SpringCache 缓存

## 缓存发展史&注意事项
https://www.csrbobo.com/4b4634eb423d4450a4720546193ff9d0/4b4634eb423d4450a4720546193ff9d0.html

## 本地缓存caffeine简单使用
中文使用说明：jianshu.com/p/9a80c662dac4
wiki：https://github.com/ben-manes/caffeine/wiki

1. 添加maven依赖
```
<dependency>
    <groupId>com.github.ben-manes.caffeine</groupId>
    <artifactId>caffeine</artifactId>
    <version>3.0.4</version>
</dependency>
```
2. 注册到spring中
```java
@Configuration
@EnableCaching
public class CaffeineConfig {
	@Bean
	public CaffeineCache userCache(CacheLoader<Object,Object> hexinCacheLoader){
		Cache<Object, Object> cache = Caffeine.newBuilder()
				 .maximumSize(800)
				 .refreshAfterWrite(10, TimeUnit.SECONDS)
				 .expireAfterWrite(20, TimeUnit.SECONDS)
				 .recordStats()
				 .build(hexinCacheLoader);
		return new CaffeineCache("user", cache);
	}

/**
     * 提供一个默认的cacheManager 多缓存策略使用时只需要指定cacheName
     * @param caffeineCacheList 所有注册的 CaffeineCache
     * @return CacheManager
     */
    @Bean
    public CacheManager cacheManager(List<CaffeineCache> caffeineCacheList) {
        SimpleCacheManager cacheManager = new SimpleCacheManager();
        cacheManager.setCaches(caffeineCacheList);
        return cacheManager;
    }
}
```
3. 使用springCache的注解即可
```
	@Cacheable(cacheNames = "user", unless = "null == #result", key = "#root.methodName +':'+ #user")
    public User get(String user) {
		// ...
	} 
```

## 二级缓存
由于springCache 默认只能分布式缓存和本地缓存二选一，有二级缓存需求的可以看看 jetCache
https://github.com/alibaba/jetcache/wiki/Home_CN