注解方式优雅的实现 Redisson 分布式锁

1前言

日常开发中，难免遇到一些并发的场景，为了保证接口执行的一致性，通常采用加锁的方式，因为服务是分布式部署模式，本地锁Reentrantlock和Synchnorized这些就先放到一边了，Redis的setnx锁存在无法抱保证原子性的问题就暂时搁且到一边，直接上大招Redisson也是我最近开发项目中基本都在用的缓存，并且也都是用它的分布式锁机制。

2Redisson分布式锁常规使用

关于Redisson的一些基本概念，本章就不做太详细的说明了，有兴趣的小伙伴可以自己去了解下，主要说下加锁的常规使用，Redisson分布式锁是基于Redis的Rlock锁，实现了JavaJUC包下的Lock接口。

Lock

public void getLock(){//获取锁RLock lock = redisson.getLock("Lxlxxx_Lock");try {// 2.加锁lock.lock();} catch (InterruptedException e) {e.getStackTrace();} finally {// 3.解锁lock.unlock();System.out.println("Finally，释放锁成功");}

getLock获取锁，lock.lock进行加锁，会出现的问题就是lock拿不到锁一直等待，会进入阻塞状态，显然这样是不好的。

TryLock

返回boolean类型，和Reentrantlock的tryLock是一个意思，尝试获取锁，获取到就返回true


RLock lock = redisson.getLock(name);
try {if (lock.tryLock(2, 10, TimeUnit.SECONDS)) {//执行业务逻辑} else {System.out.println("已存在");}
} catch (InterruptedException e) {e.printStackTrace();
}finally {
//判断当前线程持有的锁是不是处于锁定状态，锁定状态再进行释放if (this.redissonLock.isHeldByCurrentThread(lockName)) {this.redissonLock.unlock(lockName);}
}

3自定义注解实现锁机制

通常我们都会将redisson实例注入到方法类里面，然后调用加锁方法进行加锁，如果其他业务方法也需要加锁执行，将会产生很多重复代码，由此采用AOP切面的方式，只需要通过注解的方式就能将方法进行加锁处理。另外，搜索公众号Linux就该这样学后台回复“猴子”，获取一份惊喜礼包。

自定义注解

@Documented
@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface DistributedLock {String key() default "";int leaseTime() default 10;boolean autoRelease() default true;String errorDesc() default "系统正常处理，请稍后提交";int waitTime() default 1;
}

切面类实现

@Aspect
@Component
public class DistributedLockHandler {private static final Logger log = LoggerFactory.getLogger(DistributedLockHandler.class);@AutowiredRedissonLock redissonLock;public DistributedLockHandler() {}@Around("@annotation(distributedLock)")public Object around(ProceedingJoinPoint joinPoint, DistributedLock distributedLock) throws Throwable {String lockName = this.getRedisKey(joinPoint, distributedLock);int leaseTime = distributedLock.leaseTime();String errorDesc = distributedLock.errorDesc();int waitTime = distributedLock.waitTime();Object var8;try {boolean lock = this.redissonLock.tryLock(lockName, (long)leaseTime, (long)waitTime);if (!lock) {throw new RuntimeException(errorDesc);}var8 = joinPoint.proceed();} catch (Throwable var12) {log.error("执行业务方法异常", var12);throw var12;} finally {if (this.redissonLock.isHeldByCurrentThread(lockName)) {this.redissonLock.unlock(lockName);}}return var8;}/***  获取加锁的key* @param joinPoint* @param distributedLock* @return*/private String getRedisKey(ProceedingJoinPoint joinPoint, DistributedLock distributedLock) {String key = distributedLock.key();Object[] parameterValues = joinPoint.getArgs();MethodSignature signature = (MethodSignature)joinPoint.getSignature();Method method = signature.getMethod();DefaultParameterNameDiscoverer nameDiscoverer = new DefaultParameterNameDiscoverer();String[] parameterNames = nameDiscoverer.getParameterNames(method);if (StringUtils.isEmpty(key)) {if (parameterNames != null && parameterNames.length > 0) {StringBuffer sb = new StringBuffer();int i = 0;for(int len = parameterNames.length; i < len; ++i) {sb.append(parameterNames[i]).append(" = ").append(parameterValues[i]);}key = sb.toString();} else {key = "redissionLock";}return key;} else {SpelExpressionParser parser = new SpelExpressionParser();Expression expression = parser.parseExpression(key);if (parameterNames != null && parameterNames.length != 0) {EvaluationContext evaluationContext = new StandardEvaluationContext();for(int i = 0; i < parameterNames.length; ++i) {evaluationContext.setVariable(parameterNames[i], parameterValues[i]);}try {Object expressionValue = expression.getValue(evaluationContext);return expressionValue != null && !"".equals(expressionValue.toString()) ? expressionValue.toString() : key;} catch (Exception var13) {return key;}} else {return key;}}}
}