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一、服务端代码
1、去geetest官网注册并获取id和key 并引入新建geetestlib工具类

在github中clone出最新Demo项目，快速搭建本地应用：

git clone https://github.com/GeeTeam/gt-java-sdk.git
前往 项目主页

引用SDK

将SDK中的目录下的 src/com 目录复制到你的项目中

import com.geetest.sdk.java.GeetestLib;

public class GeetestLib {

protected final String verName = "3.2.0";// SDK版本编号
protected final String sdkLang = "java";// SD的语言类型

protected final String apiUrl = "http://api.geetest.com"; //极验验证API URL
protected final String baseUrl = "api.geetest.com";

protected final String registerUrl = "/register.php"; //register url
protected final String validateUrl = "/validate.php"; //validate url

/**
 * 极验验证二次验证表单数据 chllenge
 */
public static final String FN_GEETEST_CHALLENGE = "geetest_challenge";

/**
 * 极验验证二次验证表单数据 validate
 */
public static final String FN_GEETEST_VALIDATE = "geetest_validate";

/**
 * 极验验证二次验证表单数据 seccode
 */
public static final String FN_GEETEST_SECCODE = "geetest_seccode";

/**
 * 公钥
 */
private String CAPTCHAID = "";

/**
 * 私钥
 */

private String PRIVATEKEY = "";

private String USERID = "";

private String RESPONSESTR = "";

/**
 * 调试开关，是否输出调试日志
 */
public boolean debugCode = true;

/**
 * 极验验证API服务状态Session Key
 */
public String gtServerStatusSessionKey = "gt_server_status";

/**
 * 带参数构造函数
 * 
 * @param captchaId
 * @param privateKey
 */
public GeetestLib(String captchaId, String privateKey) {
    this.CAPTCHAID = captchaId;
    this.PRIVATEKEY = privateKey;
}

/**
 * 获取本次验证初始化返回字符串
 * 
 * @return 初始化结果
 */
public String getResponseStr() {
    return RESPONSESTR;
}

public String getVersionInfo() {
    return verName;
}

/**
 * 预处理失败后的返回格式串
 * 
 * @return
 */
private String getFailPreProcessRes() {

    Long rnd1 = Math.round(Math.random() * 100);
    Long rnd2 = Math.round(Math.random() * 100);
    String md5Str1 = md5Encode(rnd1 + "");
    String md5Str2 = md5Encode(rnd2 + "");
    String challenge = md5Str1 + md5Str2.substring(0, 2);

    return String.format(
            "{\"success\":%s,\"gt\":\"%s\",\"challenge\":\"%s\"}", 0,
            this.CAPTCHAID, challenge);
}

/**
 * 预处理成功后的标准串
 * 
 */
private String getSuccessPreProcessRes(String challenge) {

    gtlog("challenge:" + challenge);
    return String.format(
            "{\"success\":%s,\"gt\":\"%s\",\"challenge\":\"%s\"}", 1,
            this.CAPTCHAID, challenge);
}

/**
 * 验证初始化预处理
 *
 * @return 1表示初始化成功，0表示初始化失败
 */
public int preProcess() {

    if (registerChallenge() != 1) {

        this.RESPONSESTR = this.getFailPreProcessRes();
        return 0;
    }

    return 1;

}

/**
 * 验证初始化预处理
 *
 * @param userid
 * @return 1表示初始化成功，0表示初始化失败
 */
public int preProcess(String userid){

    this.USERID = userid;
    return this.preProcess();
}



/**
 * 用captchaID进行注册，更新challenge
 * 
 * @return 1表示注册成功，0表示注册失败
 */
private int registerChallenge() {
    try {
        String GET_URL = apiUrl + registerUrl+"?gt=" + this.CAPTCHAID;
        if (this.USERID != ""){
            GET_URL = GET_URL + "&user_id=" + this.USERID;
            this.USERID = "";
        }
        gtlog("GET_URL:" + GET_URL);
        String result_str = readContentFromGet(GET_URL);
        gtlog("register_result:" + result_str);
        if (32 == result_str.length()) {

            this.RESPONSESTR = this.getSuccessPreProcessRes(this.md5Encode(result_str + this.PRIVATEKEY));

            return 1;
        } else {
            gtlog("gtServer register challenge failed");
            return 0;
        }
    } catch (Exception e) {
        gtlog("exception:register api");
    }
    return 0;
}

