Implementing API Idempotency with Spring Boot, Redis, and Custom Annotations

In real-world development, an exposed API may receive multiple requests, so ensuring idempotency—where repeated executions have the same effect as a single execution—is essential to prevent duplicate database operations.

The article outlines several common idempotency strategies, such as unique database indexes, token mechanisms, pessimistic/optimistic locks, and pre‑check queries, and then focuses on a Redis‑based solution.

1. Building a Redis Service

/** * redis工具类 */
@Component
public class RedisService {
    @Autowired
    private RedisTemplate redisTemplate;
    /** * 写入缓存 * @param key * @param value * @return */
    public boolean set(final String key, Object value) {
        boolean result = false;
        try {
            ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue();
            operations.set(key, value);
            result = true;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }
    /** * 写入缓存设置时效时间 * @param key * @param value * @return */
    public boolean setEx(final String key, Object value, Long expireTime) {
        boolean result = false;
        try {
            ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue();
            operations.set(key, value);
            redisTemplate.expire(key, expireTime, TimeUnit.SECONDS);
            result = true;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }
    /** * 判断缓存中是否有对应的value * @param key * @return */
    public boolean exists(final String key) {
        return redisTemplate.hasKey(key);
    }
    /** * 读取缓存 * @param key * @return */
    public Object get(final String key) {
        ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue();
        return operations.get(key);
    }
    /** * 删除对应的value * @param key */
    public boolean remove(final String key) {
        if (exists(key)) {
            Boolean delete = redisTemplate.delete(key);
            return delete;
        }
        return false;
    }
}

2. Defining a Custom Annotation

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface AutoIdempotent {
}

3. Token Service Interface

public interface TokenService {
    /** * 创建token */
    public String createToken();
    /** * 检验token */
    public boolean checkToken(HttpServletRequest request) throws Exception;
}

4. Token Service Implementation

@Service
public class TokenServiceImpl implements TokenService {
    @Autowired
    private RedisService redisService;
    @Override
    public String createToken() {
        String str = RandomUtil.randomUUID();
        StrBuilder token = new StrBuilder();
        try {
            token.append(Constant.Redis.TOKEN_PREFIX).append(str);
            redisService.setEx(token.toString(), token.toString(), 10000L);
            if (StrUtil.isNotEmpty(token.toString())) {
                return token.toString();
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    }
    @Override
    public boolean checkToken(HttpServletRequest request) throws Exception {
        String token = request.getHeader(Constant.TOKEN_NAME);
        if (StrUtil.isBlank(token)) {
            token = request.getParameter(Constant.TOKEN_NAME);
            if (StrUtil.isBlank(token)) {
                throw new ServiceException(Constant.ResponseCode.ILLEGAL_ARGUMENT, 100);
            }
        }
        if (!redisService.exists(token)) {
            throw new ServiceException(Constant.ResponseCode.REPETITIVE_OPERATION, 200);
        }
        boolean remove = redisService.remove(token);
        if (!remove) {
            throw new ServiceException(Constant.ResponseCode.REPETITIVE_OPERATION, 200);
        }
        return true;
    }
}

5. Web Configuration to Register the Interceptor

@Configuration
public class WebConfiguration extends WebMvcConfigurerAdapter {
    @Resource
    private AutoIdempotentInterceptor autoIdempotentInterceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(autoIdempotentInterceptor);
        super.addInterceptors(registry);
    }
}

6. Interceptor Implementation

@Component
public class AutoIdempotentInterceptor implements HandlerInterceptor {
    @Autowired
    private TokenService tokenService;
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        if (!(handler instanceof HandlerMethod)) {
            return true;
        }
        HandlerMethod handlerMethod = (HandlerMethod) handler;
        Method method = handlerMethod.getMethod();
        AutoIdempotent methodAnnotation = method.getAnnotation(AutoIdempotent.class);
        if (methodAnnotation != null) {
            try {
                return tokenService.checkToken(request);
            } catch (Exception ex) {
                ResultVo failedResult = ResultVo.getFailedResult(101, ex.getMessage());
                writeReturnJson(response, JSONUtil.toJsonStr(failedResult));
                throw ex;
            }
        }
        return true;
    }
    // postHandle and afterCompletion omitted for brevity
    private void writeReturnJson(HttpServletResponse response, String json) throws Exception {
        PrintWriter writer = null;
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html; charset=utf-8");
        try {
            writer = response.getWriter();
            writer.print(json);
        } catch (IOException e) {
        } finally {
            if (writer != null) writer.close();
        }
    }
}

7. Test Controller Demonstrating the Flow

@RestController
public class BusinessController {
    @Resource
    private TokenService tokenService;
    @Resource
    private TestService testService;
    @PostMapping("/get/token")
    public String getToken(){
        String token = tokenService.createToken();
        if (StrUtil.isNotEmpty(token)) {
            ResultVo resultVo = new ResultVo();
            resultVo.setCode(Constant.code_success);
            resultVo.setMessage(Constant.SUCCESS);
            resultVo.setData(token);
            return JSONUtil.toJsonStr(resultVo);
        }
        return StrUtil.EMPTY;
    }
    @AutoIdempotent
    @PostMapping("/test/Idempotence")
    public String testIdempotence() {
        String businessResult = testService.testIdempotence();
        if (StrUtil.isNotEmpty(businessResult)) {
            ResultVo successResult = ResultVo.getSuccessResult(businessResult);
            return JSONUtil.toJsonStr(successResult);
        }
        return StrUtil.EMPTY;
    }
}

The article concludes that using Spring Boot, Redis, and a custom annotation provides an elegant, automated way to guarantee API idempotency, preventing duplicate data modifications and reducing unnecessary load on backend services.