如何验证 reCAPTCHA V2 Java (Servlet)

这是一个问答风格的帖子，我将同时发布问题和答案。主要原因是我花了相当多的时间寻找验证 recaptcha V2 的最简单方法。因此，我将分享我的知识，以避免进一步浪费开发人员的时间。

如何做一个服务器端验证谷歌的验证码 V2 or 隐形验证码 with Java?

我在用着org.json为此的图书馆。获取jar文件来自here http://central.maven.org/maven2/org/json/json/20140107/json-20140107.jar或阅读docs https://mvnrepository.com/artifact/org.json/json/20140107。将 jar 文件添加到您的项目并导入以下类。

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import org.json.JSONObject;

使用以下方法进行验证。

/**
 * Validates Google reCAPTCHA V2 or Invisible reCAPTCHA.
 *
 * @param secretKey Secret key (key given for communication between your
 * site and Google)
 * @param response reCAPTCHA response from client side.
 * (g-recaptcha-response)
 * @return true if validation successful, false otherwise.
 */
public synchronized boolean isCaptchaValid(String secretKey, String response) {
    try {
        String url = "https://www.google.com/recaptcha/api/siteverify",
                params = "secret=" + secretKey + "&response=" + response;

        HttpURLConnection http = (HttpURLConnection) new URL(url).openConnection();
        http.setDoOutput(true);
        http.setRequestMethod("POST");
        http.setRequestProperty("Content-Type",
                "application/x-www-form-urlencoded; charset=UTF-8");
        OutputStream out = http.getOutputStream();
        out.write(params.getBytes("UTF-8"));
        out.flush();
        out.close();

        InputStream res = http.getInputStream();
        BufferedReader rd = new BufferedReader(new InputStreamReader(res, "UTF-8"));

        StringBuilder sb = new StringBuilder();
        int cp;
        while ((cp = rd.read()) != -1) {
            sb.append((char) cp);
        }
        JSONObject json = new JSONObject(sb.toString());
        res.close();

        return json.getBoolean("success");
    } catch (Exception e) {
        //e.printStackTrace();
    }
    return false;
}

调用上面的方法如下图，

if(isCaptchaValid("enter_your_key_here", request.getParameter("g-recaptcha-response"))){
    //valid
}

希望这可以帮助。干杯!

EDIT:使用POST方法来验证信息的建议Google https://developers.google.com/recaptcha/docs/verify#api_request，更安全，但是如果您需要GET方法版本请参考编辑历史记录 https://stackoverflow.com/revisions/47622507/3.

不要编码params多变的。这样做您将始终得到以下响应。

{"error-codes":["missing-input-response","missing-input-secret"],"success":false}