解决重复提交问题的三种实现方式

1、进入页面发送token给后端保存至redis缓存，提交订单时检查token是否存在，并删除
2、基于单体服务的实现可以借鉴spring源码中ioc容器的实现方式，本地缓存，应用于重复提交问题注意的点：自定义重复提交锁对象（对象要为单例），使用ConcurrentHashMap缓存请求信息加密生成的key，设置解锁key和解锁时间使用定时任务延时执行，
原理:
使用了 ConcurrentHashMap 并发容器 putIfAbsent 方法,和 ScheduledThreadPoolExecutor 定时任务,也可以使用guava cache的机制, gauva中有配有缓存的有效时间也是可以的key的生成
Content-MD5
Content-MD5 是指 Body 的 MD5 值，只有当 Body 非Form表单时才计算MD5，计算方式直接将参数和参数名称统一加密MD5
MD5在一定范围类认为是唯一的近似唯一当然在低并发的情况下足够了
本地锁只适用于单机部署的应用.
①配置注解

import java.lang.annotation.*;
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Resubmit {
    /**
     * 延时时间 在延时多久后可以再次提交
     *
     * @return Time unit is one second
     */
    int delaySeconds() default 20;
}

②实例化锁

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.codec.digest.DigestUtils;

import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * @author lijing
 * 重复提交锁
 */
@Slf4j
public final class ResubmitLock {

    private static final ConcurrentHashMap LOCK_CACHE = new ConcurrentHashMap<>(200);
    private static final ScheduledThreadPoolExecutor EXECUTOR = new ScheduledThreadPoolExecutor(5, new ThreadPoolExecutor.DiscardPolicy());


   // private static final Cache CACHES = CacheBuilder.newBuilder()
            // 最大缓存 100 个
   //          .maximumSize(1000)
            // 设置写缓存后 5 秒钟过期
   //         .expireAfterWrite(5, TimeUnit.SECONDS)
   //         .build();


    private ResubmitLock() {
    }

    /**
     * 静态内部类 单例模式
     *
     * @return
     */
    private static class SingletonInstance {
        private static final ResubmitLock INSTANCE = new ResubmitLock();
    }

    public static ResubmitLock getInstance() {
        return SingletonInstance.INSTANCE;
    }


    public static String handleKey(String param) {
        return DigestUtils.md5Hex(param == null ? "" : param);
    }

    /**
     * 加锁 putIfAbsent 是原子操作保证线程安全
     *
     * @param key   对应的key
     * @param value
     * @return
     */
    public boolean lock(final String key, Object value) {
        return Objects.isNull(LOCK_CACHE.putIfAbsent(key, value));
    }

    /**
     * 延时释放锁 用以控制短时间内的重复提交
     *
     * @param lock         是否需要解锁
     * @param key          对应的key
     * @param delaySeconds 延时时间
     */
    public void unLock(final boolean lock, final String key, final int delaySeconds) {
        if (lock) {
            EXECUTOR.schedule(() -> {
                LOCK_CACHE.remove(key);
            }, delaySeconds, TimeUnit.SECONDS);
        }
    }
}

③AOP 切面

import com.alibaba.fastjson.JSONObject;
import com.cn.xxx.common.annotation.Resubmit;
import com.cn.xxx.common.annotation.impl.ResubmitLock;
import com.cn.xxx.common.dto.RequestDTO;
import com.cn.xxx.common.dto.ResponseDTO;
import com.cn.xxx.common.enums.ResponseCode;
import lombok.extern.log4j.Log4j;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;

/**
 * @ClassName RequestDataAspect
 * @Description 数据重复提交校验
 * @Author lijing
 * @Date 2019/05/16 17:05
 **/
@Log4j
@Aspect
@Component
public class ResubmitDataAspect {

    private final static String DATA = "data";
    private final static Object PRESENT = new Object();

