这才是实现分布式锁的正确姿势！

待我称王封你为后i 2022-02-26 02:14 333阅读 0赞

> 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][https_github.com_spring-cloud_spring-cloud-cluster] ，**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][https_github.com_spring-projects_spring-integration]

> **TIPS**
> 
> 这就是明明 [Spring Cloud官方][Spring Cloud] 说自己实现了 `Global Locks` ，但又无法找到任何相关文档的原因——人家早把相关代码搬迁到Spring Integration了。

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][]
 *  [JDBC][]
 *  [Redis][]
 *  [Zookeeper][]

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**。

> **TIPS**
> 
> 实现无关性：举个例子，你目前有一个基于Redis的分布式锁，但有一天想讲存储改为Consul。此时，统一的API至关重要——**我相信你不会希望仅仅是修改了分布式锁的存储，就得让开发把相关代码翻新一遍**。
> 
> 大学的时候，不也讲过面向接口编程的重要性嘛。
> 
> 因此，即使Spring Integration没有为您使用的存储提供实现(例如Consul)，你也应该基于Spring Integration的API去开发。这样未来的某一天，一旦Spring Integration为你的存储提供支持，**你就可以无痛切换啦**。

## 编码 ##

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

*  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>
    
     
 *  写配置：

spring.redis.port=6379
    spring.redis.host=localhost

*  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**  
    。
 *  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 ##

*  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
    
     
 *  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：
    
    说明第二个实例没有拿到锁，证明了分布式锁的存在  
     
    
        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]
    
    。

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？

[https_github.com_spring-cloud_spring-cloud-cluster]: https://github.com/spring-cloud/spring-cloud-cluster
[https_github.com_spring-projects_spring-integration]: https://github.com/spring-projects/spring-integration
[Spring Cloud]: https://spring.io/projects/spring-cloud
[Gemfire]: https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/gemfire.html#gemfire-lock-registry
[JDBC]: https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/jdbc.html#jdbc-lock-registry
[Redis]: https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/redis.html#redis-lock-registry
[Zookeeper]: https://docs.spring.io/spring-integration/docs/5.1.2.RELEASE/reference/html/zookeeper.html#zk-lock-registry