@Override
    public Mono<byte[]> getData(final String key) {
        return isExist(key).mapNotNull(exist -> {
            if (exist) {
                return this.mainCache.get(key).asMap().get(key);
            }
            return null;
        });
    }
Get data with the key.

@param key the cache key
@return the data
shenyu-plugin/shenyu-plugin-cache/shenyu-plugin-cache-memory/src/main/java/org/apache/shenyu/plugin/cache/memory/MemoryCache.java