    @Around("@annotation(com.cn.xxx.common.annotation.Resubmit)")
    public Object handleResubmit(ProceedingJoinPoint joinPoint) throws Throwable {
        Method method = ((MethodSignature) joinPoint.getSignature()).getMethod();
        //获取注解信息
        Resubmit annotation = method.getAnnotation(Resubmit.class);
        int delaySeconds = annotation.delaySeconds();
        Object[] pointArgs = joinPoint.getArgs();
        String key = "";
        //获取第一个参数
        Object firstParam = pointArgs[0];
        if (firstParam instanceof RequestDTO) {
            //解析参数
            JSONObject requestDTO = JSONObject.parseObject(firstParam.toString());
            JSONObject data = JSONObject.parseObject(requestDTO.getString(DATA));
            if (data != null) {
                StringBuffer sb = new StringBuffer();
                data.forEach((k, v) -> {
                    sb.append(v);
                });
                //生成加密参数 使用了content_MD5的加密方式
                key = ResubmitLock.handleKey(sb.toString());
            }
        }
        //执行锁
        boolean lock = false;
        try {
            //设置解锁key
            lock = ResubmitLock.getInstance().lock(key, PRESENT);
            if (lock) {
                //放行
                return joinPoint.proceed();
            } else {
                //响应重复提交异常
                return new ResponseDTO<>(ResponseCode.REPEAT_SUBMIT_OPERATION_EXCEPTION);
            }
        } finally {
            //设置解锁key和解锁时间
            ResubmitLock.getInstance().unLock(lock, key, delaySeconds);
        }
    }
}

④注解使用案例

@ApiOperation(value = "保存我的帖子接口", notes = "保存我的帖子接口")
    @PostMapping("/posts/save")
    @Resubmit(delaySeconds = 10)
    public ResponseDTO saveBbsPosts(@RequestBody @Validated RequestDTO requestDto) {
        return bbsPostsBizService.saveBbsPosts(requestDto);
    }

3、使用redis实现分布式锁，集合集群环境
主要实现方式:
熟悉 Redis 的朋友都知道它是线程安全的，我们利用它的特性可以很轻松的实现一个分布式锁，如 opsForValue().setIfAbsent(key,value)它的作用就是如果缓存中没有当前 Key 则进行缓存同时返回 true 反之亦然；

当缓存后给 key 在设置个过期时间，防止因为系统崩溃而导致锁迟迟不释放形成死锁；那么我们是不是可以这样认为当返回 true 我们认为它获取到锁了，在锁未释放的时候我们进行异常的抛出…

package com.battcn.interceptor;

import com.battcn.annotation.CacheLock;
import com.battcn.utils.RedisLockHelper;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.util.StringUtils;

import java.lang.reflect.Method;
import java.util.UUID;

/**
 * redis 方案
 *
 * @author Levin
 * @since 2018/6/12 0012
 */
@Aspect
@Configuration
public class LockMethodInterceptor {

    @Autowired
    public LockMethodInterceptor(RedisLockHelper redisLockHelper, CacheKeyGenerator cacheKeyGenerator) {
        this.redisLockHelper = redisLockHelper;
        this.cacheKeyGenerator = cacheKeyGenerator;
    }

    private final RedisLockHelper redisLockHelper;
    private final CacheKeyGenerator cacheKeyGenerator;


    @Around("execution(public * *(..)) && @annotation(com.battcn.annotation.CacheLock)")
    public Object interceptor(ProceedingJoinPoint pjp) {
        MethodSignature signature = (MethodSignature) pjp.getSignature();
        Method method = signature.getMethod();
        CacheLock lock = method.getAnnotation(CacheLock.class);
        if (StringUtils.isEmpty(lock.prefix())) {
            throw new RuntimeException("lock key don't null...");
        }
        final String lockKey = cacheKeyGenerator.getLockKey(pjp);
        String value = UUID.randomUUID().toString();
        try {
            // 假设上锁成功，但是设置过期时间失效，以后拿到的都是 false
            final boolean success = redisLockHelper.lock(lockKey, value, lock.expire(), lock.timeUnit());
            if (!success) {
                throw new RuntimeException("重复提交");
            }
            try {
                return pjp.proceed();
            } catch (Throwable throwable) {
                throw new RuntimeException("系统异常");
            }
        } finally {
            // TODO 如果演示的话需要注释该代码;实际应该放开
            redisLockHelper.unlock(lockKey, value);
        }