/**
 * 发送请求，获取服务器返回结果
 * 
 * @param getURL
 * @return 服务器返回结果
 * @throws IOException
 */
private String readContentFromGet(String getURL) throws IOException {

    URL getUrl = new URL(getURL);
    HttpURLConnection connection = (HttpURLConnection) getUrl
            .openConnection();

    connection.setConnectTimeout(2000);// 设置连接主机超时（单位：毫秒）
    connection.setReadTimeout(2000);// 设置从主机读取数据超时（单位：毫秒）

    // 建立与服务器的连接，并未发送数据
    connection.connect();

    // 发送数据到服务器并使用Reader读取返回的数据
    StringBuffer sBuffer = new StringBuffer();

    InputStream inStream = null;
    byte[] buf = new byte[1024];
    inStream = connection.getInputStream();
    for (int n; (n = inStream.read(buf)) != -1;) {
        sBuffer.append(new String(buf, 0, n, "UTF-8"));
    }
    inStream.close();
    connection.disconnect();// 断开连接

    return sBuffer.toString();
}




/**
 * 判断一个表单对象值是否为空
 * 
 * @param gtObj
 * @return
 */
protected boolean objIsEmpty(Object gtObj) {
    if (gtObj == null) {
        return true;
    }

    if (gtObj.toString().trim().length() == 0) {
        return true;
    }

    return false;
}

/**
 * 检查客户端的请求是否合法,三个只要有一个为空，则判断不合法
 * 
 * @param request
 * @return
 */
private boolean resquestIsLegal(String challenge, String validate, String seccode) {

    if (objIsEmpty(challenge)) {
        return false;
    }

    if (objIsEmpty(validate)) {
        return false;
    }

    if (objIsEmpty(seccode)) {
        return false;
    }

    return true;
}


/**
 * 服务正常的情况下使用的验证方式,向gt-server进行二次验证,获取验证结果
 * 
 * @param challenge
 * @param validate
 * @param seccode
 * @return 验证结果,1表示验证成功0表示验证失败
 */
public int enhencedValidateRequest(String challenge, String validate, String seccode) { 

    if (!resquestIsLegal(challenge, validate, seccode)) {
        return 0;
    }
    gtlog("request legitimate");

    String host = baseUrl;
    String path = validateUrl;
    int port = 80;
    String query = String.format("seccode=%s&sdk=%s", seccode,
            (this.sdkLang + "_" + this.verName));
    String response = "";

    if (this.USERID != ""){
        query = query + "&user_id=" + this.USERID;
        this.USERID = "";
    }
    gtlog(query);
    try {
        if (validate.length() <= 0) {
            return 0;
        }

        if (!checkResultByPrivate(challenge, validate)) {
            return 0;
        }
        gtlog("checkResultByPrivate");
        response = postValidate(host, path, query, port);

        gtlog("response: " + response);
    } catch (Exception e) {
        e.printStackTrace();
    }

    gtlog("md5: " + md5Encode(seccode));

    if (response.equals(md5Encode(seccode))) {
        return 1;
    } else {
        return 0;
    }
}

/**
 * 服务正常的情况下使用的验证方式,向gt-server进行二次验证,获取验证结果
 * 
 * @param challenge
 * @param validate
 * @param seccode
 * @param userid
 * @return 验证结果,1表示验证成功0表示验证失败
 */
public int enhencedValidateRequest(String challenge, String validate, String seccode, String userid) {  

    this.USERID = userid;
    return this.enhencedValidateRequest(challenge, validate, seccode);
}

/**
 * failback使用的验证方式
 * 
 * @param challenge
 * @param validate
 * @param seccode
 * @return 验证结果,1表示验证成功0表示验证失败
 */
public int failbackValidateRequest(String challenge, String validate, String seccode) {

    gtlog("in failback validate");

    if (!resquestIsLegal(challenge, validate, seccode)) {
        return 0;
    }
    gtlog("request legitimate");

