@InterfaceAudience.Public @InterfaceStability.Unstable

Package org.apache.hadoop.util.functional

Support for functional programming within the Hadoop APIs.

See: Description

Interface Summary

Interface	Description
BiFunctionRaisingIOE<T,U,R>	Function of arity 2 which may raise an IOException.
CallableRaisingIOE<R>	This is a callable which only raises an IOException.
ConsumerRaisingIOE<T>	Version of java.util.function.Consumer which raises exceptions.
Function4RaisingIOE<I1,I2,I3,I4,R>	Function of arity 4 which may raise an IOException.
FunctionRaisingIOE<T,R>	Function of arity 1 which may raise an IOException.
InvocationRaisingIOE	This is a lambda-expression which may raises an IOException.
TaskPool.FailureTask<I,E extends Exception>	Callback invoked on a failure.
TaskPool.Submitter	Interface to whatever lets us submit tasks.
TaskPool.Task<I,E extends Exception>	Callback invoked to process an item.

Class Summary

Class	Description
CloseableTaskPoolSubmitter	A task submitter which is closeable, and whose close() call shuts down the pool.
CommonCallableSupplier<T>	A bridge from Callable to Supplier; catching exceptions raised by the callable and wrapping them as appropriate.
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.
RemoteIterators.WrappingRemoteIterator<S,T>	Wrapper of another remote iterator; IOStatistics and Closeable methods are passed down if implemented.
TaskPool.Builder<I>	Builder for task execution.

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.