1. MD5加密，常用于加密用户名密码，当用户验证时。

protected byte[] encrypt(byte[] obj) ...{
    try ...{
        MessageDigest md5 = MessageDigest.getInstance("MD5");
            md5.update(obj);
        return md5.digest();
    } catch (NoSuchAlgorithmException e) ...{
        e.printStackTrace();
    }
}

2. SHA加密，与MD5相似的用法，只是两者的算法不同。

protected byte[] encrypt(byte[] obj) ...{
    try ...{
        MessageDigest sha = MessageDigest.getInstance("SHA");
            sha.update(obj);
        return sha.digest();
    } catch (NoSuchAlgorithmException e) ...{
        e.printStackTrace();
    }
}

3. RSA加密，RAS加密允许解密。常用于文本内容的加密。

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import javax.crypto.Cipher;
/** *//**
 * <b>RSAEncrypt</b>
 * <p>
 * @author maqujun
 * @see
 */
public class RSAEncrypt ...{
    /** *//**
 * Main method for RSAEncrypt.
     * @param args
     */
    public static void main(String[] args) ...{
        try ...{
            RSAEncrypt encrypt = new RSAEncrypt();
           
            String encryptText = "encryptText";
            KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
            keyPairGen.initialize(1024);
            KeyPair keyPair = keyPairGen.generateKeyPair();
            // Generate keys
            RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
            RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
            byte[] e = encrypt.encrypt(publicKey, encryptText.getBytes());
            byte[] de = encrypt.decrypt(privateKey,e);
            System.out.println(encrypt.bytesToString(e));
            System.out.println(encrypt.bytesToString(de));
        } catch (Exception e) ...{
            e.printStackTrace();
        }
    }
/** *//**
     * Change byte array to String.
     * @return byte[]
     */
    protected String bytesToString(byte[] encrytpByte) ...{
        String result = "";
        for (Byte bytes : encrytpByte) ...{
            result += (char) bytes.intValue();
        }
        return result;
    }
/** *//**
     * Encrypt String.
     * @return byte[]
     */
    protected byte[] encrypt(RSAPublicKey publicKey, byte[] obj)  ...{
        if (publicKey != null) ...{
            try ...{
                Cipher cipher = Cipher.getInstance("RSA");
                cipher.init(Cipher.ENCRYPT_MODE, publicKey);
                return cipher.doFinal(obj);
            } catch (Exception e) ...{
                e.printStackTrace();
            }
        }
        return null;
    }
    /** *//**
     * Basic decrypt method
     * @return byte[]
     */
    protected byte[] decrypt(RSAPrivateKey privateKey, byte[] obj) ...{
        if (privateKey != null) ...{
                try ...{
                    Cipher cipher = Cipher.getInstance("RSA");
                    cipher.init(Cipher.DECRYPT_MODE, privateKey);
                    return cipher.doFinal(obj);
                } catch (Exception e) ...{
                    e.printStackTrace();
                }
            }
   
        return null;
    }
}