redis之Springboot源码解析

Jedis在实现上是直接连接的redis server，如果在多线程环境下是非线程安全的，这个时候只有使用连接池，为每个Jedis实例增加物理连接。

Lettuce的连接是基于Netty的，连接实例（StatefulRedisConnection）可以在多个线程间并发访问，应为StatefulRedisConnection是线程安全的，所以一个连接实例（StatefulRedisConnection）就可以满足多线程环境下的并发访问，当然这个也是可伸缩的设计，一个连接实例不够的情况也可以按需增加连接实例。lettuce主要利用netty实现与redis的同步和异步通信。

@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })
public class 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
	@ConditionalOnMissingBean
	public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory)
			throws UnknownHostException {
		StringRedisTemplate template = new StringRedisTemplate();
		template.setConnectionFactory(redisConnectionFactory);
		return template;
	}
}

LettuceConnectionConfiguration、JedisConnectionConfiguration有个公共功能是创建jedis连接工厂类之JedisConnectionFactory。由于先解析LettuceConnectionConfiguration类，所以两者配置类都满足的前提下，优先通过LettuceConnectionConfiguration创建JedisConnectionFactory。

1.JedisConnectionConfiguration

@ConditionalOnClass({ GenericObjectPool.class, JedisConnection.class, Jedis.class })
class JedisConnectionConfiguration extends RedisConnectionConfiguration {
	@ConditionalOnMissingBean(RedisConnectionFactory.class)
	public JedisConnectionFactory redisConnectionFactory() throws UnknownHostException {
		return createJedisConnectionFactory();
	}
}

JedisConnectionConfiguration发挥作用的前提条件之一是存在Jedis类，该类是通过以下依赖引入的：

 <dependency>
    <groupId>redis.clients</groupId>
    <artifactId>jedis</artifactId>
</dependency>

2.LettuceConnectionConfiguration

@Configuration
@ConditionalOnClass(RedisClient.class)
class LettuceConnectionConfiguration extends RedisConnectionConfiguration {

	@Bean
	@ConditionalOnMissingBean(RedisConnectionFactory.class)
	public LettuceConnectionFactory redisConnectionFactory(ClientResources clientResources)
			throws UnknownHostException {
		LettuceClientConfiguration clientConfig = getLettuceClientConfiguration(clientResources,
				this.properties.getLettuce().getPool());
		return createLettuceConnectionFactory(clientConfig);
	}
}

LettuceConnectionConfiguration配置类发挥作用的前提条件之一是存在Jedis类，该类是通过以下依赖引入的：

 <dependency>
   <groupId>io.lettuce</groupId>
   <artifactId>lettuce-core</artifactId>
   <version>5.1.7.RELEASE</version>
   <scope>compile</scope>
 </dependency>

在SpringBoot项目中spring-boot-starter-data-redis包下默认存在lettuce-core。