aes加解密前后端-后台

一、web.xml：

　　<filter>
        <filter-name>fastLoginFilter</filter-name>
        <filter-class>com.xxx.xf.common.util.FastLoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>fastLoginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

配置文件中配置一下訪問路徑可以用作過濾時候判斷，可以直接放行和加密不加密操作：

passUrls=.html;.css;.js;/main/img/;/main/common/;/mlsc-upload/service/sys/file/upload;\

其中，訪問靜態資源肯定是直接放行不過濾不加密的；

二、java代碼：

package com.xxx

/**
 * 用於快速登錄的過濾器，僅放行passUrlList中的路徑
 */
public class FastLoginFilter implements Filter {
    public static final String TICKET_ID = "ticketId";
    public static Logger logger = LoggerUtil.getLoggerByName("system", "loginFilter");

    public static String HOME_URL = "/index.html";
    public static String LOGIN_URL = "/login.html";
    public static String INVALID_URL = "/login.html";

    /**
     * 用於攔截快速登錄的請求
     */
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        String requestURL = request.getRequestURI();
        String retUrl = request.getHeader("Referer");

        // 保留未登錄websocket通信
        if(requestURL.indexOf("/websocket/") == -1){
            if(retUrl==null&&!requestURL.equals(LOGIN_URL)||retUrl!=null&&!checkWebReferer(retUrl)){
                response.sendRedirect(LOGIN_URL);
                return;
            }
        }


        if (checkIsPassUrl(requestURL)) {
            chain.doFilter(req, resp);
            return;
        }

        Object ticketId = request.getSession().getAttribute(TICKET_ID);
//        Object ticketId = request.getParameter(TICKET_ID);
        String requestType = request.getHeader("x-requested-with");
        String userAgent = request.getHeader("user-agent");
        if (ticketId == null) {
            if ((requestType != null && requestType.equals("XMLHttpRequest")) || checkApp(userAgent)) {
                writeUnloginInfo((HttpServletResponse) response);
            } else {
                response.sendRedirect(LOGIN_URL);
            }
            return;
        }
        boolean isLogged = this.isLogged(ticketId.toString());
        String checkLoginStatus = request.getParameter("checkLoginStatus");
        if (StringUtils.isNotNullOrEmpty(checkLoginStatus)) {
            resp.getWriter().write(String.valueOf(isLogged));
            return;
        }
        UserInfo userInfo = CacheUtil.getUserByTicket(ticketId.toString(), UserInfo.class);
        if (userInfo != null && StringUtils.isNotNullOrEmpty(userInfo.getUserId())) {
            CacheUtil.refreshTicket(ticketId.toString(), userInfo.getUserId());
            String token = request.getHeader("token");
            String contentType=request.getContentType();
            if("1".equals(ConfigUtil.get("aesOpen"))&&"XMLHttpRequest".equals(requestType)&&StringUtils.isNotNullOrEmpty(token)
                    &&"encryption".equals(token)){ //和前台一樣的判斷是否需要加解密操作
                String requestBodyMw = null;
                String rsaResult=null;
                try {
                    String p="";
                    if("application/json".equals(contentType)){
                        String requestBody = getRequestParam((HttpServletRequest) request);
                        logger.info(requestBody);
                        JSONObject jsonObject=JSONObject.parseObject(requestBody);
                        p=jsonObject.getString("p"); //獲取前台傳的加密之后的參數p
                    }else{
                        p=request.getParameter("p");
                    }
                    requestBodyMw = CryptionUtil.aesDecrypt(p.trim(), ConfigUtil.get("aecKey")); //先將請求參數進行aes解密
                    rsaResult= RSAEncryptUtils.decrypt(requestBodyMw); //再將前台傳的參數進行RSA解密，步驟與前台相反
                } catch (Exception e) {
                    writeUnloginInfo((HttpServletResponse) response);
                    return;
                }
                WrapperedResponse wrapResponse = new WrapperedResponse((HttpServletResponse) response); //封裝的響應對象
                WrapperedRequest wrapRequest = new WrapperedRequest((HttpServletRequest) request, rsaResult); //封裝的請求對象
                chain.doFilter(wrapRequest, wrapResponse); //調用自己框架的過濾器方法，獲取當前用戶之類的
                byte[] data = wrapResponse.getResponseData();
                String resData=new String(data, "utf-8");
                JSONObject resultObj=new JSONObject();
                try {
                    resultObj.put("data",CryptionUtil.aesEncrypt(resData, ConfigUtil.get("aecKey"))); //返回的參數也是aes加密的
                } catch (Exception e) {
                    e.printStackTrace();
                }
                writeResponse(response, resultObj.toJSONString());
                return;
            }
        } else {
            if ((requestType != null && requestType.equals("XMLHttpRequest")) || checkApp(userAgent)) {
                writeUnloginInfo((HttpServletResponse) response);
            } else {
                response.sendRedirect(INVALID_URL);
            }
            return;
        }
        chain.doFilter(req, resp);
        return;
    }

