原文：http://www.reibang.com/p/6189275403ed

一蹭睡、概念

冪等性, 通俗的說就是一個接口, 多次發(fā)起同一個請求, 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, 可能會多次回調(diào), 必須處理重復(fù)回調(diào)
• 普通表單提交接口, 因為網(wǎng)絡(luò)超時等原因多次點擊提交, 只能成功一次
  等等

二秦踪、常見解決方案

1. 唯一索引 -- 防止新增臟數(shù)據(jù)
2. token機制 -- 防止頁面重復(fù)提交
3. 悲觀鎖 -- 獲取數(shù)據(jù)的時候加鎖(鎖表或鎖行)
4. 樂觀鎖 -- 基于版本號version實現(xiàn), 在更新數(shù)據(jù)那一刻校驗數(shù)據(jù)
5. 分布式鎖 -- redis(jedis蜈敢、redisson)或zookeeper實現(xiàn)
6. 狀態(tài)機 -- 狀態(tài)變更, 更新數(shù)據(jù)時判斷狀態(tài)

三、本文實現(xiàn)

本文采用第2種方式實現(xiàn), 即通過redis + token機制實現(xiàn)接口冪等性校驗

四帚呼、實現(xiàn)思路

為需要保證冪等性的每一次請求創(chuàng)建一個唯一標(biāo)識token, 先獲取token, 并將此token存入redis, 請求接口時, 將此token放到header或者作為請求參數(shù)請求接口, 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)請求, 由于token已被刪除, 則不能通過校驗, 返回請勿重復(fù)操作提示
• 如果不存在, 說明參數(shù)不合法或者是重復(fù)請求, 返回提示即可

五、項目簡介

• springboot
• redis
• @ApiIdempotent注解 + 攔截器對請求進(jìn)行攔截
• @ControllerAdvice全局異常處理
• 壓測工具: jmeter

說明:

• 本文重點介紹冪等性核心實現(xiàn), 關(guān)于springboot如何集成redis、ServerResponse简软、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項目: https://github.com/wangzaiplus/springboot/tree/wxw

六、代碼實現(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 {

    @Autowired
    private 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過期時間
     *
     * @param key
     * @param expireTime 過期時間, 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 {

    @Autowired
    private TokenService tokenService;

    @Override
    public 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, 校驗通過則放行, 校驗失敗則拋出異常, 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);
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
    }

    @Override
    public 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";

    @Autowired
    private JedisUtil jedisUtil;

    @Override
    public 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());
    }

    @Override
    public void checkToken(HttpServletRequest request) {
        String token = request.getHeader(TOKEN_NAME);
        if (StringUtils.isBlank(token)) {// header中不存在token
            token = request.getParameter(TOKEN_NAME);
            if (StringUtils.isBlank(token)) {// parameter中也不存在token
                throw 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
     */
    @Bean
    public 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);
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // 接口冪等性攔截器
        registry.addInterceptor(apiIdempotentInterceptor());
        super.addInterceptors(registry);
    }

    @Bean
    public ApiIdempotentInterceptor apiIdempotentInterceptor() {
        return new ApiIdempotentInterceptor();
    }

}

OK, 目前為止, 校驗代碼準(zhǔn)備就緒, 接下來測試驗證

七述暂、測試驗證

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 {

    @Autowired
    private TokenService tokenService;

    @GetMapping
    public ServerResponse token() {
        return tokenService.createToken();
    }

}

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

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 {

    @Autowired
    private TestService testService;

    @ApiIdempotent
    @PostMapping("testIdempotence")
    public ServerResponse testIdempotence() {
        return testService.testIdempotence();
    }

}

3. 獲取token

   image

查看redis

image

4. 測試接口安全性: 利用jmeter測試工具模擬50個并發(fā)請求, 將上一步獲取到的token作為參數(shù)

   image

image

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, 如token值為"abcd"

   image

八痹升、注意點(非常重要)

image

上圖中, 不能單純的直接刪除token而不校驗是否刪除成功, 會出現(xiàn)并發(fā)安全性問題, 因為, 有可能多個線程同時走到第46行, 此時token還未被刪除, 所以繼續(xù)往下執(zhí)行, 如果不校驗jedisUtil.del(token)的刪除結(jié)果而直接放行, 那么還是會出現(xiàn)重復(fù)提交問題, 即使實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:

image

再次請求

image

再看看控制臺

image

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

九、總結(jié)

其實思路很簡單, 就是每次請求保證唯一性, 從而保證冪等性, 通過攔截器+注解, 就不用每次請求都寫重復(fù)代碼, 其實也可以利用spring aop實現(xiàn), 無所謂

如果小伙伴有什么疑問或者建議歡迎提出

Github
https://github.com/wangzaiplus/springboot/tree/wxw