33Pay API

<?php
function calculateSign(array $params, string $secretKey): string {
    unset($params['sign']);

    foreach ($params as $k => $v) {
        if ($v === '') {
            unset($params[$k]);
        }
    }

    ksort($params, SORT_STRING);

    $pairs = [];
    foreach ($params as $k => $v) {
        $pairs[] = $k . '=' . $v;
    }

    $signStr = implode('&', $pairs) . '&key=' . $secretKey;
    return strtolower(md5($signStr));
}
?>

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.*;

public class SignUtil {
    public static String calculateSign(Map<String, Object> params, String secretKey) {
        Map<String, Object> filtered = new TreeMap<>();
        for (Map.Entry<String, Object> e : params.entrySet()) {
            String key = e.getKey();
            Object val = e.getValue();
            if ("sign".equalsIgnoreCase(key)) continue;
            if (val instanceof String && ((String) val).isEmpty()) continue;
            filtered.put(key, val);
        }

        StringBuilder sb = new StringBuilder();
        int i = 0;
        for (Map.Entry<String, Object> e : filtered.entrySet()) {
            if (i++ > 0) sb.append("&");
            sb.append(e.getKey()).append("=").append(e.getValue());
        }
        sb.append("&key=").append(secretKey);

        return md5Lower(sb.toString());
    }

    private static String md5Lower(String text) {
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] digest = md.digest(text.getBytes(StandardCharsets.UTF_8));
            StringBuilder out = new StringBuilder();
            for (byte b : digest) out.append(String.format("%02x", b));
            return out.toString();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }
}