redisTemplate 使用 setIfAbsent 返回 null 问题原理及解决办法

redisTemplate 使用 setIfAbsent 返回 null 问题原理及解决办法

1.简介

有的时候我们使用 redisTemplate给锁设置超时时间的方法，设置锁并返回的 lock 有可能不是 true 或 false，而是null。

Boolean lock = redisTemplate.opsForValue().setIfAbsent("redisTemplateTest锁住了", "value", 10, TimeUnit.SECONDS);

从上图我们可以看出虽然生成了锁，但是返回的 lock 却是 null ，这就会影响我们下面的代码运行。
下面我先说一下可能的产生原因和解决办法，之后再详细说一下原理。

2.产生原因及解决办法

最直接的产生原因就是项目启动后缺少了 RedisConnectionFactory 这个bean，导致这一情况的发生有可能是引用了以下的jar包：

 		<dependency><groupId>org.redisson</groupId><artifactId>redisson-spring-boot-starter</artifactId><version>3.10.6</version></dependency>

解决办法很简单：

1）换个jar包使用，如使用：

		<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency>

或者该jar包配合 redisson 包共同使用：

 		<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>org.redisson</groupId><artifactId>redisson</artifactId><version>3.10.6</version></dependency>

2）手动加入 RedisConnectionFactory 这个bean：

	@Beanpublic RedisConnectionFactory redisConnectionFactory(){return new LettuceConnectionFactory();}

3.产生的原理

首先我们要对 springboot 自动装配有一定了解，SpringBoot 启动时会加载所有 META-INF 文件夹下的 spring.factories 文件，在其中找到要装配的类。

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org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\\
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org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\\
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org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\\
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org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\\
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org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\\
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org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\\
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org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\\
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org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\\
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org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\\
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org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\\
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org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\\
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org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

这只是众多 spring.factories 的文件中的一个 ， 从上面我们可以看到 spring 自动配置了 RedisAutoConfiguration 这个bean。下面我们展示一下 RedisAutoConfiguration 的源码：

public class RedisAutoConfiguration {public RedisAutoConfiguration() {}@Bean@ConditionalOnMissingBean(name = {"redisTemplate"})public RedisTemplate<Object, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {RedisTemplate<Object, Object> template = new RedisTemplate();template.setConnectionFactory(redisConnectionFactory);return template;}@Bean@ConditionalOnMissingBeanpublic StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {StringRedisTemplate template = new StringRedisTemplate();template.setConnectionFactory(redisConnectionFactory);return template;}
}

从上面的源码中我们可以得知，装配 RedisAutoConfiguration 这个bean 的时候，同时也会装载 redisTemplate 和 StringRedisTemplate 这两个 bean ，并且这两个bean 都是基于 RedisConnectionFactory 去构建的。

下面我们来看一下 RedisConnectionFactory 的结构 ：

从上图我们可以看出 RedisConnectionFactory 作为一个接口，有 JedisConnectionFactory 和 LettuceConnectionFactory 这两个实现类。

从上面的所有信息中我们可以得知，我们所使用的 redisTemplate 和 StringRedisTemplate 是通过 JedisConnectionFactory 和 LettuceConnectionFactory 这两个实现类来构建的。

下面我们验证一下该结论：

首先我们只引用 spring-boot-starter-data-redis jar包：

		<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency>

从上图可以看出确实是我们推论的 redisTemplate 和 StringRedisTemplate 是通过 LettuceConnectionFactory 来构建的。

我们可以尝试在启动项目的时候打印 spring 容器中的所有 bean 来看一下，以上 redis 的 bean 是否存在。

@SpringBootApplication
public class ApplicationStarter {public static void main(String[] args) {//1.返回我们IOC容器ConfigurableApplicationContext run = SpringApplication.run(ApplicationStarter.class, args);//2.查看容器里面的组件String[] names = run.getBeanDefinitionNames();for (String name : names) {System.out.println(name);}}}

从上图可以看出理应存在的 bean 全部都已经生成完毕，致此，redisTemplate 正常的使用已经说明完毕了。

那么接下来让我们来演示一下为什么获取到了锁还会产生 lock = null 这种情况：

下面我们使用一下 redisson-spring-boot-starter 这个jar包：

 		<dependency><groupId>org.redisson</groupId><artifactId>redisson-spring-boot-starter</artifactId><version>3.10.6</version></dependency>

从上图我们可以看到该jar包配置了 RedissonAutoConfiguration 这个新的 bean 。那么让我们看一下 RedissonAutoConfiguration 的源码：

