一、概念

冪等性, 通俗的說就是一個(gè)接口, 多次發(fā)起同一個(gè)請(qǐng)求, 必須保證操作只能執(zhí)行一次

比如:

• 訂單接口, 不能多次創(chuàng)建訂單
• 支付接口, 重復(fù)支付同一筆訂單只能扣一次錢
• 支付寶回調(diào)接口, 可能會(huì)多次回調(diào), 必須處理重復(fù)回調(diào)
• 普通表單提交接口, 因?yàn)榫W(wǎng)絡(luò)超時(shí)等原因多次點(diǎn)擊提交, 只能成功一次
  等等

二、常見解決方案

唯一索引 -- 防止新增臟數(shù)據(jù)

token機(jī)制 -- 防止頁面重復(fù)提交

悲觀鎖 -- 獲取數(shù)據(jù)的時(shí)候加鎖(鎖表或鎖行)

樂觀鎖 -- 基于版本號(hào)version實(shí)現(xiàn), 在更新數(shù)據(jù)那一刻校驗(yàn)數(shù)據(jù)

分布式鎖 -- redis(jedis、redisson)或zookeeper實(shí)現(xiàn)

狀態(tài)機(jī) -- 狀態(tài)變更, 更新數(shù)據(jù)時(shí)判斷狀態(tài)

三、本文實(shí)現(xiàn)

本文采用第2種方式實(shí)現(xiàn), 即通過redis + token機(jī)制實(shí)現(xiàn)接口冪等性校驗(yàn)

四、實(shí)現(xiàn)思路

為需要保證冪等性的每一次請(qǐng)求創(chuàng)建一個(gè)唯一標(biāo)識(shí)token, 先獲取token, 并將此token存入redis, 請(qǐng)求接口時(shí), 將此token放到header或者作為請(qǐng)求參數(shù)請(qǐng)求接口, 后端接口判斷redis中是否存在此token:

• 如果存在, 正常處理業(yè)務(wù)邏輯, 并從redis中刪除此token, 那么, 如果是重復(fù)請(qǐng)求, 由于token已被刪除, 則不能通過校驗(yàn), 返回請(qǐng)勿重復(fù)操作提示
• 如果不存在, 說明參數(shù)不合法或者是重復(fù)請(qǐng)求, 返回提示即可

五、項(xiàng)目簡(jiǎn)介

• springboot
• redis
• @ApiIdempotent注解 + 攔截器對(duì)請(qǐng)求進(jìn)行攔截
• @ControllerAdvice全局異常處理
• 壓測(cè)工具: jmeter

說明:

• 本文重點(diǎn)介紹冪等性核心實(shí)現(xiàn), 關(guān)于springboot如何集成redis、ServerResponse、ResponseCode等細(xì)枝末節(jié)不在本文討論范圍之內(nèi), 有興趣的小伙伴可以查看我的Github項(xiàng)目:https://github.com/wangzaiplus/springboot/tree/wxw

六、代碼實(shí)現(xiàn)

1.pom

<!-- Redis-Jedis --> <dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>2.9.0</version> </dependency> <!--lombok 本文用到@Slf4j注解, 也可不引用, 自定義log即可--> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.16.10</version> </dependency>

2.JedisUtil

package com.wangzaiplus.test.util; import lombok.extern.slf4j.Slf4j; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import redis.clients.jedis.Jedis; import redis.clients.jedis.JedisPool; @Component @Slf4j public class JedisUtil {@Autowiredprivate JedisPool jedisPool;private Jedis getJedis() {return jedisPool.getResource();}/*** 設(shè)值** @param key* @param value* @return*/public String set(String key, String value) {Jedis jedis = null;try {jedis = getJedis();return jedis.set(key, value);} catch (Exception e) {log.error("set key:{} value:{} error", key, value, e);return null;} finally {close(jedis);}}/*** 設(shè)值** @param key* @param value* @param expireTime 過期時(shí)間, 單位: s* @return*/public String set(String key, String value, int expireTime) {Jedis jedis = null;try {jedis = getJedis();return jedis.setex(key, expireTime, value);} catch (Exception e) {log.error("set key:{} value:{} expireTime:{} error", key, value, expireTime, e);return null;} finally {close(jedis);}}/*** 取值** @param key* @return*/public String get(String key) {Jedis jedis = null;try {jedis = getJedis();return jedis.get(key);} catch (Exception e) {log.error("get key:{} error", key, e);return null;} finally {close(jedis);}}/*** 刪除key** @param key* @return*/public Long del(String key) {Jedis jedis = null;try {jedis = getJedis();return jedis.del(key.getBytes());} catch (Exception e) {log.error("del key:{} error", key, e);return null;} finally {close(jedis);}}/*** 判斷key是否存在** @param key* @return*/public Boolean exists(String key) {Jedis jedis = null;try {jedis = getJedis();return jedis.exists(key.getBytes());} catch (Exception e) {log.error("exists key:{} error", key, e);return null;} finally {close(jedis);}}/*** 設(shè)值key過期時(shí)間** @param key* @param expireTime 過期時(shí)間, 單位: s* @return*/public Long expire(String key, int expireTime) {Jedis jedis = null;try {jedis = getJedis();return jedis.expire(key.getBytes(), expireTime);} catch (Exception e) {log.error("expire key:{} error", key, e);return null;} finally {close(jedis);}}/*** 獲取剩余時(shí)間** @param key* @return*/public Long ttl(String key) {Jedis jedis = null;try {jedis = getJedis();return jedis.ttl(key);} catch (Exception e) {log.error("ttl key:{} error", key, e);return null;} finally {close(jedis);}}private void close(Jedis jedis) {if (null != jedis) {jedis.close();}} }

