org.springframework.batch.item

Interface ItemReader<T>

All Known Subinterfaces:

ItemStreamReader<T>, PeekableItemReader<T>, ResourceAwareItemReaderItemStream<T>

All Known Implementing Classes:

AbstractCursorItemReader, AbstractItemCountingItemStreamItemReader, AbstractItemStreamItemReader, AbstractNeo4jItemReader, AbstractPaginatedDataItemReader, AbstractPagingItemReader, AmqpItemReader, AvroItemReader, FlatFileItemReader, HibernateCursorItemReader, HibernatePagingItemReader, ItemReaderAdapter, ItemReaderAdapter, IteratorItemReader, JdbcCursorItemReader, JdbcPagingItemReader, JmsItemReader, JpaCursorItemReader, JpaPagingItemReader, JsonItemReader, KafkaItemReader, LdifReader, ListItemReader, MappingLdifReader, MongoItemReader, MultiResourceItemReader, Neo4jItemReader, RepositoryItemReader, ResourcesItemReader, SingleItemPeekableItemReader, StaxEventItemReader, StoredProcedureItemReader, SynchronizedItemStreamReader

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

Method Summary

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

Method Detail

read

@Nullable
T read()
          throws java.lang.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.

java.lang.Exception - if an there is a non-specific error.