org.apache.commons.lang3.stream

Class Streams

java.lang.Object

org.apache.commons.lang3.stream.Streams

public class Streams
extends java.lang.Object

Provides utility functions, and classes for working with the java.util.stream package, or more generally, with Java 8 lambdas. More specifically, it attempts to address the fact that lambdas are supposed not to throw Exceptions, at least not checked Exceptions, AKA instances of Exception. This enforces the use of constructs like:

 
 Consumer<java.lang.reflect.Method> consumer = m -> {
     try {
         m.invoke(o, args);
     } catch (Throwable t) {
         throw Failable.rethrow(t);
     }
 };
 stream.forEach(consumer);
 
 

Using a Streams.FailableStream, this can be rewritten as follows:

 
 Streams.failable(stream).forEach((m) -> m.invoke(o, args));
 
 

Obviously, the second version is much more concise and the spirit of Lambda expressions is met better than in the first version.

Since:

3.11

See Also:

Stream, Failable

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Streams.ArrayCollector<E> A Collector type for arrays.
static class	Streams.FailableStream<T> A reduced, and simplified version of a Stream with failable method signatures.

Constructor Summary

Constructors

Constructor and Description
Streams()

Method Summary

Modifier and Type	Method and Description
static <T> Streams.FailableStream<T>	failableStream(java.util.Collection<T> stream) Converts the given Collection into a Streams.FailableStream.
static <T> Streams.FailableStream<T>	failableStream(java.util.stream.Stream<T> stream) Converts the given stream into a Streams.FailableStream.
static <E> java.util.stream.Stream<E>	instancesOf(java.lang.Class<? super E> clazz, java.util.Collection<? super E> collection) Streams only instances of the give Class in a collection.
static <E> java.util.stream.Stream<E>	nonNull(java.util.Collection<E> collection) Streams the non-null elements of a collection.
static <E> java.util.stream.Stream<E>	nonNull(E... array) Streams the non-null elements of an array.
static <E> java.util.stream.Stream<E>	nonNull(java.util.stream.Stream<E> stream) Streams the non-null elements of a stream.
static <E> java.util.stream.Stream<E>	of(java.util.Collection<E> collection) Delegates to Collection.stream() or returns Stream.empty() if the collection is null.
static <E> java.util.stream.Stream<E>	of(java.util.Enumeration<E> enumeration) Streams the elements of the given enumeration in order.
static <E> java.util.stream.Stream<E>	of(java.lang.Iterable<E> iterable) Creates a stream on the given Iterable.
static <E> java.util.stream.Stream<E>	of(java.util.Iterator<E> iterator) Creates a stream on the given Iterator.
static <T> java.util.stream.Stream<T>	of(T... values) Null-safe version of Stream.of(Object[]).
static <E> Streams.FailableStream<E>	stream(java.util.Collection<E> collection) Deprecated. Use failableStream(Collection).
static <T> Streams.FailableStream<T>	stream(java.util.stream.Stream<T> stream) Deprecated. Use failableStream(Stream).
static <T> java.util.stream.Collector<T,?,T[]>	toArray(java.lang.Class<T> pElementType) Returns a Collector that accumulates the input elements into a new array.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Streams

public Streams()

Method Detail

failableStream

public static <T> Streams.FailableStream<T> failableStream(java.util.Collection<T> stream)

Converts the given Collection into a Streams.FailableStream. This is basically a simplified, reduced version of the Stream class, with the same underlying element stream, except that failable objects, like FailablePredicate, FailableFunction, or FailableConsumer may be applied, instead of Predicate, Function, or Consumer. The idea is to rewrite a code snippet like this:

 
 final List<O> list;
 final Method m;
 final Function<O, String> mapper = (o) -> {
     try {
         return (String) m.invoke(o);
     } catch (Throwable t) {
         throw Failable.rethrow(t);
     }
 };
 final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
 
 

as follows:

 
 final List<O> list;
 final Method m;
 final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
 
 

While the second version may not be quite as efficient (because it depends on the creation of additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the spirit of Lambdas better than the first version.

Type Parameters:

T - The streams element type.

Parameters:

stream - The stream, which is being converted.

Returns:

The Streams.FailableStream, which has been created by converting the stream.

Since:

3.13.0

failableStream

public static <T> Streams.FailableStream<T> failableStream(java.util.stream.Stream<T> stream)

Converts the given stream into a Streams.FailableStream. This is basically a simplified, reduced version of the Stream class, with the same underlying element stream, except that failable objects, like FailablePredicate, FailableFunction, or FailableConsumer may be applied, instead of Predicate, Function, or Consumer. The idea is to rewrite a code snippet like this:

 
 final List<O> list;
 final Method m;
 final Function<O, String> mapper = (o) -> {
     try {
         return (String) m.invoke(o);
     } catch (Throwable t) {
         throw Failable.rethrow(t);
     }
 };
 final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
 
 

as follows:

 
 final List<O> list;
 final Method m;
 final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
 
 

While the second version may not be quite as efficient (because it depends on the creation of additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the spirit of Lambdas better than the first version.

Type Parameters:

T - The streams element type.

Parameters:

stream - The stream, which is being converted.

Returns:

The Streams.FailableStream, which has been created by converting the stream.

Since:

3.13.0

instancesOf

public static <E> java.util.stream.Stream<E> instancesOf(java.lang.Class<? super E> clazz,
                                                         java.util.Collection<? super E> collection)

Streams only instances of the give Class in a collection.