3.自定義注解@ApiIdempotent

package com.wangzaiplus.test.annotation;import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target;/*** 在需要保證 接口冪等性 的Controller的方法上使用此注解*/ @Target({ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) public @interface ApiIdempotent { }

4.ApiIdempotentInterceptor攔截器

package com.wangzaiplus.test.interceptor;import com.wangzaiplus.test.annotation.ApiIdempotent; import com.wangzaiplus.test.service.TokenService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.method.HandlerMethod; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.lang.reflect.Method;/*** 接口冪等性攔截器*/ public class ApiIdempotentInterceptor implements HandlerInterceptor {@Autowiredprivate TokenService tokenService;@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {if (!(handler instanceof HandlerMethod)) {return true;}HandlerMethod handlerMethod = (HandlerMethod) handler;Method method = handlerMethod.getMethod();ApiIdempotent methodAnnotation = method.getAnnotation(ApiIdempotent.class);if (methodAnnotation != null) {check(request);// 冪等性校驗(yàn), 校驗(yàn)通過則放行, 校驗(yàn)失敗則拋出異常, 并通過統(tǒng)一異常處理返回友好提示}return true;}private void check(HttpServletRequest request) {tokenService.checkToken(request);}@Overridepublic void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {}@Overridepublic void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {} }

5.TokenServiceImpl

package com.wangzaiplus.test.service.impl;import com.wangzaiplus.test.common.Constant; import com.wangzaiplus.test.common.ResponseCode; import com.wangzaiplus.test.common.ServerResponse; import com.wangzaiplus.test.exception.ServiceException; import com.wangzaiplus.test.service.TokenService; import com.wangzaiplus.test.util.JedisUtil; import com.wangzaiplus.test.util.RandomUtil; import lombok.extern.slf4j.Slf4j; import org.apache.commons.lang3.StringUtils; import org.apache.commons.lang3.text.StrBuilder; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;import javax.servlet.http.HttpServletRequest;@Service public class TokenServiceImpl implements TokenService {private static final String TOKEN_NAME = "token";@Autowiredprivate JedisUtil jedisUtil;@Overridepublic ServerResponse createToken() {String str = RandomUtil.UUID32();StrBuilder token = new StrBuilder();token.append(Constant.Redis.TOKEN_PREFIX).append(str);jedisUtil.set(token.toString(), token.toString(), Constant.Redis.EXPIRE_TIME_MINUTE);return ServerResponse.success(token.toString());}@Overridepublic void checkToken(HttpServletRequest request) {String token = request.getHeader(TOKEN_NAME);if (StringUtils.isBlank(token)) {// header中不存在tokentoken = request.getParameter(TOKEN_NAME);if (StringUtils.isBlank(token)) {// parameter中也不存在tokenthrow new ServiceException(ResponseCode.ILLEGAL_ARGUMENT.getMsg());}}if (!jedisUtil.exists(token)) {throw new ServiceException(ResponseCode.REPETITIVE_OPERATION.getMsg());}Long del = jedisUtil.del(token);if (del <= 0) {throw new ServiceException(ResponseCode.REPETITIVE_OPERATION.getMsg());}}}

