔案頭:AC9EBD8F
Windows Password (pwl),檔案頭:E3828596
ZIP Archive (zip),檔案頭:504B0304
RAR Archive (rar),檔案頭:52617221
Wave (wav),檔案頭:57415645
AVI (avi),檔案頭:41564920
Real Audio (ram),檔案頭:2E7261FD
Real Media (rm),檔案頭:2E524D46
MPEG (mpg),檔案頭:000001BA
MPEG (mpg),檔案頭:000001B3
Quicktime (mov),檔案頭:6D6F6F76
Windows Media (asf),檔案頭:3026B2758E66CF11
MIDI (mid),檔案頭:4D546864
package org.test;
import java.io.FileInputStream;
public class Test {
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();
}
/**
* @param args
*/
public static void main(String[] args) throws Exception {
FileInputStream is = new FileInputStream("D://face.jpg");
byte[] b = new byte[3];
is.read(b, 0, b.length);
System.out.println(bytesToHexString(b));
}
}