在java中用aes256进行加密，但是发现java里面不能使用PKCS7Padding，而java中自带的是PKCS5Padding填充，那解决办法是，通过BouncyCastle组件来让java里面支持PKCS7Padding填充。

説辣么多不如上代码：

public class AESUtil {

/**
* Encodes a String in AES-256 with a given key
*
* @param context
* @param password
* @param text
* @return String Base64 and AES encoded String
*/
public static String encode(String keyString, String stringToEncode) throws NullPointerException {
if (keyString.length() == 0 || keyString == null) {
throw new NullPointerException("Please give Password");
}

if (stringToEncode.length() == 0 || stringToEncode == null) {
throw new NullPointerException("Please give text");
}

try {
SecretKeySpec skeySpec = getKey(keyString);
byte[] clearText = stringToEncode.getBytes("UTF8");

// IMPORTANT TO GET SAME RESULTS ON iOS and ANDROID
final byte[] iv = new byte[16];
Arrays.fill(iv, (byte) 0x00);
IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

/**
* 这个地方调用BouncyCastleProvider
*让java支持PKCS7Padding
*/
Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
// Cipher is not thread safe
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec, ivParameterSpec);

String encrypedValue = Base64.encodeToString(cipher.doFinal(clearText), Base64.DEFAULT);
// Log.d("jacek", "Encrypted: " + stringToEncode + " -> " + encrypedValue);
return encrypedValue;

} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (BadPaddingException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (IllegalBlockSizeException e) {
e.printStackTrace();
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}
return "";
}

/**
* Decodes a String using AES-256 and Base64
*
* @param context
* @param password
* @param text
* @return desoded String
*/
public static String decode(String password, String text) throws NullPointerException {

if (password.length() == 0 || password == null) {
throw new NullPointerException("Please give Password");
}

if (text.length() == 0 || text == null) {
throw new NullPointerException("Please give text");
}

try {
SecretKey key = getKey(password);

// IMPORTANT TO GET SAME RESULTS ON iOS and ANDROID
final byte[] iv = new byte[16];
Arrays.fill(iv, (byte) 0x00);
IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

byte[] encrypedPwdBytes = Base64.decode(text, Base64.DEFAULT);
// cipher is not thread safe

/**
* 这个地方调用BouncyCastleProvider
*让java支持PKCS7Padding
*/
Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
cipher.init(Cipher.DECRYPT_MODE, key, ivParameterSpec);
byte[] decrypedValueBytes = (cipher.doFinal(encrypedPwdBytes));

String decrypedValue = new String(decrypedValueBytes);
//Log.d(LOG_TAG, "Decrypted: " + text + " -> " + decrypedValue);
return decrypedValue;

} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (BadPaddingException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (IllegalBlockSizeException e) {
e.printStackTrace();
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}
return "";
}

/**
* Generates a SecretKeySpec for given password
*
* @param password
* @return SecretKeySpec
* @throws UnsupportedEncodingException
*/
private static SecretKeySpec getKey(String password) throws UnsupportedEncodingException {

// You can change it to 128 if you wish
int keyLength = 256;
byte[] keyBytes = new byte[keyLength / 8];
// explicitly fill with zeros
Arrays.fill(keyBytes, (byte) 0x0);

// if password is shorter then key length, it will be zero-padded
// to key length
byte[] passwordBytes = password.getBytes("UTF-8");
int length = passwordBytes.length < keyBytes.length ? passwordBytes.length : keyBytes.length;
System.arraycopy(passwordBytes, 0, keyBytes, 0, length);
SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");
return key;
}

public static void main(String args[])
{
long startTime = System.currentTimeMillis();
String encodeStr = AESUtil.encode("1234", "你要去哪儿test123");
System.out.println("encoder:"+encodeStr);
String decodeStr = AESUtil.decode("1234",encodeStr);
System.out.println("decoder:"+decodeStr);

}
}

BouncyCastle组件相关jar包bcprov-jdk15on-152.jar的下载地址：http://www.bouncycastle.org

默认 Java 中仅支持 128 位密钥，当使用 256 位密钥的时候，会报告密钥长度错误 你需要下载一个支持更长密钥的包。这个包叫做

Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files 8

，可以从这里下载，下载地址：http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html。下好了zip文件以后，把里面的两个jar包(local_policy.jar,US_export_policy.jar)替换掉jdk的security文件夹中相应的jar包就OK啦。

但是我确实遇到一个比较奇怪的问题，我在android上面调用PKCS7Padding 是没有问题的，但是在java写的服务端就有问题了。不知道为什么，我用的jdk都是1.8.0的jdk。还请各位如果有遇到相同情况的可以解答一下。