MD5Util.java

package com.meng.util;

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;

/**
 * MD5 文字和文件加密工具
 * @author Administrator
 *
 */
public class MD5Util {
    
    protected static char hex[] ={'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 e) {
            e.printStackTrace();
        }
    }
    
    /**
     * 获得文件 MD5 钥匙
     * @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());
        
    }
    
    /**
     * 获得字符串MD5钥匙
     * @param str
     * @return
     */
    public static String getMD5String(String str) {
        return getMD5String(str.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 i = m; i < k; i++) {
            appendHexPair(bytes[i], stringBuffer);
        }
        return stringBuffer.toString();
    }
    
    private static void appendHexPair(byte bt, StringBuffer stringBuffer) {
        char c0 = hex[(bt & 0x0f) >> 4];
        char c1 = hex[bt & 0xf];
        stringBuffer.append(c0);
        stringBuffer.append(c1);
    }
}