@InterfaceAudience.Public @InterfaceStability.Unstable

Package org.apache.hadoop.util.functional

Support for functional programming within the Hadoop APIs.

See: Description

Class Summary

Class	Description
CloseableTaskPoolSubmitter	A task submitter which is closeable, and whose close() call shuts down the pool.
FutureIO	Future IO Helper methods.
RemoteIterators	A set of remote iterators supporting transformation and filtering, with IOStatisticsSource passthrough, and of conversions of the iterators to lists/arrays and of performing actions on the values.

Package org.apache.hadoop.util.functional Description

Support for functional programming within the Hadoop APIs. Much of this is needed simply to cope with Java's checked exceptions and the fact that the java.util.function can only throw runtime exceptions.

Pretty much all the Hadoop FS APIs raise IOExceptions, hence the need for these classes. If Java had made a different decision about the nature of exceptions, life would be better.

Do note that the RemoteIterators iterators go beyond that of the java ones, in terms of declaring themselves Closeable and implementors of IOStatisticsSource; a chain of wrapped iterators can supply statistics of the inner iterators, and encourage close() to be called after use.