WeChat applet java implements AES decryption and obtains unionId

import org.apache.commons.codec.binary.Base64;import org.bouncycastle.jce.provider.BouncyCastleProvider;import javax.crypto.BadPaddingException;import javax.crypto.Cipher;import javax.crypto.IllegalBlockSizeException;import javax.crypto.NoSuchPaddingException;import javax.crypto.spec.IvParameterSpec;import javax.crypto.spec.SecretKeySpec;import java.security.*;public class AES {    public static boolean initialized = false;    /**
     * AES解密
     * @param content 密文
     * @return
     * @throws InvalidAlgorithmParameterException
     * @throws NoSuchProviderException
     */
    public byte[] decrypt(byte[] content, byte[] keyByte, byte[] ivByte) throws InvalidAlgorithmParameterException {
        initialize();        try {
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
            Key sKeySpec = new SecretKeySpec(keyByte, "AES");
            cipher.init(Cipher.DECRYPT_MODE, sKeySpec, generateIV(ivByte));// 初始化
            byte[] result = cipher.doFinal(content);            return result;
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchPaddingException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        } catch (IllegalBlockSizeException e) {
            e.printStackTrace();
        } catch (BadPaddingException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (Exception e) {            // TODO Auto-generated catch block
            e.printStackTrace();
        }        return null;
    }    public static void initialize(){        if (initialized) return;
        Security.addProvider(new BouncyCastleProvider());
        initialized = true;
    }    //生成iv
    public static AlgorithmParameters generateIV(byte[] iv) throws Exception{
        AlgorithmParameters params = AlgorithmParameters.getInstance("AES");
        params.init(new IvParameterSpec(iv));        return params;
    }
}

import java.nio.charset.Charset;import java.util.Arrays;/**
* Created by Kevin Dong on 2017/1/5.
*/public class WxPKCS7Encoder {    private static final Charset CHARSET = Charset.forName("utf-8");    private static final int BLOCK_SIZE = 32;    /**
     * 获得对明文进行补位填充的字节.
     *
     * @param count 需要进行填充补位操作的明文字节个数
     * @return 补齐用的字节数组
     */
    public static byte[] encode(int count) {        // 计算需要填充的位数
        int amountToPad = BLOCK_SIZE - (count % BLOCK_SIZE);        if (amountToPad == 0) {
            amountToPad = BLOCK_SIZE;
        }        // 获得补位所用的字符
        char padChr = chr(amountToPad);
        String tmp = new String();        for (int index = 0; index < amountToPad; index++) {
            tmp += padChr;
        }        return tmp.getBytes(CHARSET);
    }    /**
     * 删除解密后明文的补位字符
     *
     * @param decrypted 解密后的明文
     * @return 删除补位字符后的明文
     */
    public static byte[] decode(byte[] decrypted) {        int pad = decrypted[decrypted.length - 1];        if (pad < 1 || pad > 32) {
            pad = 0;
        }        return Arrays.copyOfRange(decrypted, 0, decrypted.length - pad);
    }    /**
     * 将数字转化成ASCII码对应的字符，用于对明文进行补码
     *
     * @param a 需要转化的数字
     * @return 转化得到的字符
     */
    public static char chr(int a) {        byte target = (byte) (a & 0xFF);        return (char) target;
    }
}

WechatOpenIdRes wechatInfo  = getWehatInfoByCode(code);        if(wechatInfo != null && wechatInfo.isOk()){            boolean isNew = true;            try {
                AES aes = new AES();                byte[] resultByte = aes.decrypt(Base64.decodeBase64(encryptedData), Base64.decodeBase64(wechatInfo.getSession_key()), Base64.decodeBase64(iv));                if(null != resultByte && resultByte.length > 0){
                    String userInfo = new String(WxPKCS7Encoder.decode(resultByte));
                    WxInfo wxInfo = GsonUtil.fromGson(userInfo, WxInfo.class);                    if(wxInfo != null) {
                        logger.debug("xxxxxunionid===="+wxInfo.getUnionId());
                    }
                }
            } catch (InvalidAlgorithmParameterException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }

var code ="";
wechat.login()
      .then(function(res){
        code = res.code;        
      })
      .then(function(){        return wechat.getUserInfo();
      })
      .then(function(res){var encryptedData = res.encryptedDatavar iv = res.iv;return userservice.getUserToken(code,encryptedData,iv);
      })