This method shorthand for:

  (Stream<E>) Streams.toStream(collection).filter(collection, SomeClass.class::isInstance);
 

Type Parameters:

E - the type of elements in the collection we want to stream.

Parameters:

clazz - the type of elements in the collection we want to stream.

collection - the collection to stream or null.

Returns:

A non-null stream that only provides instances we want.

Since:

3.13.0

nonNull

public static <E> java.util.stream.Stream<E> nonNull(java.util.Collection<E> collection)

Streams the non-null elements of a collection.

Type Parameters:

E - the type of elements in the collection.

Parameters:

collection - the collection to stream or null.

Returns:

A non-null stream that filters out null elements.

Since:

3.13.0

nonNull

@SafeVarargs
public static <E> java.util.stream.Stream<E> nonNull(E... array)

Streams the non-null elements of an array.

Type Parameters:

E - the type of elements in the collection.

Parameters:

array - the array to stream or null.

Returns:

A non-null stream that filters out null elements.

Since:

3.13.0

nonNull

public static <E> java.util.stream.Stream<E> nonNull(java.util.stream.Stream<E> stream)

Streams the non-null elements of a stream.

Type Parameters:

E - the type of elements in the collection.

Parameters:

stream - the stream to stream or null.

Returns:

A non-null stream that filters out null elements.

Since:

3.13.0

of

public static <E> java.util.stream.Stream<E> of(java.util.Collection<E> collection)

Delegates to Collection.stream() or returns Stream.empty() if the collection is null.

Type Parameters:

E - the type of elements in the collection.

Parameters:

collection - the collection to stream or null.

Returns:

Collection.stream() or Stream.empty() if the collection is null.

Since:

3.13.0

of

public static <E> java.util.stream.Stream<E> of(java.util.Enumeration<E> enumeration)

Streams the elements of the given enumeration in order.

Type Parameters:

E - The enumeration element type.

Parameters:

enumeration - The enumeration to stream.

Returns:

a new stream.

Since:

3.13.0

of

public static <E> java.util.stream.Stream<E> of(java.lang.Iterable<E> iterable)

Creates a stream on the given Iterable.

Type Parameters:

E - the type of elements in the Iterable.

Parameters:

iterable - the Iterable to stream or null.

Returns:

a new Stream or Stream.empty() if the Iterable is null.

Since:

3.13.0

of

public static <E> java.util.stream.Stream<E> of(java.util.Iterator<E> iterator)

Creates a stream on the given Iterator.

Type Parameters:

E - the type of elements in the Iterator.

Parameters:

iterator - the Iterator to stream or null.

Returns:

a new Stream or Stream.empty() if the Iterator is null.

Since:

3.13.0

of

@SafeVarargs
public static <T> java.util.stream.Stream<T> of(T... values)

Null-safe version of Stream.of(Object[]).

Type Parameters:

T - the type of stream elements.

Parameters:

values - the elements of the new stream, may be null.

Returns:

the new stream on values or Stream.empty().

Since:

3.13.0

stream

@Deprecated
public static <E> Streams.FailableStream<E> stream(java.util.Collection<E> collection)

Deprecated. Use failableStream(Collection).

Converts the given Collection into a Streams.FailableStream. This is basically a simplified, reduced version of the Stream class, with the same underlying element stream, except that failable objects, like FailablePredicate, FailableFunction, or FailableConsumer may be applied, instead of Predicate, Function, or Consumer. The idea is to rewrite a code snippet like this:

 
 final List<O> list;
 final Method m;
 final Function<O, String> mapper = (o) -> {
     try {
         return (String) m.invoke(o);
     } catch (Throwable t) {
         throw Failable.rethrow(t);
     }
 };
 final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
 
 

as follows:

 
 final List<O> list;
 final Method m;
 final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
 
 

While the second version may not be quite as efficient (because it depends on the creation of additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the spirit of Lambdas better than the first version.

Type Parameters:

E - The streams element type.

Parameters:

collection - The stream, which is being converted.

Returns:

The Streams.FailableStream, which has been created by converting the stream.

stream

@Deprecated
public static <T> Streams.FailableStream<T> stream(java.util.stream.Stream<T> stream)

Deprecated. Use failableStream(Stream).

Converts the given stream into a Streams.FailableStream. This is basically a simplified, reduced version of the Stream class, with the same underlying element stream, except that failable objects, like FailablePredicate, FailableFunction, or FailableConsumer may be applied, instead of Predicate, Function, or Consumer. The idea is to rewrite a code snippet like this:

 
 final List<O> list;
 final Method m;
 final Function<O, String> mapper = (o) -> {
     try {
         return (String) m.invoke(o);
     } catch (Throwable t) {
         throw Failable.rethrow(t);
     }
 };
 final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
 
 

as follows:

 
 final List<O> list;
 final Method m;
 final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
 
 

While the second version may not be quite as efficient (because it depends on the creation of additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the spirit of Lambdas better than the first version.

Type Parameters:

T - The streams element type.

Parameters:

stream - The stream, which is being converted.

Returns:

The Streams.FailableStream, which has been created by converting the stream.

toArray

public static <T> java.util.stream.Collector<T,?,T[]> toArray(java.lang.Class<T> pElementType)

Returns a Collector that accumulates the input elements into a new array.

Type Parameters:

T - the type of the input elements

Parameters:

pElementType - Type of an element in the array.

Returns:

a Collector which collects all the input elements into an array, in encounter order