七、Java常用小知识之MD5加密

package com.imooc.util;

import java.io.File;
import java.io.FileInputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
/**
* @author **
* @date 2018/6/9 10:05
*/
public final class Md5Util {
private static final char DIGITS[] = { ‘0’, ‘1’, ‘2’, ‘3’, ‘4’, ‘5’, ‘6’,
‘7’, ‘8’, ‘9’, ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’ };

/**
 * 获取文件的MD5码
 *
 * @param absPath
 *            文件路径
 * @return 文件的MD5码
 */
public static String getFileMD5(String absPath) {
    try {
        File file = new File(absPath);
        MessageDigest mdTemp = MessageDigest.getInstance("MD5");
        FileInputStream fis = new FileInputStream(file);
        FileChannel filechannel = fis.getChannel();
        MappedByteBuffer mbb = filechannel
                .map(FileChannel.MapMode.READ_ONLY, 0, file.length());
        mdTemp.update(mbb);
        byte[] md = mdTemp.digest();
        int j = md.length;
        char str[] = new char[j * 2];
        int k = 0;
        for (int i = 0; i < j; i++) {
            byte byte0 = md[i];
            str[k++] = DIGITS[byte0 >>> 4 & 0xf];
            str[k++] = DIGITS[byte0 & 0xf];
        }
        fis.close();
        return new String(str);
    } catch (Exception e) {
        return "";
    }
}

/**
 * 获取指定字符串的MD5码
 *
 * @param s
 *            字符串
 * @return 字符串的MD5码
 */
public static String getMD5(String s) {
    char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'a', 'b', 'c', 'd', 'e', 'f' };
    try {
        byte[] strTemp = s.getBytes();
        MessageDigest mdTemp = MessageDigest.getInstance("MD5");
        mdTemp.update(strTemp);
        byte[] md = mdTemp.digest();
        int j = md.length;
        char str[] = new char[j * 2];
        int k = 0;
        for (int i = 0; i < j; i++) {
            byte byte0 = md[i];
            str[k++] = hexDigits[byte0 >>> 4 & 0xf];
            str[k++] = hexDigits[byte0 & 0xf];
        }
        return new String(str);
    } catch (Exception e) {
        return null;
    }
}

}