    String[] validateStr = validate.split("_");
    String encodeAns = validateStr[0];
    String encodeFullBgImgIndex = validateStr[1];
    String encodeImgGrpIndex = validateStr[2];


    gtlog(String.format(
            "encode----challenge:%s--ans:%s,bg_idx:%s,grp_idx:%s",
            challenge, encodeAns, encodeFullBgImgIndex, encodeImgGrpIndex));

    int decodeAns = decodeResponse(challenge, encodeAns);
    int decodeFullBgImgIndex = decodeResponse(challenge, encodeFullBgImgIndex);
    int decodeImgGrpIndex = decodeResponse(challenge, encodeImgGrpIndex);

    gtlog(String.format("decode----ans:%s,bg_idx:%s,grp_idx:%s", decodeAns,
            decodeFullBgImgIndex, decodeImgGrpIndex));

    int validateResult = validateFailImage(decodeAns,decodeFullBgImgIndex, decodeImgGrpIndex);

    return validateResult;
}



/**
 *
 * @param ans
 * @param full_bg_index
 * @param img_grp_index
 * @return
 */
private int validateFailImage(int ans, int full_bg_index,
        int img_grp_index) {
    final int thread = 3;// 容差值

    String full_bg_name = md5Encode(full_bg_index + "").substring(0, 9);
    String bg_name = md5Encode(img_grp_index + "").substring(10, 19);

    String answer_decode = "";

    // 通过两个字符串奇数和偶数位拼接产生答案位
    for (int i = 0; i < 9; i++) {
        if (i % 2 == 0) {
            answer_decode += full_bg_name.charAt(i);
        } else if (i % 2 == 1) {
            answer_decode += bg_name.charAt(i);
        } else {
            gtlog("exception");
        }
    }

    String x_decode = answer_decode.substring(4, answer_decode.length());

    int x_int = Integer.valueOf(x_decode, 16);// 16 to 10

    int result = x_int % 200;
    if (result < 40) {
        result = 40;
    }

    if (Math.abs(ans - result) <= thread) {
        return 1;
    } else {
        return 0;
    }
}




/**
 * 解码随机参数
 * 
 * @param encodeStr
 * @param challenge
 * @return
 */
private int decodeResponse(String challenge, String string) {
    if (string.length() > 100) {
        return 0;
    }

    int[] shuzi = new int[] { 1, 2, 5, 10, 50 };
    String chongfu = "";
    HashMap<String, Integer> key = new HashMap<String, Integer>();
    int count = 0;

    for (int i = 0; i < challenge.length(); i++) {
        String item = challenge.charAt(i) + "";

        if (chongfu.contains(item) == true) {
            continue;
        } else {
            int value = shuzi[count % 5];
            chongfu += item;
            count++;
            key.put(item, value);
        }
    }

    int res = 0;

    for (int j = 0; j < string.length(); j++) {
        res += key.get(string.charAt(j) + "");
    }

    res = res - decodeRandBase(challenge);

    return res;

}

/**
 * 输入的两位的随机数字,解码出偏移量
 * 
 * @param randStr
 * @return
 */
private int decodeRandBase(String challenge) {

    String base = challenge.substring(32, 34);
    ArrayList<Integer> tempArray = new ArrayList<Integer>();

    for (int i = 0; i < base.length(); i++) {
        char tempChar = base.charAt(i);
        Integer tempAscii = (int) (tempChar);

        Integer result = (tempAscii > 57) ? (tempAscii - 87)
                : (tempAscii - 48);

        tempArray.add(result);
    }

    int decodeRes = tempArray.get(0) * 36 + tempArray.get(1);
    return decodeRes;

}



/**
 * 输出debug信息，需要开启debugCode
 * 
 * @param message
 */
public void gtlog(String message) {
    if (debugCode) {
        System.out.println("gtlog: " + message);
    }
}

protected boolean checkResultByPrivate(String challenge, String validate) {
    String encodeStr = md5Encode(PRIVATEKEY + "geetest" + challenge);
    return validate.equals(encodeStr);
}

/**
 * 貌似不是Post方式，后面重构时修改名字
 * 
 * @param host
 * @param path
 * @param data
 * @param port
 * @return
 * @throws Exception
 */
protected String postValidate(String host, String path, String data,
        int port) throws Exception {
    String response = "error";

    InetAddress addr = InetAddress.getByName(host);
    Socket socket = new Socket(addr, port);
    BufferedWriter wr = new BufferedWriter(new OutputStreamWriter(
            socket.getOutputStream(), "UTF8"));
    wr.write("POST " + path + " HTTP/1.0\r\n");
    wr.write("Host: " + host + "\r\n");
    wr.write("Content-Type: application/x-www-form-urlencoded\r\n");
    wr.write("Content-Length: " + data.length() + "\r\n");
    wr.write("\r\n"); // 以空行作为分割

    // 发送数据
    wr.write(data);
    wr.flush();