6.TestApplication

package com.wangzaiplus.test;import com.wangzaiplus.test.interceptor.ApiIdempotentInterceptor; import org.mybatis.spring.annotation.MapperScan; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.annotation.Bean; import org.springframework.web.cors.CorsConfiguration; import org.springframework.web.cors.UrlBasedCorsConfigurationSource; import org.springframework.web.filter.CorsFilter; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;@SpringBootApplication @MapperScan("com.wangzaiplus.test.mapper") public class TestApplication extends WebMvcConfigurerAdapter {public static void main(String[] args) {SpringApplication.run(TestApplication.class, args);}/*** 跨域* @return*/@Beanpublic CorsFilter corsFilter() {final UrlBasedCorsConfigurationSource urlBasedCorsConfigurationSource = new UrlBasedCorsConfigurationSource();final CorsConfiguration corsConfiguration = new CorsConfiguration();corsConfiguration.setAllowCredentials(true);corsConfiguration.addAllowedOrigin("*");corsConfiguration.addAllowedHeader("*");corsConfiguration.addAllowedMethod("*");urlBasedCorsConfigurationSource.registerCorsConfiguration("/**", corsConfiguration);return new CorsFilter(urlBasedCorsConfigurationSource);}@Overridepublic void addInterceptors(InterceptorRegistry registry) {// 接口冪等性攔截器registry.addInterceptor(apiIdempotentInterceptor());super.addInterceptors(registry);}@Beanpublic ApiIdempotentInterceptor apiIdempotentInterceptor() {return new ApiIdempotentInterceptor();}}

OK, 目前為止, 校驗(yàn)代碼準(zhǔn)備就緒, 接下來測(cè)試驗(yàn)證。

七、測(cè)試驗(yàn)證

1.獲取token的控制器TokenController

package com.wangzaiplus.test.controller;import com.wangzaiplus.test.common.ServerResponse; import com.wangzaiplus.test.service.TokenService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController;@RestController @RequestMapping("/token") public class TokenController {@Autowiredprivate TokenService tokenService;@GetMappingpublic ServerResponse token() {return tokenService.createToken();}}

2.TestController, 注意@ApiIdempotent注解, 在需要冪等性校驗(yàn)的方法上聲明此注解即可, 不需要校驗(yàn)的無影響

package com.wangzaiplus.test.controller;import com.wangzaiplus.test.annotation.ApiIdempotent; import com.wangzaiplus.test.common.ServerResponse; import com.wangzaiplus.test.service.TestService; import lombok.extern.slf4j.Slf4j; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.PostMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController;@RestController @RequestMapping("/test") @Slf4j public class TestController {@Autowiredprivate TestService testService;@ApiIdempotent@PostMapping("testIdempotence")public ServerResponse testIdempotence() {return testService.testIdempotence();} }

3.獲取token

查看redis

4.測(cè)試接口安全性: 利用jmeter測(cè)試工具模擬50個(gè)并發(fā)請(qǐng)求, 將上一步獲取到的token作為參數(shù)

5.header或參數(shù)均不傳token, 或者token值為空, 或者token值亂填, 均無法通過校驗(yàn), 如token值為"abcd"

八、注意點(diǎn)(非常重要)

上圖中, 不能單純的直接刪除token而不校驗(yàn)是否刪除成功, 會(huì)出現(xiàn)并發(fā)安全性問題, 因?yàn)? 有可能多個(gè)線程同時(shí)走到第46行, 此時(shí)token還未被刪除, 所以繼續(xù)往下執(zhí)行, 如果不校驗(yàn)jedisUtil.del(token)的刪除結(jié)果而直接放行, 那么還是會(huì)出現(xiàn)重復(fù)提交問題, 即使實(shí)際上只有一次真正的刪除操作, 下面重現(xiàn)一下

稍微修改一下代碼:

再次請(qǐng)求

再看看控制臺(tái)

雖然只有一個(gè)真正刪除掉token, 但由于沒有對(duì)刪除結(jié)果進(jìn)行校驗(yàn), 所以還是有并發(fā)問題, 因此, 必須校驗(yàn)

九、總結(jié)

其實(shí)思路很簡(jiǎn)單, 就是每次請(qǐng)求保證唯一性, 從而保證冪等性, 通過攔截器+注解, 就不用每次請(qǐng)求都寫重復(fù)代碼, 其實(shí)也可以利用spring aop實(shí)現(xiàn), 無所謂。

轉(zhuǎn)自：簡(jiǎn)書 作者：wangzaiplushttps://www.jianshu.com/p/6189275403ed

總結(jié)

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