如何移除Java代码中的CompletableFuture将异步转为同步并处理响应错误

一、不能直接删除futures.add(CompletableFuture.supplyAsync(()部分 #

核心原因有两点：

• 原方法依赖List<CompletableFuture<String>>类型的入参收集异步任务结果，改成同步后该入参完全无用，方法签名需要先调整
• 原逻辑里supplyAsync包裹的异步执行逻辑、handle绑定的结果/异常处理逻辑是绑定在一起的，直接删除会导致业务逻辑断裂

二、具体改造步骤 #

第一步：修改方法签名 #

删除无用的futures入参，根据业务需要选择返回处理后的结果集合，或者保持无返回：

// 示例方法签名，可根据实际需求调整返回值
private List<String> getClockRequestList(String createdBy, String capacityType, ResourceHierarchy rA, int[] clock_ids, Boolean checkIfCreatingClock, String url)
            throws JsonProcessingException {
    List<String> resultList = new ArrayList<>();
    // 改造后的业务逻辑放在这里
    return resultList;
}

第二步：异步逻辑转同步执行 #

把supplyAsync包裹的HTTP调用逻辑直接拿出顺序执行，handle内的结果处理逻辑直接跟在HTTP调用后面即可，不需要再包CompletableFuture：

for (int clockid : clock_ids) {
    String clockRequest = requestMapperImpl.getClockRequest(createdBy, capacityType, String.valueOf(clockid),
            rA, checkIfCreatingClock);
    String response = null;
    Throwable error = null;
    // 同步执行HTTP请求，移除异步包裹
    try {
        response = genericRestClientImp.httpPostData(clockRequest, url);
        logger.info("Response from EAM is: {}",response);
    } catch (IOException e) {
        logger.error(e);
        error = e;
    }
    // 原handle内的结果处理逻辑完全复用
    String handleResult;
    if (response != null && error == null) {
        if (checkIfCreatingClock) {
            if (response.contains(AppConstant.FAILURE_MSG)) {
                logger.info(responseMapperImpl.responseMessageClock(AppConstant.FAILURE, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageClock(AppConstant.FAILURE, response, rA, clockid);
            } else if (response.contains(AppConstant.STATUS_404)) {
                logger.info(responseMapperImpl.responseMessageClock(AppConstant.STATUS_404, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageClock(AppConstant.STATUS_404, response, rA, clockid);
            } else if (response.contains(AppConstant.SUCCESS_MSG)) {
                logger.info(responseMapperImpl.responseMessageClock(AppConstant.SUCCESS, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageClock(AppConstant.SUCCESS, response, rA, clockid);
            } else {
                logger.info(responseMapperImpl.responseMessageClock(AppConstant.ERROR, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageClock(AppConstant.ERROR, response, rA, clockid);
            }
        } else {
            if (response.contains(AppConstant.SUCCESS) || response.contains(StringUtils.capitalize(AppConstant.SUCCESS))) {
                logger.info(responseMapperImpl.responseMessageTotalCapacity(AppConstant.SUCCESS, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageTotalCapacity(AppConstant.SUCCESS, response, rA, clockid);
            } else if (response.contains(AppConstant.FAILURE) || response.contains(StringUtils.capitalize(AppConstant.FAILURE))) {
                logger.info(responseMapperImpl.responseMessageTotalCapacity(AppConstant.FAILURE, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageTotalCapacity(AppConstant.FAILURE, response, rA, clockid);
            } else {
                logger.info(responseMapperImpl.responseMessageTotalCapacity(AppConstant.ERROR, response, rA, clockid));
                handleResult = responseMapperImpl.responseMessageTotalCapacity(AppConstant.ERROR, response, rA, clockid);
            }
        }
    } else {
        ErrorResponse errorResponse = new ErrorResponse();
        ResponseStatusMsg responseStatusMsg = new ResponseStatusMsg();
        responseStatusMsg.setStatusCode(HttpStatus.NOT_FOUND.value());
        errorResponse.setClockId(clockid);
        errorResponse.setResourceId(rA.getResourceID());
        responseStatusMsg.setError("Failure in getting response from the "+url);
        errorResponse.setResponse(responseStatusMsg);
        List<ErrorResponse> errorList = new ArrayList();
        errorList.add(errorResponse);
        responseObject.setError(errorList);
        logger.info(responseObject.toString());
        handleResult = responseObject.toString();
    }
    // 用结果集合代替原future集合收集处理后的返回值
    resultList.add(handleResult);
}

三、响应和错误处理注意事项 #

• 原异步场景下handle的正常返回、异常捕获逻辑可以100%复用，不需要调整判断规则
• 原异步逻辑中为了把异常传递给handle抛出的RuntimeException可以删掉，同步场景下直接把异常赋值给error变量即可，避免打断整个循环
• 如果业务不需要保留所有处理后的结果，也可以删掉resultList相关逻辑，保持方法无返回即可

内容的提问来源于stack exchange，提问作者Jeevan Gyawali