Many external systems, services or resources aren't transactional (Twitter, RSS, file system etc.) and there is no any ability to mark the data as read. Or there is just need to implement the Enterprise Integration Pattern Idempotent Receiver in some integration solutions. To achieve this goal and store some previous state of the Endpoint before the next interaction with external system, or deal with the next Message, Spring Integration provides the Metadata Store component being an implementation of the org.springframework.integration.metadata.MetadataStore interface with a general key-value contract. The Metadata Store is designed to store various types of generic meta-data (e.g., published date of the last feed entry that has been processed) to help components such as the Feed adapter deal with duplicates. If a component is not directly provided with a reference to a MetadataStore, the algorithm for locating a metadata store is as follows: First, look for a bean with id metadataStore in the ApplicationContext. If one is found then it will be used, otherwise it will create a new instance of SimpleMetadataStore which is an in-memory implementation that will only persist metadata within the lifecycle of the currently running Application Context. This means that upon restart you may end up with duplicate entries. If you need to persist metadata between Application Context restarts, two persistent MetadataStores are provided by the framework: PropertiesPersistingMetadataStore The PropertiesPersistingMetadataStore is backed by a properties file and a PropertiesPersister. ]]> Alternatively, you can provide your own implementation of the MetadataStore interface (e.g. JdbcMetadataStore) and configure it as a bean in the Application Context. Starting with version 4.0, SimpleMetadataStore, PropertiesPersistingMetadataStore and RedisMetadataStore implement ConcurrentMetadataStore. These provide for atomic updates and can be used across multiple component or application instances.

The Metadata Store is useful for implementing the EIP Idempotent Receiver pattern, when there is need to filter an incoming Message if it has already been processed, and just discard it or perform some other logic on discarding. The following configuration is an example of how to do this: ]]> The value of the idempotent entry may be some expiration date, after which that entry should be removed from Metadata Store by some scheduled reaper. Also see .