MD5Util校验大型文件

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.springframework.stereotype.Component;
import com.tg.exception.DataValidException;

@Component
public class MD5Util implements IMD5Util {
    /**
     * 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 e) {
        System.err.println(MD5Util.class.getName() + "初始化失败，MessageDigest不支持MD5Util.");
        e.printStackTrace();
    }
    }

    /**
     * 计算文件的MD5
     * 
     * @param fileName
     *            文件的绝对路径
     * @return
     * @throws IOException
     */
    public String getFileMD5String(String fileName) throws IOException {
    File f = new File(fileName);
    return getFileMD5String(f);
    }

    /**
     * 计算文件的MD5，重载方法
     * 
     * @param file
     *            文件对象
     * @return
     * @throws IOException
     */
    public String getFileMD5String(File file) throws IOException {
    if (!file.exists() || !file.isFile()) {
        throw new DataValidException("不是有效文件！");
    }
    FileInputStream in = new FileInputStream(file);
    byte[] buffer = new byte[1024 * 1024 * 10];
    int len = 0;
    while ((len = in.read(buffer)) > 0) {
        messageDigest.update(buffer, 0, len);
    }
    in.close();
    return bufferToHex(messageDigest.digest());
    }

    private String bufferToHex(byte bytes[]) {
    return bufferToHex(bytes, 0, bytes.length);
    }

    private 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);
    }
    System.out.println("文件MD5值:" + stringbuffer);
    return stringbuffer.toString();
    }

    private void appendHexPair(byte bt, StringBuffer stringbuffer) {
    char c0 = hexDigits[(bt & 0xf0) >> 4];
    char c1 = hexDigits[bt & 0xf];
    stringbuffer.append(c0);
    stringbuffer.append(c1);
    }
}

本例参考自http://zhouzaibao.iteye.com/blog/343870与http://hi.baidu.com/chenxiaowen/blog/item/9a9cb6deb5c2e95dccbf1abe.html