package web536.utils;
import java.security.Key;
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;/**
 * 
 * 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
 */public class DesEncrypt

 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
  */
 ///byte明文,加密成byte密文
 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
  */
 //byte密文,加密成byte明文
 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) 
 {
    DesEncrypt dd=new DesEncrypt();
    String mm="aaabbb";
    String aa=dd.getEncString(mm);
    System.out.print(aa);
    String bb=dd.getDesString(aa);
    System.out.print(bb);
 }}
经常报如下错误:
E:\Borland\JBuilder2005\jdk1.4\bin\javaw -classpath "E:\adweb\classes;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-beanutils.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-collections.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-digester.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-fileupload.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-lang.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-logging.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\commons-validator.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\jakarta-oro.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-struts-1.1-lib\struts.jar;E:\Borland\JBuilder2005\thirdparty\jakarta-tomcat-4.1.27-LE-jdk14\common\lib\servlet.jar;E:\java代码\lib-jar\commons-dbcp.jar;E:\Borland\JBuilder2005\jdk1.4\bin\SHOCK.jar;E:\Borland\JBuilder2005\jdk1.4\jre\bin\SHOCK.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\im\indicim.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\im\thaiim.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\ext\dnsns.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\ext\sunjce_provider.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\ext\ldapsec.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\ext\localedata.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\jsse.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\plugin.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\sunrsasign.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\charsets.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\rt.jar;E:\Borland\JBuilder2005\jdk1.4\jre\lib\jce.jar;E:\Borland\JBuilder2005\jdk1.4\jre\javaws\javaws.jar;E:\Borland\JBuilder2005\jdk1.4\lib\tools.jar;E:\Borland\JBuilder2005\jdk1.4\lib\dt.jar;E:\Borland\JBuilder2005\jdk1.4\lib\htmlconverter.jar"  -Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,address=lenovo-4fbce9bd:3606,suspend=y web536.utils.DesEncrypt 
java.lang.NullPointerException at com.sun.crypto.provider.DESCipher.engineGetKeySize(DashoA6275) at javax.crypto.Cipher.init(DashoA6275) at web536.utils.DesEncrypt.getEncCode(DesEncrypt.java:115) at web536.utils.DesEncrypt.getEncString(DesEncrypt.java:57) at web536.utils.DesEncrypt.main(DesEncrypt.java:155)java.lang.NullPointerException at java.io.ByteArrayInputStream.<init>(ByteArrayInputStream.java:89) at sun.misc.CharacterEncoder.encode(CharacterEncoder.java:170) at web536.utils.DesEncrypt.getEncString(DesEncrypt.java:58) at web536.utils.DesEncrypt.main(DesEncrypt.java:155)java.lang.NullPointerException at com.sun.crypto.provider.DESCipher.engineGetKeySize(DashoA6275) at javax.crypto.Cipher.init(DashoA6275) at web536.utils.DesEncrypt.getDesCode(DesEncrypt.java:140) at web536.utils.DesEncrypt.getDesString(DesEncrypt.java:87) at web536.utils.DesEncrypt.main(DesEncrypt.java:157)java.lang.NullPointerException at java.lang.String.<init>(String.java:346) at web536.utils.DesEncrypt.getDesString(DesEncrypt.java:88) at web536.utils.DesEncrypt.main(DesEncrypt.java:157)
57行代码是:   byteMi = this.getEncCode(byteMing);115 行代码是:    cipher.init(Cipher.ENCRYPT_MODE, key);