    // 读取返回信息
    BufferedReader rd = new BufferedReader(new InputStreamReader(
            socket.getInputStream(), "UTF-8"));
    String line;
    while ((line = rd.readLine()) != null) {
        response = line;
    }
    wr.close();
    rd.close();
    socket.close();
    return response;
}


/**
 * md5 加密
 * 
 * @time 2014年7月10日 下午3:30:01
 * @param plainText
 * @return
 */
private String md5Encode(String plainText) {
    String re_md5 = new String();
    try {
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(plainText.getBytes());
        byte b[] = md.digest();
        int i;
        StringBuffer buf = new StringBuffer("");
        for (int offset = 0; offset < b.length; offset++) {
            i = b[offset];
            if (i < 0)
                i += 256;
            if (i < 16)
                buf.append("0");
            buf.append(Integer.toHexString(i));
        }

        re_md5 = buf.toString();

    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }
    return re_md5;
}

}
/********************************/
新建一个controller 并使用ajax实时校验
* 从geetest网站获取的KEY和ID
*/
private static final String CAPTCHA_ID = “自己申请”;
private static final String CAPTCHA_KEY = “自己去官网免费申请”;

/**
 * @Title: verifyCaptchaCode
 * @Description: TODO(图片验证码二次验证返回结果)
 * @param @param request
 * @param @param response
 * @param @throws IOException 参数
 * @return void 返回类型
 * @throws
 */
@RequestMapping(value = "/verifyCaptchaCode")
@ResponseBody
public void verifyCaptchaCode(HttpServletRequest request, HttpServletResponse response) throws IOException {
    GeetestLib gtSdk = new GeetestLib(CAPTCHA_ID, CAPTCHA_KEY);
    String challenge = request.getParameter(GeetestLib.FN_GEETEST_CHALLENGE);
    String validate = request.getParameter(GeetestLib.FN_GEETEST_VALIDATE);
    String seccode = request.getParameter(GeetestLib.FN_GEETEST_SECCODE);
    NotifyMsg msg = new NotifyMsg();
    /****************************/
    // 从session中获取gt-server状态
        int gt_server_status_code = (Integer)    request.getSession().getAttribute(gtSdk.gtServerStatusSessionKey);
    // 从session中获取userid
    String userid = SessionUtil.getAttr(request, "USERID").toString();
    int gtResult = 0;
    if (gt_server_status_code == 1) {
        // gt-server正常，向gt-server进行二次验证
        gtResult = gtSdk.enhencedValidateRequest(challenge, validate, seccode, userid);
        log.info("gtResult:" + gtResult);
    } else {
        // gt-server非正常情况下，进行failback模式验证
        log.info("failback:use your own server captcha validate");
        gtResult = gtSdk.failbackValidateRequest(challenge, validate, seccode);
        log.info("gtResult:" + gtResult);
    }
    if (gtResult != 1) {
        // 验证成功
        msg.init(1, "验证失败");
    }
    MethodUtil.toJsonMsg(response, msg.getKey(), msg.getMsg());
}

/**
 * @Title: startValidate
 * @Description: TODO(图片验证码初始验证返回输出验证码)
 * @param @param request
 * @param @param response 参数
 * @return void 返回类型
 * @throws
 */
@RequestMapping(value = "/startCaptcha")
@ResponseBody
public void startValidate(HttpServletRequest request, HttpServletResponse response) {
    GeetestLib gtSdk = new GeetestLib(CAPTCHA_ID, CAPTCHA_KEY);
    String resStr = "{}";
    // 自定义userid
    String userid = "CaptchaCode";
    // 进行验证预处理
    int gtServerStatus = gtSdk.preProcess(userid);
    // 将服务器状态设置到session中
    request.getSession().setAttribute(gtSdk.gtServerStatusSessionKey, gtServerStatus);
    // 将userid设置到session中
    SessionUtil.setAttr(request, "USERID", userid);
    resStr = gtSdk.getResponseStr();
    MethodUtil.toJsonPrint(response, resStr);
}

二、客户端代码
注意，如果您的网站使用https，则只需要将引入极验库的地方换成https协议即可，不需要更改其它地方。例如SDK中的demo要使用https，则将以下代码：

更换成以下代码即可：

这里的话我们新建一个login.jsp 具体代码省略

//新建一个显示验证码DIV
//提交按钮并将BIND事件绑定到按钮中来

下面是JS脚本放在最末尾