这才是实现分布式锁的正确姿势

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都9102年了，你还在手写分布式锁吗？

经常被问到”如何实现分布式锁”，看来这是大家的一个痛点。

其实Java世界的”半壁江山”——Spring早就提供了分布式锁的实现。早期，分布式锁的相关代码存在于Spring Cloud的子项目Spring Cloud Cluster中，后来被迁到Spring Integration中。

• Spring Cloud Cluster的GitHub： https://github.com/spring-cloud/spring-cloud-cluster ^[1] ， 里面有些用例，以及基于ETCD、hazelcast的分布式锁实现值得一看 。 • Spring Integration的GitHub： https://github.com/spring-projects/spring-integration ^[2]

可能有不少童鞋对Spring Integration不是很熟悉，简单介绍一下——官方说法，这是一个 企业集成模式 的实现；通俗地说，Spring Integration的定位是一个轻量级的ESB，尽管它做了很多ESB不做的事情。顺便说一下，Spring Cloud Stream的底层也是Spring Integration。

Spring Integration提供的全局锁目前为如下存储提供了实现：

• Gemfire ^[4] • JDBC ^[5] • Redis ^[6] • Zookeeper ^[7]

它们使用相同的API抽象——这正是Spring最擅长的。这意味着，不论使用哪种存储，你的编码体验是一样的， 有一天想更换实现，只需要修改依赖和配置就可以了，无需修改代码 。

编码

下面以Redis为例，讲解Spring Integration里面如何使用分布式锁。

1 加依赖

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-integration</artifactId>

</dependency>

<dependency>

<groupId>org.springframework.integration</groupId>

<artifactId>spring-integration-redis</artifactId>

</dependency>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-data-redis</artifactId>

</dependency>

2 写配置：

spring:

redis:

port: 6379

host: localhost

3 写代码：初始化

@Configuration

public class RedisLockConfiguration {

@Bean

public RedisLockRegistry redisLockRegistry(RedisConnectionFactory redisConnectionFactory) {

return new RedisLockRegistry(redisConnectionFactory, "spring-cloud");

}

}

强烈建议阅读一下 org.springframework.integration.redis.util.RedisLockRegistry 的注释， 它详细描述了该类的特性，例如可重入性以及锁在Redis中如何存储等 。

4 写代码：测试

@GetMapping("test")

public void test() throws InterruptedException {

Lock lock = redisLockRegistry.obtain("lock");

boolean b1 = lock.tryLock(3, TimeUnit.SECONDS);

log.info("b1 is : {}", b1);

TimeUnit.SECONDS.sleep(5);

boolean b2 = lock.tryLock(3, TimeUnit.SECONDS);

log.info("b2 is : {}", b2);

lock.unlock();

lock.unlock();

}

测试

1 启动1个实例，访问 http://localhost:8080/test ，会看到类似如下的日志：

2019-03-15 00:48:38.948 INFO 21893 --- [nio-8080-exec-1] c.itmuch.lock.SpringBootLockApplication : b1 is : true

2019-03-15 00:48:43.958 INFO 21893 --- [nio-8080-exec-1] c.itmuch.lock.SpringBootLockApplication : b2 is : true

2 启动2个实例，并迅速访问两个实例的 /test 端点，会在第二个实例上看到类似如下日志：

2019-03-15 00:50:08.222 INFO 21898 --- [nio-8081-exec-3] c.itmuch.lock.SpringBootLockApplication : b1 is : false

2019-03-15 00:50:13.233 INFO 21898 --- [nio-8081-exec-3] c.itmuch.lock.SpringBootLockApplication : b2 is : true

2019-03-15 00:50:13.252 ERROR 21898 --- [nio-8081-exec-3] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalStateException: You do not own lock at spring-cloud:lock] with root cause

java.lang.IllegalStateException: You do not own lock at spring-cloud:lock

at org.springframework.integration.redis.util.RedisLockRegistry$RedisLock.unlock(RedisLockRegistry.java:300) ~[spring-integration-redis-5.1.3.RELEASE.jar:5.1.3.RELEASE]

at com.itmuch.lock.SpringBootLockApplication.test(SpringBootLockApplication.java:33) ~[classes/:na]

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]

at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]

at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.16.jar:9.0.16]

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.16.jar:9.0.16]

at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]

说明第二个实例没有拿到锁，证明了分布式锁的存在。

至此，是不是让你有删掉手写的那些蹩脚的分布式锁的冲动呢？

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References

[1] :  https://github.com/spring-cloud/spring-cloud-cluster

[2] :  https://github.com/spring-projects/spring-integration

[3] Spring Cloud官方:  https://spring.io/projects/spring-cloud

[4] Gemfire:  https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/gemfire.html#gemfire-lock-registry

[5] JDBC:  https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/jdbc.html#jdbc-lock-registry

[6] Redis:  https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/redis.html#redis-lock-registry

[7] Zookeeper:  https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/zookeeper.html#zk-lock-registry