Spring Cache Redis模糊清除时使用scan

使用 spring-cache-redis 的缓存注解 CacheEvict时，如果使用了allEntries = true 的批量清除开关，默认的处理方式是使用 keys 命令来批量查找key，如何换成 scan 呢？

观察项目中使用的 spring-data-redis 包，如果大于 2.6.x ，可以使用如下方式：

@Bean
    public CacheManager cacheManager(RedisConnectionFactory redisConnectionFactory, CacheProperties cacheProperties) {
        Map configMap = new HashMap<>(16);
        cacheProperties.getTtls()
                .forEach((k, v) -> configMap.put(k, RedisCacheConfiguration.defaultCacheConfig()
                        .computePrefixWith(name -> name + SEPARATOR)
                        .serializeKeysWith(SerializationPair.fromSerializer(RedisSerializer.string()))
                        .serializeValuesWith(SerializationPair.fromSerializer(cacheSerializer))
                        .entryTtl(Duration.ofSeconds(v))));
        return new RedisCacheManager(
                RedisCacheWriter.nonLockingRedisCacheWriter(redisConnectionFactory, BatchStrategies.scan(cacheProperties.getScanBatchSize())),
                RedisCacheConfiguration.defaultCacheConfig()
                        .computePrefixWith(name -> name + SEPARATOR)
                        .serializeKeysWith(SerializationPair.fromSerializer(RedisSerializer.string()))
                        .serializeValuesWith(SerializationPair.fromSerializer(cacheSerializer))
                        .entryTtl(Duration.ofSeconds(cacheProperties.getDefaultTtl())), configMap);
    }

这段代码里我声明了项目中用来处理缓存配置的 CacheManager ，通常这个manager需要自定义声明，其中的关键就在于声明manager中需使用到的 RedisCacheWriter 的这句

RedisCacheWriter.nonLockingRedisCacheWriter(redisConnectionFactory, BatchStrategies.scan(cacheProperties.getScanBatchSize()))
// 如果参数没有指定Strategy是scan，默认便是key

如果小于 2.6.x 稍微麻烦一些，同样在上面声明cacheManager的位置配置，此时需要引入一个自定义的RedisCacheWriter ：

import org.springframework.data.redis.cache.CacheStatistics;
import org.springframework.data.redis.cache.CacheStatisticsCollector;
import org.springframework.data.redis.cache.RedisCacheWriter;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.Cursor;
import org.springframework.data.redis.core.ScanOptions;
import org.springframework.lang.NonNull;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

import java.time.Duration;
import java.util.HashSet;
import java.util.Set;

/**
 * 自定义redis缓存writer，使用scan替代key*
 * 

 * 简化了部分代码，不支持开启操作锁和请求统计，要用时再调整代码
 */
public class CustomizedCacheWriter implements RedisCacheWriter {
    private final RedisCacheWriter defaultWriter;
    private final RedisConnectionFactory connectionFactory;
    private final CacheProperties cacheProperties;

    public CustomizedCacheWriter(@NonNull RedisCacheWriter defaultWriter, @NonNull RedisConnectionFactory connectionFactory) {
        this.defaultWriter = defaultWriter;
        this.connectionFactory = connectionFactory;
    }

    @Override
    public void put(String name, byte[] key, byte[] value, @Nullable Duration ttl) {
        defaultWriter.put(name, key, value, ttl);
    }

    @Override
    @Nullable
    public byte[] get(String name, byte[] key) {
        return defaultWriter.get(name, key);
    }

    @Override
    @Nullable
    public byte[] putIfAbsent(String name, byte[] key, byte[] value, @Nullable Duration ttl) {
        return defaultWriter.putIfAbsent(name, key, value, ttl);
    }

    @Override
    public void remove(String name, byte[] key) {
        defaultWriter.remove(name, key);
    }

    @Override
    public void clean(String name, byte[] pattern) {
        Assert.notNull(name, "Name must not be null!");
        Assert.notNull(pattern, "Pattern must not be null!");

        try (RedisConnection connection = connectionFactory.getConnection()) {
            Cursor cursor = connection.scan(
                    ScanOptions.scanOptions().count(1000).match(new String(pattern)).build());
            Set ks = new HashSet<>();
            while (cursor.hasNext()) {
                ks.add(cursor.next());
            }
            byte[][] keys = ks.toArray(new byte[0][]);
            //            byte[][] keys = Optional.ofNullable(connection.keys(pattern)).orElse(Collections.emptySet()).toArray(new byte[0][]);
            if (keys.length > 0) {
                connection.del(keys);
            }
        }
    }

    @Override
    public void clearStatistics(String name) {
        defaultWriter.clearStatistics(name);
    }

    @Override
    public RedisCacheWriter withStatisticsCollector(CacheStatisticsCollector cacheStatisticsCollector) {
        return defaultWriter.withStatisticsCollector(cacheStatisticsCollector);
    }

    @Override
    public CacheStatistics getCacheStatistics(String cacheName) {
        return defaultWriter.getCacheStatistics(cacheName);
    }
}

上面声明了一个自定义的RedisCacheWriter 实现类，其实是包装了默认的RedisCacheWriter 完成除了clean方法之外的所有事情，而clean方法中使用了 scan 替代了原本的 keys 处理方式。

由于项目中没有使用到处理锁和统计功能，clean方法内容简化了不少，如果有用到锁和统计需要另外处理。

最后在声明manager处调整自定义writer的使用：

RedisCacheWriter cacheWriter = RedisCacheWriter.nonLockingRedisCacheWriter(redisConnectionFactory);
return new RedisCacheManager(new CustomizedCacheWriter(cacheWriter, redisConnectionFactory),
                RedisCacheConfiguration.defaultCacheConfig()
                        .computePrefixWith(name -> name + SEPARATOR)
                        .serializeKeysWith(SerializationPair.fromSerializer(RedisSerializer.string()))
                        .serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(cacheSerializer))
                        .entryTtl(Duration.ofSeconds(cacheProperties.getDefaultTtl())), configMap);