生产级幂等解决方案

之前写过一篇幂等的文章，但是仅仅只是思路，在生产环境肯定还是不能够用的。恰巧同事最近在讨论如何做幂等。那么如何设计幂等能够达到生产可用呢？请看下面代码：

幂等处理接口：

public interface IdempotentProcessor {

    /**
     * 处理幂等执行代码块
     * 
     * @param optType    the opt type
     * @param optId      the opt id
     * @param initStatus the init status
     * @param expireMs   the expire ms
     * @return the status enum
     */
    StatusEnum process(String optType, String optId, StatusEnum initStatus, long expireMs);

    /**
     * 提交幂等
     * @param optType the opt type
     * @param optId   the opt id
     * @return the boolean
     */
    boolean confirm(String optType, String optId);

    /**
     * 
     * 取消幂等
     * @param optType the opt type
     * @param optId   the opt id
     * @return the boolean
     */
    boolean cancel(String optType, String optId);

}
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那么大家看到如上接口设计，会发现当执行process方法时执行幂等且还需要 confim一次,同时可以调用cancel取消幂等。为什么，因为如果在方法执行之前幂等了后续方法执行失败则出大事了。所以需要confirm、cancel两个方法保证最终成功和失败（画外音：此类设计有点TCC事务有木有？）

幂等实现类

public class ItemProcessor implements IdempotentProcessor {

    private static final String CACHE_KEY = "dew:idempotent:item:";

    @Override
    public StatusEnum process(String optType, String optId, StatusEnum initStatus, long expireMs) {
        if (Dew.cluster.cache.setnx(CACHE_KEY + optType + ":" + optId, initStatus.toString(), expireMs / 1000)) {
            // 设置成功，表示之前不存在
            return StatusEnum.NOT_EXIST;
        } else {
            // 设置不成功，表示之前存在，返回存在的值
            String status = Dew.cluster.cache.get(CACHE_KEY + optType + ":" + optId);
            if (status == null || status.isEmpty()) {
                // 设置成功，表示之前不存在
                return StatusEnum.NOT_EXIST;
            } else {
                return StatusEnum.valueOf(status);
            }
        }
    }

    @Override
    public boolean confirm(String optType, String optId) {
        long ttl = Dew.cluster.cache.ttl(CACHE_KEY + optType + ":" + optId);
        if (ttl > 0) {
            Dew.cluster.cache.setex(CACHE_KEY + optType + ":" + optId, StatusEnum.CONFIRMED.toString(), ttl);
        }
        return true;
    }

    @Override
    public boolean cancel(String optType, String optId) {
        Dew.cluster.cache.del(CACHE_KEY + optType + ":" + optId);
        return true;
    }

}
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幂等拦截器

public class IdempotentHandlerInterceptor extends HandlerInterceptorAdapter {

    private DewIdempotentConfig dewIdempotentConfig;

    /**
     * Instantiates a new Idempotent handler interceptor.
     *
     * @param dewIdempotentConfig the dew idempotent config
     */
    public IdempotentHandlerInterceptor(DewIdempotentConfig dewIdempotentConfig) {
        this.dewIdempotentConfig = dewIdempotentConfig;
    }

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        Idempotent idempotent = ((HandlerMethod) handler).getMethod().getAnnotation(Idempotent.class);
        if (idempotent == null) {
            return super.preHandle(request, response, handler);
        }
        // 参数设置
        String optType = "[" + request.getMethod() + "]" + Dew.Info.name + "/" + request.getRequestURI();
        String optIdFlag = StringUtils.isEmpty(idempotent.optIdFlag()) ? dewIdempotentConfig.getDefaultOptIdFlag() : idempotent.optIdFlag();
        String optId = request.getHeader(optIdFlag);
        if (StringUtils.isEmpty(optId)) {
            optId = request.getParameter(optIdFlag);
        }
        if (StringUtils.isEmpty(optId)) {
            // optId不存在，表示忽略幂等检查，强制执行
            return super.preHandle(request, response, handler);
        }
        if (!DewIdempotent.existOptTypeInfo(optType)) {
            long expireMs = idempotent.expireMs() == -1 ? dewIdempotentConfig.getDefaultExpireMs() : idempotent.expireMs();
            boolean needConfirm = idempotent.needConfirm();
            StrategyEnum strategy = idempotent.strategy() == StrategyEnum.AUTO ? dewIdempotentConfig.getDefaultStrategy() : idempotent.strategy();
            DewIdempotent.initOptTypeInfo(optType, needConfirm, expireMs, strategy);
        }
        switch (DewIdempotent.process(optType, optId)) {
            case NOT_EXIST:
                return super.preHandle(request, response, handler);
            case UN_CONFIRM:
                ErrorController.error(request, response, 409,
                        "The last operation was still going on, please wait.", IdempotentException.class.getName());
                return false;
            case CONFIRMED:
                ErrorController.error(request, response, 423,
                        "Resources have been processed, can't repeat the request.", IdempotentException.class.getName());
                return false;
            default:
                return false;
        }
    }

