1. 客户端创建一个请求拦截器，在发送请求之前对参数进行加密处理。

public class EncryptionInterceptor implements Interceptor {

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        RequestBody requestBody = request.body();
        if (requestBody != null) {
            Buffer buffer = new Buffer();
            requestBody.writeTo(buffer);

            // 将 requestBody 转化为字符串并进行加密
            String encryptedString = encrypt(buffer.readUtf8());

            // 将加密后的参数放回 requestBody 中
            RequestBody encryptedBody = RequestBody.create(requestBody.contentType(), encryptedString);
            request = request.newBuilder().method(request.method(), encryptedBody).build();
        }
        return chain.proceed(request);
    }

    // 加密算法
    private String encrypt(String str) {
        try {
            MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
            byte[] hash = messageDigest.digest(str.getBytes("UTF-8"));
            StringBuilder hex = new StringBuilder(hash.length * 2);
            for (byte b : hash) {
                if ((b & 0xFF) < 0x10) hex.append("0");
                hex.append(Integer.toHexString(b & 0xFF));
            }
            return hex.toString();
        } catch (Exception e) {
            return str;
        }
    }
}

2. 服务器端需要对参数进行解密处理，示例代码如下。

public class DecryptionUtils {

    // 解密算法
    public static String decrypt(String encryptedParam) {
        try {
            MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
            byte[] hash = messageDigest.digest(encryptedParam.getBytes("UTF-8"));
            StringBuilder hex = new StringBuilder(hash.length * 2);
            for (byte b : hash) {
                if ((b & 0xFF) < 0x10) hex.append("0");
                hex.append(Integer.toHexString(b & 0xFF));
            }
            return hex.toString();
        } catch (Exception e) {
            return encryptedParam;
        }
    }
}

使用时，在服务器端接收到请求参数后调用解密算法进行解密即可。