加密算法--总结

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最近在给文件做加密时，遇到一些问题，主要是在加密过程中采用加密输入流遇到的问题，总结成代码如下：
package utils;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.nio.ByteBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import org.apache.commons.io.IOUtils;import org.apache.commons.lang.ArrayUtils;public class Test {     protected static MessageDigest messagedigest = null;     static {             try {                     messagedigest = MessageDigest.getInstance("MD5");               } catch (NoSuchAlgorithmException e) {                       e.printStackTrace();             }       }    /**     * ByteArrayOutputStream版本     * 存在问题：当加密文件比较大时会出现内存溢出的问题     * @param file     * @return     */    public static String getFileMD5WithByteArrayOutputStream(File file) {            FileInputStream in = null;            ByteArrayOutputStream out = null;            try {                in = new FileInputStream(file);                   out = new ByteArrayOutputStream((int)file.length());                   byte[] cache = new byte[1024];                   for(int i = in.read(cache);i != -1;i = in.read(cache)){                      out.write(cache, 0, i);                   }                   messagedigest.update(out.toByteArray());                   return changeBase64(messagedigest.digest());              } catch (IOException e) {                e.printStackTrace();            }  finally{                try {                    in.close();                       out.close();                   } catch (IOException e) {                    e.printStackTrace();                }            }            return null;    }    /**     * MappedByteBuffer版本     * 存在问题：当文件加密之后，如果删除会出现文件被占用无法删除的错误     * @param file     * @return     */    public static String getFileMD5WithMappedByteBuffer(File file) {        FileInputStream in = null;        try {            in = new FileInputStream(file);            FileChannel ch = in.getChannel();              MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());              messagedigest.update(byteBuffer);              return changeBase64(messagedigest.digest());          } catch (IOException e) {            e.printStackTrace();        }  finally{            try {                in.close();            } catch (IOException e) {                e.printStackTrace();            }        }        return null;    }    /**      * byteBuffer版本      * @param file      * @return      */    public static String getMD5WithbyteBuffer(File file ){        FileInputStream fis= null;        try{            fis= new FileInputStream(file);            FileChannel fci=  fis.getChannel();            ByteBuffer block= ByteBuffer.allocate(1024);            while(fci.position() < fci.size()){                int readLen= fci.read(block);                block.flip();                messagedigest.update(ArrayUtils.subarray(block.array(), 0, readLen));                   block.clear();            }            return changeBase64(messagedigest.digest());          }catch(IOException e){            e.printStackTrace();        } finally{            IOUtils.closeQuietly(fis);        }        return null;    }    public static void main(String[] args) {         String filePath = "F:\\迅雷下载\\[电影天堂www.dygod.cn].回到未来.[中英双字.1024分辨率].rmvb";         long fileBegin1 = System.currentTimeMillis();         System.out.println("文件加密结果为："+getMD5WithbyteBuffer(new File(filePath)));         long fileEnd1 = System.currentTimeMillis();         System.out.println("文件加密耗时:" + ((fileEnd1 - fileBegin1) / 1000) + "s");         long fileBegin2 = System.currentTimeMillis();         System.out.println("文件加密结果为："+getFileMD5WithMappedByteBuffer(new File(filePath)));         long fileEnd2 = System.currentTimeMillis();         System.out.println("文件加密耗时:" + ((fileEnd2 - fileBegin2) / 1000) + "s");         long fileBegin3 = System.currentTimeMillis();         System.out.println("文件加密结果为："+getFileMD5WithByteArrayOutputStream(new File(filePath)));         long fileEnd3 = System.currentTimeMillis();         System.out.println("文件加密耗时:" + ((fileEnd3 - fileBegin3) / 1000) + "s");    }    //------------------------------加密运算----------------------------------    protected static final byte[] encodingTable =        {            (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',            (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',            (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U',            (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',            (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',            (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',            (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u',            (byte)'v',            (byte)'w', (byte)'x', (byte)'y', (byte)'z',            (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6',            (byte)'7', (byte)'8', (byte)'9',            (byte)'+', (byte)'/'        };    /**     * copy base64的算法     * @param data     * @return     */    public static String changeBase64(byte[] data){        int length = data.length;        int modulus = length % 3;        int dataLength = (length - modulus);        int a1, a2, a3;        StringBuffer buffer = new StringBuffer();        for (int i = 0; i <  dataLength; i += 3)        {            a1 = data[i] & 0xff;            a2 = data[i + 1] & 0xff;            a3 = data[i + 2] & 0xff;            buffer.append(encodingTable[(a1 >>> 2) & 0x3f]);            buffer.append(encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f]);            buffer.append(encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f]);            buffer.append(encodingTable[a3 & 0x3f]);        }        return buffer.toString();    }}
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