package gboat2.attachment.util;
   
   import java.io.File;
   import java.io.FileInputStream;
   import java.io.IOException;
   import java.io.InputStream;
   import java.security.MessageDigest;
   import java.security.NoSuchAlgorithmException;
   
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public final class MD5Util {
  	/**
  	 * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
  	 */
  	private static char[] hexDigits = { '0', '1', '2', '3', '4', '5', '6',
  			'7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
  	private static MessageDigest messagedigest = null;
  	
  	private static Logger logger = LoggerFactory.getLogger(MD5Util.class);
  	static {
  		try {
  			messagedigest = MessageDigest.getInstance("MD5");
  		} catch (NoSuchAlgorithmException e) {
  			logger.error("初始化MD5失败", e);
  		}
  	}
  
  	public static void main(String[] args) throws IOException {
  		File file = new File("velocity.log");
  		String md5 = getFileMD5String(file);
  		System.out.println("md5:" + md5);
  		File file2 = new File("velocity2.log");
  		String md52 = getFileMD5String(file2);
  		System.out.println("md5:" + md52);
  	}
  
  	public static String getFileMD5String(File file) throws IOException {
  		InputStream fis;
  		fis = new FileInputStream(file);
  		byte[] buffer = new byte[1024];
  		int numRead = 0;
  		while ((numRead = fis.read(buffer)) > 0) {
  			messagedigest.update(buffer, 0, numRead);
  		}
  		fis.close();
  		return bufferToHex(messagedigest.digest());
  	}
  
  	private static String bufferToHex(byte[] bytes) {
  		return bufferToHex(bytes, 0, bytes.length);
  	}
  
  	private static String bufferToHex(byte[] bytes, int m, int n) {
  		StringBuffer stringbuffer = new StringBuffer(2 * n);
  		int k = m + n;
  		for (int l = m; l < k; l++) {
  			appendHexPair(bytes[l], stringbuffer);
  		}
  		return stringbuffer.toString();
  	}
  
  	private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
  		char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换
  		// 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
  		char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换
  		stringbuffer.append(c0);
  		stringbuffer.append(c1);
  	}
  }