    private boolean checkWebReferer(String retUrl){
        boolean flag=false;
        String configWebReferer=ConfigUtil.get("webReferer");
        String[] webRefererArr=configWebReferer.split(",");
        for(int i=0;i<webRefererArr.length;i++){
            if(retUrl.startsWith(webRefererArr[i])){
                flag=true;
                break;
            }
        }
        return flag;
    }
    private void writeResponse(ServletResponse response, String responseString)
            throws IOException {
        PrintWriter out = response.getWriter();
        response.setContentLength(responseString.length());
        out.print(responseString);
        out.flush();
        out.close();
    }
    private String getRequestParam(HttpServletRequest request){
        ServletInputStream inputStream = null;
        StringBuilder sb = new StringBuilder();
        try {
            inputStream = request.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while ((line = br.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return sb.toString();
    }
    // 獲取請求路徑，如果是：/fastLoginWS，則直接放行
    public boolean checkIsPassUrl(String requestURL) throws IOException, ServletException {
        boolean isPass = false;
        if (StringUtils.isNotNullOrEmpty(requestURL)) {
            // 判斷訪問的路徑是否為路徑放行集合中的路徑，如果含有，則直接放行
            for (String url : ConfigUtil.PASS_URLS) { //配置文件中可以配置一下訪問路徑，用於不用過濾，不用進行加解密操作等
                if (requestURL.indexOf(url) != -1) {
                    isPass = true;
                    break;
                }
            }
        }
        return isPass;
    }
    private boolean checkApp(String userAgent) {
        if (userAgent != null) {
            if (userAgent.indexOf("okhttp") != -1) {
                return true;
            }
            if (userAgent.indexOf("Darwin") != -1) {
                return true;
            }
            if(userAgent.indexOf("MicroMessenger")>-1){
                return true;
            }
        }
        return false;
    }
    private void writeUnloginInfo(HttpServletResponse response) {
        response.setStatus(HttpStatus.UNAUTHORIZED.value()); //設置狀態碼
        response.setContentType(MediaType.APPLICATION_JSON_VALUE); //設置ContentType
        response.setCharacterEncoding("UTF-8"); //避免亂碼
        response.setHeader("Cache-Control", "no-cache, must-revalidate");
        try {
            response.getWriter().write("{\"statusCode\":1001,\"loginUrl\":\"" + LOGIN_URL + "\",\"success\":false,\"msg\":\"用戶身份已經失效! \"}");
        } catch (IOException e) {
            logger.error("與客戶端通訊異常:" + e.getMessage(), e);
        }
    }
    public static boolean isLogged(String ticketId) {
        if (ticketId == null) {
            return false;
        } else {
            return CacheUtil.isExist(CacheUtil.PREFIX_TICKET_USER.concat(ticketId));
        }
    }
    public void init(FilterConfig arg0) throws ServletException {
        String homeUrl = ConfigUtil.get("homeUrl");
        if (StringUtils.isNotNullOrEmpty(homeUrl)) {
            HOME_URL = homeUrl;
        }
        String loginUrl = ConfigUtil.get("loginUrl");
        if (StringUtils.isNotNullOrEmpty(loginUrl)) {
            LOGIN_URL = loginUrl;
        }
        String invalidUrl = ConfigUtil.get("invalidUrl");
        if (StringUtils.isNotNullOrEmpty(invalidUrl)) {
            INVALID_URL = invalidUrl;
        }
    }

