Java 8 CompletableFutures

ImageStreamGang Example (Part 1)

Douglas C. Schmidtd.schmidt@vanderbilt.edu

www.dre.vanderbilt.edu/~schmidt

Professor of Computer Science

Institute for Software

Integrated Systems

Vanderbilt University

Nashville, Tennessee, USA

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Learning Objectives in this Part of the Lesson• Understand the design of the Java 8 completable future

version of the ImageStreamGang app

SocketSocket

List of URLs to Download

…

List of Filters to Apply

Persistent

Data Store

See github.com/douglascraigschmidt/LiveLessons/tree/master/ImageStreamGang

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Overview of the CompletableFutures ImageStreamGang

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• ImageStreamGang applies completable future to optimize performance

See github.com/douglascraigschmidt/LiveLessons/tree/master/ImageStreamGang

Overview of Completable Futures ImageStreamGang

Socket

Socket

Persistent

Data Store

List of Filters to Apply

List of URLs to Download

…

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• ImageStreamGang applies completable future to optimize performance

• Ignore cached images

• Download non-cached images

• Apply list of filters to each image

• Store filtered images in the file system

• Display images to the user

Overview of Completable Futures ImageStreamGang

Socket

Socket

Persistent

Data Store

List of Filters to Apply

List of URLs to Download

…

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• The behaviors in this pipeline differ from the earlier parallel streams variant

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

List of URLs to Download

…

collect(toList())

…

filter(not(this::urlCached))

map(this::downloadImage)

flatMap(this::applyFilters)

Parallel Streams Completable Futures

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• The behaviors in this pipeline differ from the earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

List of URLs to Download

…

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• The behaviors in this pipeline differ from the earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

• Download non-cached imagesasynchronously

Overview of Completable Futures ImageStreamGangList of URLs to Download

…

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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List of URLs to Download

…• The behaviors in this pipeline differ from the

earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

• Download non-cached imagesasynchronously

• As downloads complete asynchronously apply a list of filters & store filtered images in file system

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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List of URLs to Download

…• The behaviors in this pipeline differ from the

earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

• Download non-cached imagesasynchronously

• As downloads complete asynchronously apply a list of filters & store filtered images in file system

• Trigger all the stream processing torun asynchronously

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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List of URLs to Download

…• The behaviors in this pipeline differ from the

earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

• Download non-cached imagesasynchronously

• As downloads complete asynchronously apply a list of filters & store filtered images in file system

• Trigger all the stream processing torun asynchronously

• Get results of asynchronous computations

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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• The behaviors in this pipeline differ from the earlier parallel streams variant, e.g.

• Ignore cached images asynchronously

• Download non-cached imagesasynchronously

• As downloads complete asynchronously apply a list of filters & store filtered images in file system

• Trigger all the stream processing torun asynchronously

• Get results of asynchronous computations

• Ultimately display images to user

Overview of Completable Futures ImageStreamGangList of URLs to Download

…

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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List of URLs to Download

…• Combining completable futures & streams

helps to close the gap between the design intent & the implementation

Overview of Completable Futures ImageStreamGang

map(this::downloadImageAsync)

thenAccept(this::log)

flatMap(this::applyFiltersAsync)

collect(toFuture())

map(this::checkUrlCachedAsync)

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End of Java 8 CompletableFutures ImageStreamGang

Example (Part 1)