根据文件的头信息判断文件类型

package test.util;

import java.io.FileInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

 

public final class MD5Util {

/**
  * 把字节数组转换成16进制字符串
  *
  * @param bArray
  * @return 返回大小字母的16进制字符串
  *
  */
 public static final String bytesToHexString(byte[] bArray) {
  StringBuffer sb = new StringBuffer(bArray.length);
  String sTemp;
  for (int i = 0; i < bArray.length; i++) {
   sTemp = Integer.toHexString(0xFF & bArray[i]);
   if (sTemp.length() < 2)
    sb.append(0);
   sb.append(sTemp.toUpperCase());
  }
  return sb.toString();
 }
 /**
  * @param args
  */
 public static void main(String[] args) throws Exception {
  FileInputStream is = new FileInputStream("E://book//gone//让你不再害怕指针.pdf");
  byte[] b = new byte[4];
  is.read(b, 0, b.length);
  System.out.println(bytesToHexString(b));//25504446 :Adobe Acrobat (pdf)，文件头：255044462D312E

 }

}

 

 

package readFileHead;

import java.io.File;
import java.io.FileInputStream;

import javax.swing.filechooser.FileSystemView;

import sun.io.CharToByteUTF8;

public class Read {

 /**
  * 判断文件是否为图片文件(GIF,PNG,JPG)
  *
  * @param srcFileName
  * @return
  */
 public static void  isImage(String srcFileName) {
  FileInputStream imgFile = null;
  byte[] b = new byte[10];
  int l = -1;
  try {
   imgFile = new FileInputStream(srcFileName);
   l = imgFile.read(b);
   imgFile.close();
  } catch (Exception e) {
   e.printStackTrace();
  }
  for (int i = 0; i < b.length; i++) {
   
   System.err.println(b[i]+" = "+Integer.toHexString(b[i])+" = ");
  }
  if (l == 10) {
   byte b0 = b[0];
   byte b1 = b[1];
   byte b2 = b[2];
   byte b3 = b[3];
   byte b6 = b[6];
   byte b7 = b[7];
   byte b8 = b[8];
   byte b9 = b[9];
   if (b0 == (byte) 'G' && b1 == (byte) 'I' && b2 == (byte) 'F') {

    System.out.println("GIF");
   } else if (b1 == (byte) 'P' && b2 == (byte) 'N' && b3 == (byte) 'G') {
    System.out.println("PNG");
   } else if (b6 == (byte) 'J' && b7 == (byte) 'F' && b8 == (byte) 'I' && b9 == (byte) 'F') {
    System.out.println("JPG");
   } else {
    System.out.println("NULL");
   }
  } else {
   System.out.println("读取文件失败");
  }
 }

 public static void main(String[] args) {
  
  String file = "E://book//gone//Linux下单网卡绑定多IP与多网卡共用单IP.doc";
  isImage(file);
  String fileType = FileSystemView.getFileSystemView().getSystemTypeDescription(new File(file));
  System.err.println("FileSystemView:"+fileType);
 }
}