    public void destroy() {
    }
}

 封裝請求對象WrapperedRequest：

package com.xxx
import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.*;


public class WrapperedRequest extends HttpServletRequestWrapper {
    private String requestBody = null;
    HttpServletRequest req = null;
    public WrapperedRequest(HttpServletRequest request) {
        super(request);
        this.req = request;
    }

    public WrapperedRequest(HttpServletRequest request, String requestBody) {
        super(request);
        this.requestBody = requestBody;
        this.req = request;
    }

    /*
     * (non-Javadoc)
     *
     * @see javax.servlet.ServletRequestWrapper#getReader()
     */
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new StringReader(requestBody));
    }

    /*
     * (non-Javadoc)
     *
     * @see javax.servlet.ServletRequestWrapper#getInputStream()
     */
    @Override
    public ServletInputStream getInputStream() throws IOException {
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener readListener) {

            }

            private InputStream in = new ByteArrayInputStream(
                    requestBody.getBytes(req.getCharacterEncoding()));

            @Override
            public int read() throws IOException {
                return in.read();
            }
        };
    }

}

 封裝響應對象WrapperedResponse：

package com.xxx

import javax.servlet.ServletOutputStream;
import javax.servlet.WriteListener;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.*;

public class WrapperedResponse extends HttpServletResponseWrapper {
    private ByteArrayOutputStream buffer = null;
    private ServletOutputStream out = null;
    private PrintWriter writer = null;

    public WrapperedResponse(HttpServletResponse resp) throws IOException {
        super(resp);
        buffer = new ByteArrayOutputStream();// 真正存儲數據的流
        out = new WapperedOutputStream(buffer);
        writer = new PrintWriter(new OutputStreamWriter(buffer,
                this.getCharacterEncoding()));
    }

    /** 重載父類獲取outputstream的方法 */
    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return out;
    }

    /** 重載父類獲取writer的方法 */
    @Override
    public PrintWriter getWriter() throws UnsupportedEncodingException {
        return writer;
    }

    /** 重載父類獲取flushBuffer的方法 */
    @Override
    public void flushBuffer() throws IOException {
        if (out != null) {
            out.flush();
        }
        if (writer != null) {
            writer.flush();
        }
    }

    @Override
    public void reset() {
        buffer.reset();
    }

    /** 將out、writer中的數據強制輸出到WapperedResponse的buffer里面，否則取不到數據 */
    public byte[] getResponseData() throws IOException {
        flushBuffer();
        return buffer.toByteArray();
    }

    /** 內部類，對ServletOutputStream進行包裝 */
    private class WapperedOutputStream extends ServletOutputStream {
        private ByteArrayOutputStream bos = null;

        public WapperedOutputStream(ByteArrayOutputStream stream)
                throws IOException {
            bos = stream;
        }

        @Override
        public void write(int b) throws IOException {
            bos.write(b);
        }

        @Override
        public void write(byte[] b) throws IOException {
            bos.write(b, 0, b.length);
        }

        @Override
        public boolean isReady() {
            return false;
        }

        @Override
        public void setWriteListener(WriteListener writeListener) {

        }
    }

}

 aes加解密的java封裝類：

package com.xxx

import java.math.BigInteger;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.codec.binary.Base64;
import org.apache.commons.lang3.StringUtils;

import sun.misc.BASE64Decoder;

