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<String, Object> LOCK_CACHE = new ConcurrentHashMap<>(200);
private static final ScheduledThreadPoolExecutor EXECUTOR = new ScheduledThreadPoolExecutor(5, new ThreadPoolExecutor.DiscardPolicy());
// private static final Cache<String, Object> 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<BaseResponseDataDTO> saveBbsPosts(@RequestBody @Validated RequestDTO<BbsPostsRequestDTO> 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<Boolean>) 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 <a href="http://redis.io/commands/set">Redis Documentation: SET</a>
*/
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);
}
}
}
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