}
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测试用例

测试场景一

第一次请求幂等失败手动取消幂等，第二次幂等成功

代码：

@GetMapping(value = "manual-confirm")
    @Idempotent(expireMs = 5000)
    public Resp<String> testManualConfirm(@RequestParam("str") String str) {
        try {
            if ("dew-test1".equals(str)){
                throw new RuntimeException("处理幂等失败");
            }
            DewIdempotent.confirm();
        } catch (Exception e) {
            DewIdempotent.cancel();
            return Resp.serverError(str + "处理幂等失败");
        }
        return Resp.success(str);
    }
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@Test
public void testConfirm() throws IOException, InterruptedException {
    //幂等唯一键值
    //
    HashMap<String, String> header = new HashMap<String, String>() {
        {
            put(DewIdempotentConfig.DEFAULT_OPT_ID_FLAG, "0001");
        }
    };
    //字符串等于dew-test1幂等失败
    Resp<String> error = Resp.generic($.http.get(urlPre + "manual-confirm?str=dew-test1", header), String.class);
    System.out.println("幂等失败 [errorCode=" + error.getCode() + "-errorMsg=" + error.getMessage() + "]");
    //字符串等于dew-test2幂等成功
    Resp<String> success = Resp.generic($.http.get(urlPre + "manual-confirm?str=dew-test2", header), String.class);
    System.out.println("幂等成功 [code=" + success.getCode() + "-body=" + success.getBody() + "]");
}
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结果：

幂等失败 [errorCode=500-errorMsg=dew-test1处理幂等失败]
幂等成功 [code=200-body=dew-test2]
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测试场景二

第一次请求幂等成功手动提交confim，第二次幂等失败

代码：

@GetMapping(value = "manual-confirm")
@Idempotent(expireMs = 5000)
public Resp<String> testManualConfirm(@RequestParam("str") String str) {
    try {
        DewIdempotent.confirm();
    } catch (Exception e) {
        DewIdempotent.cancel();
        return Resp.serverError(str + "处理幂等失败");
    }
    return Resp.success(str);
}
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@Test
public void testConfirm() throws IOException, InterruptedException {
    //幂等唯一键值
    //
    HashMap<String, String> header = new HashMap<String, String>() {
        {
            put(DewIdempotentConfig.DEFAULT_OPT_ID_FLAG, "0001");
        }
    };
    //字符串等于dew-test1幂等成功
    Resp<String> success = Resp.generic($.http.get(urlPre + "manual-confirm?str=dew-test1", header), String.class);
    System.out.println("幂等成功 [code=" + success.getCode() + "-body=" + success.getBody() + "]");
    Thread.sleep(500);
    //字符串等于dew-test2幂等失败
    Resp<String> error = Resp.generic($.http.get(urlPre + "manual-confirm?str=dew-test2", header), String.class);
    System.out.println("幂等失败 [errorCode=" + error.getCode() + "-errorMsg=" + error.getMessage() + "]");
}
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结果：

幂等成功 [code=200-body=dew-test1]
2019-04-23 00:14:17.123 ERROR 8600 --- [nio-8080-exec-2] ms.dew.core.web.error.ErrorController    : Request [GET-/idempotent/manual-confirm] 169.254.156.20 , error 423 : Resources have been processed, can't repeat the request.
幂等失败 [errorCode=423-errorMsg=[]Resources have been processed, can't repeat the request.]
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