/**
 * AES的加密和解密
 * @author libo
 */
public class CryptionUtil {
    //密鑰 (需要前端和后端保持一致)
//    private static String KEY = ConfigUtil.get("aecKey");
    //算法
    private static final String ALGORITHMSTR = "AES/ECB/PKCS5Padding";

    /**
     * aes解密
     * @param encrypt   內容
     * @return
     * @throws Exception
     */
    public static String aesDecrypt(String encrypt) {
        try {
            return aesDecrypt(encrypt, ConfigUtil.get("aecKey"));
        } catch (Exception e) {
            e.printStackTrace();
            return "";
        }
    }

    /**
     * aes加密
     * @param content
     * @return
     * @throws Exception
     */
    public static String aesEncrypt(String content) {
        try {
            return aesEncrypt(content, ConfigUtil.get("aecKey"));
        } catch (Exception e) {
            e.printStackTrace();
            return "";
        }
    }

    /**
     * 將byte[]轉為各種進制的字符串
     * @param bytes byte[]
     * @param radix 可以轉換進制的范圍，從Character.MIN_RADIX到Character.MAX_RADIX，超出范圍后變為10進制
     * @return 轉換后的字符串
     */
    public static String binary(byte[] bytes, int radix){
        return new BigInteger(1, bytes).toString(radix);// 這里的1代表正數
    }

    /**
     * base 64 encode
     * @param bytes 待編碼的byte[]
     * @return 編碼后的base 64 code
     */
    public static String base64Encode(byte[] bytes){
        return Base64.encodeBase64String(bytes);
    }

    /**
     * base 64 decode
     * @param base64Code 待解碼的base 64 code
     * @return 解碼后的byte[]
     * @throws Exception
     */
    public static byte[] base64Decode(String base64Code) throws Exception{
        return StringUtils.isEmpty(base64Code) ? null : new BASE64Decoder().decodeBuffer(base64Code);
    }


    /**
     * AES加密
     * @param content 待加密的內容
     * @param encryptKey 加密密鑰
     * @return 加密后的byte[]
     * @throws Exception
     */
    public static byte[] aesEncryptToBytes(String content, String encryptKey) throws Exception {
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(128);
        Cipher cipher = Cipher.getInstance(ALGORITHMSTR);
        cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(encryptKey.getBytes(), "AES"));

        return cipher.doFinal(content.getBytes("utf-8"));
    }


    /**
     * AES加密為base 64 code
     * @param content 待加密的內容
     * @param encryptKey 加密密鑰
     * @return 加密后的base 64 code
     * @throws Exception
     */
    public static String aesEncrypt(String content, String encryptKey) throws Exception {
        return base64Encode(aesEncryptToBytes(content, encryptKey));
    }

    /**
     * AES解密
     * @param encryptBytes 待解密的byte[]
     * @param decryptKey 解密密鑰
     * @return 解密后的String
     * @throws Exception
     */
    public static String aesDecryptByBytes(byte[] encryptBytes, String decryptKey) throws Exception {
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(128);

        Cipher cipher = Cipher.getInstance(ALGORITHMSTR);
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(decryptKey.getBytes(), "AES"));
        byte[] decryptBytes = cipher.doFinal(encryptBytes);
        return new String(decryptBytes);
    }


    /**
     * 將base 64 code AES解密
     * @param encryptStr 待解密的base 64 code
     * @param decryptKey 解密密鑰
     * @return 解密后的string
     * @throws Exception
     */
    public static String aesDecrypt(String encryptStr, String decryptKey) throws Exception {
        return StringUtils.isEmpty(encryptStr) ? null : aesDecryptByBytes(base64Decode(encryptStr), decryptKey);
    }

    /**
     * 測試
     */
    public static void main(String[] args) throws Exception {
        String content = "123";
        System.out.println("加密前：" + content);
        System.out.println("加密密鑰和解密密鑰：" + ConfigUtil.get("aecKey"));
        String encrypt = aesEncrypt(content, ConfigUtil.get("aecKey"));
        System.out.println("加密后：" + encrypt);
        String decrypt = aesDecrypt(encrypt, ConfigUtil.get("aecKey"));
        System.out.println("解密后：" + decrypt);
    }
}

