md5.java

java写的一个计算文件md5的值的类(支持大文件)

import java.io.File;
import java.io.FileInputStream;
import java.io.RandomAccessFile;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.AccessController;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PrivilegedAction;
import java.util.logging.Level;
import java.util.logging.Logger;


/**
 *
 * @author KO
 */

/**
 * MD5类
 * 
 * @author KO
 */
public class MD5 {

    FileChannel fc = null;
    RandomAccessFile fis = null;
    MappedByteBuffer mbb = null;

    /**
     * 函数名：fileToString 功能：构建文件内存映射
     * 
     * @param filePath -
     *            文件地址
     * @return - 文件内存映射
     */
    public ByteBuffer fileToString(String filePath){

            File f = new File(filePath);

        try {
            fis = new RandomAccessFile(f,"rw");
        } catch (FileNotFoundException ex) {
            throw new RuntimeException("要用MD5加密的文件路径不存在");
        }
            fc = fis.getChannel();
        try {

            mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size());
        } catch (IOException ex) {
            throw new RuntimeException("创建内存映射失败");
        }

        return mbb;

    }

    /**
     * 函数名：calcMD5
     * 
     * @param b -
     *            文件内存映射
     * @return 文件MD5值
     */
    public static void main(String args[]){
    MD5 md5 = new MD5();
        try {
            System.out.println(md5.calcMD5(md5.fileToString("e:\\ds.exe")));
        } catch (MD5Exception ex) {
            Logger.getLogger(MD5.class.getName()).log(Level.SEVERE,null, ex);
        }
    }
    public String calcMD5(ByteBuffer b){
       
            MessageDigest alga = null;
            String tmp = null;
        try {
            alga = MessageDigest.getInstance("MD5");
            alga.update(b);
            
            byte[] digesta = alga.digest();
           
           tmp = byte2hex(digesta);
           return tmp;
           }
         catch (NoSuchAlgorithmException ex) {
           throw new RuntimeException("计算MD5失败!");
        }finally{
            try {
              if (fc != null) {
                fc.close();
                }
              if (fis != null) {
                fis.close();
            }

            } catch (IOException ex) {
                throw new RuntimeException("关闭文件管道资源失败!");
            }
             
            try {
                if (mbb != null) {
                unmap(mbb);
                }
            } catch (Exception ex) {
                throw new RuntimeException("释放文件内存映射失败!");
            }
            return tmp;

        }  
        
        

    }

    /**
     * 函数名：byte2hex 功能：二行制转十六制字符串
     * 
     * @param b -
     *            二进制流
     * @return 十六制字符串
     */
    public String byte2hex(byte[] b)  {

        String hs = "";
        String stmp = "";
        for (int n = 0; n < b.length; n++) {
            stmp = (Integer.toHexString(b[n] & 0XFF));
            if (stmp.length() == 1) {
                hs = hs + "0" + stmp;
            } else {
                hs = hs + stmp;
            }
            if (n < b.length - 1) {
                hs = hs + "";
            }
        }
        // return hs.toUpperCase();
        return hs;
    }

    /**
     * 函数名：unmap 功能：释放指定资源
     * 
     * @param buffer -
     *            要释放的资源
     * @throws java.lang.Exception
     */
    public static void unmap(final Object buffer) throws Exception {
        AccessController.doPrivileged(new PrivilegedAction() {

            public Object run() {
                try {
                    Method getCleanerMethod = buffer.getClass().getMethod(
                            "cleaner", new Class[0]);
                    getCleanerMethod.setAccessible(true);
                    sun.misc.Cleaner cleaner = (sun.misc.Cleaner) getCleanerMethod.invoke(buffer, new Object[0]);
                    cleaner.clean();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            }
        });
    }
}