Package org.springframework.batch.item

Interface ItemReader<T>

All Known Subinterfaces:
ItemStreamReader<T>, PeekableItemReader<T>, ResourceAwareItemReaderItemStream<T>
All Known Implementing Classes:
AbstractCursorItemReader, AbstractItemCountingItemStreamItemReader, AbstractItemStreamItemReader, AbstractPaginatedDataItemReader, AbstractPagingItemReader, AmqpItemReader, AvroItemReader, BlockingQueueItemReader, CompositeItemReader, FlatFileItemReader, ItemReaderAdapter, IteratorItemReader, JdbcCursorItemReader, JdbcPagingItemReader, JmsItemReader, JpaCursorItemReader, JpaPagingItemReader, JsonItemReader, KafkaItemReader, LdifReader, ListItemReader, MappingLdifReader, MongoCursorItemReader, MongoItemReader, MongoPagingItemReader, MultiResourceItemReader, Neo4jItemReader, RedisItemReader, RepositoryItemReader, ResourcesItemReader, SingleItemPeekableItemReader, StaxEventItemReader, StoredProcedureItemReader, SupplierItemReader, SynchronizedItemReader, SynchronizedItemStreamReader
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface ItemReader<T>
Strategy interface for providing the data.
Implementations are expected to be stateful and will be called multiple times for each batch, with each call to read() returning a different value and finally returning null when all input data is exhausted.
Implementations need not be thread-safe and clients of a ItemReader need to be aware that this is the case.
A richer interface (e.g. with a look ahead or peek) is not feasible because we need to support transactions in an asynchronous batch.
Since:
1.0
Author:
Rob Harrop, Dave Syer, Lucas Ward, Mahmoud Ben Hassine, Taeik Lim

  • Method Summary

    Modifier and Type
    Method
    Description
    T
    read()
    Reads a piece of input data and advance to the next one.

  • Method Details

    • read

      @Nullable T read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException
      Reads a piece of input data and advance to the next one. Implementations must return null at the end of the input data set. In a transactional setting, caller might get the same item twice from successive calls (or otherwise), if the first call was in a transaction that rolled back.
      Returns:
      T the item to be processed or null if the data source is exhausted
      Throws:
      ParseException - if there is a problem parsing the current record (but the next one may still be valid)
      NonTransientResourceException - if there is a fatal exception in the underlying resource. After throwing this exception implementations should endeavour to return null from subsequent calls to read.
      UnexpectedInputException - if there is an uncategorised problem with the input data. Assume potentially transient, so subsequent calls to read might succeed.
      Exception - if an there is a non-specific error.