RSA加解密的java封裝類：

package com.xxx

import org.apache.commons.lang3.StringUtils;

import javax.crypto.Cipher;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.util.ArrayList;

/**
 * RSA幫助類
 * 
 * @author liww
 * 
 */
public class RSAEncryptUtils {

    /**
     * 模
     */
    private static String module = "ybhndrU9d3UJzvD8WSS1chQ2ZLcn7Y/ZF0SZFJbdWxkvZYAcICUzfJBF4SecxG+ia9GseNDoQ30q+mSM5Ae1NaAy2bjmR1esS17AyX/TnSvtZIm0ACIVLIM6ShM+ukMj/TEhugarwHXhiHmEd8ZkMrVu4SW2XPgWjX7yPoEKLFs=";
    
    /**
     * 公鑰指數
     */
    private static String exponentString = "AQAB";
    
    private static String delement = "NXVBNhxh5b6GkukadyVbUJg6sgY39qUgiyIKz4ILt5C9FtEUoxA4zNIPMtQkn4pWKOywIHR8mSYatbDgBa5lPxBemwvu5cMHVIh0sD25AL+jXk29alVOIPVTpZ/0TDgy7jd7psYUIX7EO80TnvJIOaNcGUNo060H9qpo19x2iYE=";

    /**
     * 生成加密后的字節數組
     * 
     * @param value
     *            待加密字符串
     * @param keyXmlString
     *            加密字符串
     * @return
     */
    public static ArrayList<byte[]> encryptToByteArrayList(String value, String keyXmlString) {
        try {
            byte[] modulusBytes = org.apache.commons.codec.binary.Base64.decodeBase64(module);
            byte[] exponentBytes = org.apache.commons.codec.binary.Base64.decodeBase64(exponentString);
            BigInteger modulus = new BigInteger(1, modulusBytes);
            BigInteger exponent = new BigInteger(1, exponentBytes);

            RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent);
            KeyFactory fact = KeyFactory.getInstance("RSA");
            PublicKey pubKey = fact.generatePublic(rsaPubKey);

            Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, pubKey);

            int splitLength = 39;
            ArrayList<byte[]> byteArrayList = new ArrayList<byte[]>();
            int i = 0;
            do
            {
                int Length = ((i + 1) * splitLength) >= value.length() ? (value.length() - i * splitLength) : splitLength;
                byte[] byteArray = cipher.doFinal(value.substring(i * splitLength, Length).getBytes("UTF-8"));
                byteArrayList.add(byteArray);
                i++;
            } while (i * splitLength < value.length());

            return byteArrayList;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;

    }

    /**
     * RSA加密字符串
     * 
     * @param value
     *            需要加密的字符串
     * @param keyXmlString
     *            加密key字符串
     * @return
     */
    public static String encrypt(String value, String keyXmlString)
    {
        ArrayList<byte[]> byteArrayList = encryptToByteArrayList(value, keyXmlString);
        StringBuilder sb = new StringBuilder();
        for (byte[] byteArray : byteArrayList)
        {
            sb.append(bytesToHexString(byteArray));
            sb.append(",");
        }
        if (sb.length() != 0)
        {
            sb.delete(sb.length() - 1, sb.length());
        }
        return sb.toString();
    }

    /**
     * RSA加密字符串
     * 
     * @param value
     *            需要加密的字符串
     * @return
     */
    public static String encrypt(String value)
    {
        return encrypt(value, null);
    }

    public static byte[] Dencrypt(byte[] encrypted) {
        try {
            byte[] expBytes = org.apache.commons.codec.binary.Base64.decodeBase64(delement);
            byte[] modBytes = org.apache.commons.codec.binary.Base64.decodeBase64(module);

