java中如何给文件加密

1、根据自己定的加密算法，从文件流中读取字节进行加密

2、将加密后的字节写入文件。

md5加密：

package com.ncs.pki.util;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Test {
 private static MessageDigest digest = null;
 public synchronized static final String hash(String data) {
  if (digest == null) {
   try {
    digest = MessageDigest.getInstance("MD5");
   } catch (NoSuchAlgorithmException nsae) {
    System.err.println(
     "Failed to load the MD5 MessageDigest. "
      + "Jive will be unable to function normally.");
    nsae.printStackTrace();
   }
  }
  // Now, compute hash.
  digest.update(data.getBytes());
  return encodeHex(digest.digest());
 }
 public static final String encodeHex(byte[] bytes) {
  StringBuffer buf = new StringBuffer(bytes.length * 2);
  int i;

  for (i = 0; i < bytes.length; i++) {
   if (((int) bytes[i] & 0xff) < 0x10) {
    buf.append("0");
   }
   buf.append(Long.toString((int) bytes[i] & 0xff, 16));
  }
  return buf.toString();
 }
 public static String test(){
  return null;
 }
 /**
  * @param args
  */
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  System.out.println(MD5Test.hash("123456"));
 }

}

3des加密：

package com.ncs.pki.util;

import java.security.Key;
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class DesEncrypt {
 /**
  * 
  * 使用DES加密与解密,可对byte[],String类型进行加密与解密 密文可使用String,byte[]存储.
  * 
  * 方法: void getKey(String strKey)从strKey的字条生成一个Key
  * 
  * String getEncString(String strMing)对strMing进行加密,返回String密文 String
  * getDesString(String strMi)对strMin进行解密,返回String明文
  * 
  *byte[] getEncCode(byte[] byteS)byte[]型的加密 byte[] getDesCode(byte[]
  * byteD)byte[]型的解密
  */

 Key key;

 /**
  * 根据参数生成KEY
  * 
  * @param strKey
  */
 public void getKey(String strKey) {
  try {
   KeyGenerator _generator = KeyGenerator.getInstance("DES");
   _generator.init(new SecureRandom(strKey.getBytes()));
   this.key = _generator.generateKey();
   _generator = null;
  } catch (Exception e) {
   e.printStackTrace();
  }
 }

 /**
  * 加密String明文输入,String密文输出
  * 
  * @param strMing
  * @return
  */
 public String getEncString(String strMing) {

  byte[] byteMi = null;
  byte[] byteMing = null;
  String strMi = "";
  BASE64Encoder base64en = new BASE64Encoder();
  try {
   byteMing = strMing.getBytes("UTF8");
   byteMi = this.getEncCode(byteMing);
   strMi = base64en.encode(byteMi);
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   base64en = null;
   byteMing = null;
   byteMi = null;
  }
  return strMi;
 }

 /**
  * 解密 以String密文输入,String明文输出
  * 
  * @param strMi
  * @return
  */
 public String getDesString(String strMi) {
  BASE64Decoder base64De = new BASE64Decoder();
  byte[] byteMing = null;
  byte[] byteMi = null;
  String strMing = "";
  try {
   byteMi = base64De.decodeBuffer(strMi);
   byteMing = this.getDesCode(byteMi);
   strMing = new String(byteMing, "UTF8");
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   base64De = null;
   byteMing = null;
   byteMi = null;
  }
  return strMing;
 }

 /**
  * 加密以byte[]明文输入,byte[]密文输出
  * 
  * @param byteS
  * @return
  */
 private byte[] getEncCode(byte[] byteS) {
  byte[] byteFina = null;
  Cipher cipher;
  try {
   cipher = Cipher.getInstance("DES");
   cipher.init(Cipher.ENCRYPT_MODE, key);
   byteFina = cipher.doFinal(byteS);
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   cipher = null;
  }
  return byteFina;
 }

 /**
  * 解密以byte[]密文输入,以byte[]明文输出
  * 
  * @param byteD
  * @return
  */
 private byte[] getDesCode(byte[] byteD) {
  Cipher cipher;
  byte[] byteFina = null;
  try {
   cipher = Cipher.getInstance("DES");
   cipher.init(Cipher.DECRYPT_MODE, key);
   byteFina = cipher.doFinal(byteD);
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   cipher = null;
  }
  return byteFina;
 }

 public static void main(String[] args) {
  System.out.println("des demo");
  DesEncrypt des = new DesEncrypt();// 实例化一个对像
  des.getKey("MYKEY");// 生成密匙
  System.out.println("key=MYKEY");
  String strEnc = des.getEncString("111111");// 加密字符串,返回String的密文
  System.out.println("密文=" + strEnc);
  String strDes = des.getDesString(strEnc);// 把String 类型的密文解密
  System.out.println("明文=" + strDes);
 }
}