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【Java】快速获取文件MD5值
作者:羽昶 / 发布于2016/5/10/ 869
package com.algorithm.digest;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel.MapMode;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
 
/**
 * 快速获取文件MD5
 * 
 * @author robert
 *
 */
public class DigestUtil {
    public static String fastDigest(File file) {
        FileInputStream input = null;
        try {
            MessageDigest md = MessageDigest.getInstance("md5");
            input = new FileInputStream(file);
            MappedByteBuffer mb = input.getChannel().map(MapMode.READ_ONLY, 0, file.length());
            md.update(mb);
            return bytesTohex(md.digest());
 
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                if (input != null) {
                    input.close();
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return null;
    }
 
    public static String getFileMD5(File file) {
        MessageDigest digest = null;
        FileInputStream in = null;
        byte buffer[] = new byte[1024];
        int len;
        try {
            digest = MessageDigest.getInstance("MD5");
            in = new FileInputStream(file);
            while ((len = in.read(buffer, 0, 1024)) != -1) {
                digest.update(buffer, 0, len);
            }
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return bytesTohex(digest.digest());
    }
 
    /**
     * 字节转换为Stirng
     * 
     * 快速简单实现方式 BigInteger bigInt = new BigInteger(1, digest.digest()); 
     * return bigInt.toString(16);
     * 
     * @param bytes
     * @return
     */
    public static String bytesTohex(byte[] bytes) {
        StringBuffer strbuf = new StringBuffer();
        for (int i = 0; i < bytes.length; i++) {
            strbuf.append(Character.forDigit((bytes[i] & 0xf0) >> 4, 16));
            strbuf.append(Character.forDigit((bytes[i] & 0x0f), 16));
        }
        return strbuf.toString();
 
    }
}
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