public class RedissonAutoConfiguration {@Autowiredprivate RedissonProperties redissonProperties;@Autowiredprivate RedisProperties redisProperties;@Autowiredprivate ApplicationContext ctx;public RedissonAutoConfiguration() {}@Bean@ConditionalOnMissingBean(name = {"redisTemplate"})public RedisTemplate<Object, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) {RedisTemplate<Object, Object> template = new RedisTemplate();template.setConnectionFactory(redisConnectionFactory);return template;}@Bean@ConditionalOnMissingBean({StringRedisTemplate.class})public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory) {StringRedisTemplate template = new StringRedisTemplate();template.setConnectionFactory(redisConnectionFactory);return template;}@Bean@ConditionalOnMissingBean({RedisConnectionFactory.class})public RedissonConnectionFactory redissonConnectionFactory(RedissonClient redisson) {return new RedissonConnectionFactory(redisson);}@Bean(destroyMethod = "shutdown")@ConditionalOnMissingBean({RedissonClient.class})public RedissonClient redisson() throws IOException {Config config = null;Method clusterMethod = ReflectionUtils.findMethod(RedisProperties.class, "getCluster");Method timeoutMethod = ReflectionUtils.findMethod(RedisProperties.class, "getTimeout");Object timeoutValue = ReflectionUtils.invokeMethod(timeoutMethod, this.redisProperties);int timeout;Method nodesMethod;if (null == timeoutValue) {timeout = 0;} else if (!(timeoutValue instanceof Integer)) {nodesMethod = ReflectionUtils.findMethod(timeoutValue.getClass(), "toMillis");timeout = ((Long)ReflectionUtils.invokeMethod(nodesMethod, timeoutValue)).intValue();} else {timeout = (Integer)timeoutValue;}if (this.redissonProperties.getConfig() != null) {try {InputStream is = this.getConfigStream();config = Config.fromJSON(is);} catch (IOException var11) {try {InputStream is = this.getConfigStream();config = Config.fromYAML(is);} catch (IOException var10) {throw new IllegalArgumentException("Can't parse config", var10);}}} else if (this.redisProperties.getSentinel() != null) {nodesMethod = ReflectionUtils.findMethod(Sentinel.class, "getNodes");Object nodesValue = ReflectionUtils.invokeMethod(nodesMethod, this.redisProperties.getSentinel());String[] nodes;if (nodesValue instanceof String) {nodes = this.convert(Arrays.asList(((String)nodesValue).split(",")));} else {nodes = this.convert((List)nodesValue);}config = new Config();((SentinelServersConfig)config.useSentinelServers().setMasterName(this.redisProperties.getSentinel().getMaster()).addSentinelAddress(nodes).setDatabase(this.redisProperties.getDatabase()).setConnectTimeout(timeout)).setPassword(this.redisProperties.getPassword());} else {Method method;if (clusterMethod != null && ReflectionUtils.invokeMethod(clusterMethod, this.redisProperties) != null) {Object clusterObject = ReflectionUtils.invokeMethod(clusterMethod, this.redisProperties);method = ReflectionUtils.findMethod(clusterObject.getClass(), "getNodes");List<String> nodesObject = (List)ReflectionUtils.invokeMethod(method, clusterObject);String[] nodes = this.convert(nodesObject);config = new Config();((ClusterServersConfig)config.useClusterServers().addNodeAddress(nodes).setConnectTimeout(timeout)).setPassword(this.redisProperties.getPassword());} else {config = new Config();String prefix = "redis://";method = ReflectionUtils.findMethod(RedisProperties.class, "isSsl");if (method != null && (Boolean)ReflectionUtils.invokeMethod(method, this.redisProperties)) {prefix = "rediss://";}((SingleServerConfig)config.useSingleServer().setAddress(prefix + this.redisProperties.getHost() + ":" + this.redisProperties.getPort()).setConnectTimeout(timeout)).setDatabase(this.redisProperties.getDatabase()).setPassword(this.redisProperties.getPassword());}}return Redisson.create(config);}private String[] convert(List<String> nodesObject) {List<String> nodes = new ArrayList(nodesObject.size());Iterator var3 = nodesObject.iterator();while(true) {while(var3.hasNext()) {String node = (String)var3.next();if (!node.startsWith("redis://") && !node.startsWith("rediss://")) {nodes.add("redis://" + node);} else {nodes.add(node);}}return (String[])nodes.toArray(new String[nodes.size()]);}}private InputStream getConfigStream() throws IOException {Resource resource = this.ctx.getResource(this.redissonProperties.getConfig());InputStream is = resource.getInputStream();return is;}
}

从以上代码可以看出 RedissonAutoConfiguration 是先构建 RedissonClient ，之后通过 RedissonClient 构建 RedissonConnectionFactory ，然后通过 RedissonConnectionFactory 构建 redisTemplate 和 StringRedisTemplate 。和之前构建 redisTemplate 的不同主要在于使用了不同的 RedisConnectionFactory 实现类：

我们同样打印一下 spring 容器中的 bean 看一下：

从上文两种jar包的对比，我们可以得知两种方式获取 redisTemplate 的区别正是在于 RedisConnectionFactory 的实现类不同，而这也是导致 lock = null 的原因所在。 redisson 底层调用了大量的 netty 包，该jar包自带的 RedissonConnectionFactory 影响了之前的返回逻辑，下面我们简单验证一下推论：

从上图可以看出该jar包确实是通过 RedissonConnectionFactory 构建 redisTemplate ，并且返回的 lock 为 null 。

下面我们手动加入 RedisConnectionFactory 这个bean进行对照看下：

	@Beanpublic RedisConnectionFactory redisConnectionFactory(){return new LettuceConnectionFactory();}

从上面的对比可以看出我们的推论完全是正确的， redisson-spring-boot-starter 这个jar包的 RedissonConnectionFactory 影响了原本的判断，导致返回 lock=null 这种现象。

由于 Redisson 里面运用了大量的回调方法、匿名表达式、异步操作等难以debug的方法，所以我这里只在表层进行了问题的排查与解决，如果有哪位大佬具体排查出在代码运行中具体是什么原因导致了使用 RedissonConnectionFactory 返回 lock=null 这种现象。使用它与使用 LettuceConnectionFactory 的返回差异具体体现在哪里的话麻烦告知一声。

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