Md5Utils.java

package cn.wisenergy.chnmuseum.party.common.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

public class Md5Utils {

    private static final Logger logger = LoggerFactory.getLogger(Md5Utils.class);

    protected static char[] hexDegists = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
    protected static MessageDigest md5 = null;

    static {
        try {
            md5 = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException nsae) {
            logger.info(Md5Utils.class.getName() + "初始化失败，MessageDigest不支持md5!");
            nsae.printStackTrace();
        }
    }

    /**
     * 获取md5校验码
     *
     * @param inputStream
     * @return
     * @throws IOException
     */
    public static String getFileMD5String(java.io.InputStream inputStream) throws IOException {
        // 每次读取1024字节
        byte[] buffer = new byte[1024];
        int readNum = 0;
        while ((readNum = inputStream.read(buffer)) > 0) {
            md5.update(buffer, 0, readNum);
        }
        inputStream.close();
        return bufferToHex(md5.digest());
    }

    /**
     * 更新需要校验的文件输入流
     *
     * @param bs
     * @return
     * @throws IOException
     */
    public static void updateFileMD5String(byte[] bs, int readNum) {
        // 每次读取bs字节，更新MD5输入流
        md5.update(bs, 0, readNum);
    }

    /**
     * 返回md5校验码
     *
     * @return
     * @throws IOException
     */
    public static String getFileMD5String() {
        return bufferToHex(md5.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(n * 2);
        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) {
        // 取字节中高四位进行转换
        char ch0 = hexDegists[(bt & 0xf0) >> 4];
        // 取字节中低四位进行转换
        char ch1 = hexDegists[(bt & 0xf)];
        stringBuffer.append(ch0);
        stringBuffer.append(ch1);
    }

}