RedisLockHelper 通过封装成 API 方式调用，灵活度更加高

package com.battcn.utils;

import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.RedisStringCommands;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.types.Expiration;
import org.springframework.util.StringUtils;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.regex.Pattern;

/**
 * 需要定义成 Bean
 *
 * @author Levin
 * @since 2018/6/15 0015
 */
@Configuration
@AutoConfigureAfter(RedisAutoConfiguration.class)
public class RedisLockHelper {


    private static final String DELIMITER = "|";

    /**
     * 如果要求比较高可以通过注入的方式分配
     */
    private static final ScheduledExecutorService EXECUTOR_SERVICE = Executors.newScheduledThreadPool(10);

    private final StringRedisTemplate stringRedisTemplate;

    public RedisLockHelper(StringRedisTemplate stringRedisTemplate) {
        this.stringRedisTemplate = stringRedisTemplate;
    }

    /**
     * 获取锁（存在死锁风险）
     *
     * @param lockKey lockKey
     * @param value   value
     * @param time    超时时间
     * @param unit    过期单位
     * @return true or false
     */
    public boolean tryLock(final String lockKey, final String value, final long time, final TimeUnit unit) {
        return stringRedisTemplate.execute((RedisCallback) connection -> connection.set(lockKey.getBytes(), value.getBytes(), Expiration.from(time, unit), RedisStringCommands.SetOption.SET_IF_ABSENT));
    }

    /**
     * 获取锁
     *
     * @param lockKey lockKey
     * @param uuid    UUID
     * @param timeout 超时时间
     * @param unit    过期单位
     * @return true or false
     */
    public boolean lock(String lockKey, final String uuid, long timeout, final TimeUnit unit) {
        final long milliseconds = Expiration.from(timeout, unit).getExpirationTimeInMilliseconds();
        boolean success = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
        if (success) {
            stringRedisTemplate.expire(lockKey, timeout, TimeUnit.SECONDS);
        } else {
            String oldVal = stringRedisTemplate.opsForValue().getAndSet(lockKey, (System.currentTimeMillis() + milliseconds) + DELIMITER + uuid);
            final String[] oldValues = oldVal.split(Pattern.quote(DELIMITER));
            if (Long.parseLong(oldValues[0]) + 1 <= System.currentTimeMillis()) {
                return true;
            }
        }
        return success;
    }


    /**
     * @see Redis Documentation: SET
     */
    public void unlock(String lockKey, String value) {
        unlock(lockKey, value, 0, TimeUnit.MILLISECONDS);
    }

    /**
     * 延迟unlock
     *
     * @param lockKey   key
     * @param uuid      client(最好是唯一键的)
     * @param delayTime 延迟时间
     * @param unit      时间单位
     */
    public void unlock(final String lockKey, final String uuid, long delayTime, TimeUnit unit) {
        if (StringUtils.isEmpty(lockKey)) {
            return;
        }
        if (delayTime <= 0) {
            doUnlock(lockKey, uuid);
        } else {
            EXECUTOR_SERVICE.schedule(() -> doUnlock(lockKey, uuid), delayTime, unit);
        }
    }

    /**
     * @param lockKey key
     * @param uuid    client(最好是唯一键的)
     */
    private void doUnlock(final String lockKey, final String uuid) {
        String val = stringRedisTemplate.opsForValue().get(lockKey);
        final String[] values = val.split(Pattern.quote(DELIMITER));
        if (values.length <= 0) {
            return;
        }
        if (uuid.equals(values[1])) {
            stringRedisTemplate.delete(lockKey);
        }
    }

}

转载自：https://www.cnblogs.com/javazhiyin/p/11407140.html

解决重复提交问题的三种实现方式

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