Package org.apache.commons.lang3.stream

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

    • Constructor Summary

      Constructors 
      Constructor Description
      Streams()  

    • Constructor Detail

      • Streams

        public Streams()

    • Method Detail

      • stream

        public static <O> Streams.FailableStream<O> stream​(java.util.Collection<O> 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:
        O - The streams element type.
        Parameters:
        stream - The stream, which is being converted.
        Returns:
        The Streams.FailableStream, which has been created by converting the stream.

      • stream

        public static <O> Streams.FailableStream<O> stream​(java.util.stream.Stream<O> 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:
        O - 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 <O> java.util.stream.Collector<O,​?,​O[]> toArray​(java.lang.Class<O> pElementType)
        Returns a Collector that accumulates the input elements into a new array.
        Type Parameters:
        O - 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