            BigInteger modules = new BigInteger(1, modBytes);
            BigInteger exponent = new BigInteger(1, expBytes);

            KeyFactory factory = KeyFactory.getInstance("RSA");
            Cipher cipher = Cipher.getInstance("RSA");

            RSAPrivateKeySpec privSpec = new RSAPrivateKeySpec(modules, exponent);

            PrivateKey privKey = factory.generatePrivate(privSpec);
            cipher.init(Cipher.DECRYPT_MODE, privKey);
            byte[] decrypted = cipher.doFinal(encrypted);
            return decrypted;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * RSA解密字節流
     * 
     * @param byteArrayList
     *            需要解密字節流泛型
     * @param keyXmlString
     *            加密key字符串
     * @return
     * @throws UnsupportedEncodingException
     */
    public static String decrypt(ArrayList<byte[]> byteArrayList, String keyXmlString) throws UnsupportedEncodingException
    {

        StringBuilder sb = new StringBuilder();
        for (byte[] byteArray : byteArrayList)
        {
            sb.append(new String(Dencrypt(byteArray), "UTF-8"));
        }
        return sb.toString();
    }

    /**
     * RSA解密字符串
     * 
     * @param value
     *            需要解密的字符串
     * @param keyXmlString
     *            加密key字符串
     * @return
     * @throws UnsupportedEncodingException
     */
    public static String decrypt(String value, String keyXmlString) throws UnsupportedEncodingException
    {
        ArrayList<byte[]> byteArrayList = new ArrayList<byte[]>();
        if (StringUtils.isNotBlank(value))
        {
            String[] strArray = value.split(",");
            int byteArrayLength = 0;
            byte[] byteArray;
            for (String str : strArray)
            {
                byteArrayLength = str.length() / 2;
                byteArray = new byte[byteArrayLength];
                for (int i = 0; i < byteArrayLength; i++)
                {
                    try {
                        byteArray[i] = Integer.valueOf(str.substring(i * 2, (i + 1) * 2), 16).byteValue();
                    } catch (NumberFormatException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                byteArrayList.add(byteArray);
            }
        }
        return decrypt(byteArrayList, keyXmlString);
    }

    /**
     * RSA解密字符串
     * 
     * @param value
     *            需要解密的字符串
     * @return
     */
    public static String decrypt(String value)
    {
        try {
            return decrypt(value, null);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 將字節數組轉換為16進制字符串. 可以將byte轉換成int，然后利用Integer.toHexString(int)來轉換成16進制字符串。
     * 
     * @param src
     *            字節數組
     * @return hex string
     */
    public static String bytesToHexString(byte[] src) {
        StringBuilder stringBuilder = new StringBuilder("");
        if (src == null || src.length <= 0) {
            return null;
        }
        for (int i = 0; i < src.length; i++) {
            int v = src[i] & 0xFF;
            String hv = Integer.toHexString(v);
            if (hv.length() < 2) {
                stringBuilder.append(0);
            }
            stringBuilder.append(hv);
        }
        return stringBuilder.toString();
    }

    /**
     * 將16進制字符串轉換為數組
     * 
     * @param hexString
     *            16進制字符串
     * @return byte[]
     */
    public static byte[] hexStringToBytes(String hexString) {
        if (hexString == null || hexString.equals("")) {
            return null;
        }
        hexString = hexString.toUpperCase();
        int length = hexString.length() / 2;
        char[] hexChars = hexString.toCharArray();
        byte[] d = new byte[length];
        for (int i = 0; i < length; i++) {
            int pos = i * 2;
            d[i] = (byte) (charToByte(hexChars[pos]) << 4 | charToByte(hexChars[pos + 1]));
        }
        return d;
    }

    /**
     * 將字符轉換為字節
     * 
     * @param c
     *            待轉換的字符
     * @return byte 轉換后的字節
     */
    private static byte charToByte(char c) {
        return (byte) "0123456789ABCDEF".indexOf(c);
    }
}