md5util.java

java实现文件复制粘贴文件的源程序

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {
/**
* 默认的密码字符串组合，apache校验下载的文件的正确性用的就是默认的这个组合
*/
	protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9','a', 'b', 'c', 'd', 'e', 'f' };
	protected static MessageDigest messagedigest = null;
	static{
	   try{
	    messagedigest = MessageDigest.getInstance("MD5");
	   }catch(NoSuchAlgorithmException nsaex){
	    System.err.println(MD5Util.class.getName()+"初始化失败，MessageDigest不支持MD5Util。");
	    nsaex.printStackTrace();
	   }
	}
	
//	public static void main(String[] args) throws IOException {
//	   long begin = System.currentTimeMillis();
//	
//	   File big = new File("F:/java.rar");
//	
//	   String md5=getFileMD5String(big);
//	
//	   long end = System.currentTimeMillis();
//	   System.out.println("md5:"+md5+" time:"+((end-begin)/1000)+"s");
//	}
	
	/**
	* 适用于上G大的文件
	* @param file
	* @return
	* @throws IOException
	*/
	public static String getFileMD5String(File file) throws IOException {
	   FileInputStream in = new FileInputStream(file);
	   FileChannel ch = in.getChannel();
	   MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());
	   messagedigest.update(byteBuffer);
	   return bufferToHex(messagedigest.digest());
	}
	
	public static String getMD5String(String s) {
	   return getMD5String(s.getBytes());
	}
	
	public static String getMD5String(byte[] bytes) {
	   messagedigest.update(bytes);
	   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];
	   char c1 = hexDigits[bt & 0xf];
	   stringbuffer.append(c0);
	   stringbuffer.append(c1);
	}
	
	public static boolean checkPassword(String password, String md5PwdStr) {
	   String s = getMD5String(password);
	   return s.equals(md5PwdStr);
	}
}