在Spring中有一个类CachingUserDetailsService实现了UserDetailsService接口，该类使用静态代理模式为UserDetailsService提供缓存功能。该类源码如下：

CachingUserDetailsService.java

public class CachingUserDetailsService implements UserDetailsService {
    private UserCache userCache = new NullUserCache();
    private final UserDetailsService delegate;

    CachingUserDetailsService(UserDetailsService delegate) {
        this.delegate = delegate;
    }

    public UserCache getUserCache() {
        return this.userCache;
    }

    public void setUserCache(UserCache userCache) {
        this.userCache = userCache;
    }

    public UserDetails loadUserByUsername(String username) {
        UserDetails user = this.userCache.getUserFromCache(username);
        if (user == null) {
            user = this.delegate.loadUserByUsername(username);
        }

        Assert.notNull(user, "UserDetailsService " + this.delegate + " returned null for username " + username + ". This is an interface contract violation");
        this.userCache.putUserInCache(user);
        return user;
    }
}

CachingUserDetailsService默认的userCache属性值为new NullUserCache()，该对象并未实现缓存。因为我打算使用EhCache来缓存UserDetails，所以需要使用Spring的EhCacheBasedUserCache类，该类是UserCache接口的实现类，主要是缓存操作。

缓存UserDetails到Ehcache的具体实现如下：

ehcache.xml

<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd">
    <!-- 磁盘缓存位置 -->
    <diskStore path="java.io.tmpdir" />

    <cache name="userCache"
           maxElementsInMemory="0"
           eternal="true"
           overflowToDisk="true"
           diskPersistent="true"
           memoryStoreEvictionPolicy="LRU">
    </cache>
</ehcache>

UserDetailsCacheConfig.java

@Slf4j
@Configuration
public class UserDetailsCacheConfig {
    @Autowired
    private CustomUserDetailsService customUserDetailsService;

    @Bean
    public UserCache userCache(){
        try {
            EhCacheBasedUserCache userCache = new EhCacheBasedUserCache();
            val cacheManager = CacheManager.getInstance();
            val cache = cacheManager.getCache("userCache");
            userCache.setCache(cache);
            return userCache;
        } catch (Exception e) {
            e.printStackTrace();
            log.error(e.getMessage());
        }
        return null;
    }

    @Bean
    public UserDetailsService userDetailsService(){
        Constructor<CachingUserDetailsService> ctor = null;
        try {
            ctor = CachingUserDetailsService.class.getDeclaredConstructor(UserDetailsService.class);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        Assert.notNull(ctor, "CachingUserDetailsService constructor is null");
        ctor.setAccessible(true);

        CachingUserDetailsService cachingUserDetailsService = BeanUtils.instantiateClass(ctor, customUserDetailsService);
        cachingUserDetailsService.setUserCache(userCache());
        return cachingUserDetailsService;
    }
}

使用

@Autowired
private UserDetailsService userDetailsService;

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