Java 8 Parallel ImageStreamGang Example (Part 3)

Transcription

1 Java 8 Parallel ImageStreamGang Example (Part 3) Douglas C. Schmidt d.schmidt@vanderbilt.edu Professor of Computer Science Institute for Software Integrated Systems Vanderbilt University Nashville, Tennessee, USA

2 Learning Objectives in this Part of the Lesson Recognize the structure/functionality of the ImageStreamGang app Know how Java 8 parallel streams are applied to the ImageStreamGang app Understand the parallel streams implementation of ImageStreamGang List<Image> filteredimages = urls See github.com/douglascraigschmidt/livelessons/blob/master/imagestreamgang 2

3 Implementing a Parallel Stream in ImageStreamGang 3

4 See imagestreamgang/streams/imagestreamparallel.java 4

5 Get a list of URLs 5

6 Convert a collection into a parallel stream 6

7 Return an output stream consisting of the URLs in the input stream that are not already cached See docs.oracle.com/javase/8/docs/api/java/util/stream/stream.html#filter 7

8 Return an output stream consisting of the URLs in the input stream that are not already cached # of output stream elements will 8be <= # of input stream elements

9 boolean urlcached(url url) { return mfilters.stream().filter(filter -> urlcached(url, filter.getname())).count() > 0; See imagestreamgang/streams/imagestreamgang.java 9

10 boolean urlcached(url url, String filtername) { File file = new File(getPath(), filtername); File imagefile = new File(file, getnameforurl(url)); return imagefile.exists(); See imagestreamgang/streams/imagestreamgang.java 10

11 Return an output stream consisting of the images that were downloaded from the URLs in the input stream See docs.oracle.com/javase/8/docs/api/java/util/stream/stream.html#map 11

12 Return an output stream consisting of the images that were downloaded from the URLs in the input stream # of output stream elements must match 12 the # of input stream elements

13 Image blockingdownload (URL url) { return BlockingTask.callInManagedBlock (() -> downloadimage(url)); See imagestreamgang/streams/imagestreamparallel.java 13

14 Image blockingdownload (URL url) { return BlockingTask.callInManagedBlock (() -> downloadimage(url)); We covered what BlockingTask.callInManagedBlock() 14 earlier in this course

15 Return an output stream containing the results of applying a list of filters to each image in the input stream & storing the results in the file system See docs.oracle.com/javase/8/docs/api/java/util/stream/stream.html#flatmap 15

16 Return an output stream containing the results of applying a list of filters to each image in the input stream & storing the results in the file system # of output stream elements may differ 16 from the # of input stream elements

17 Stream<Image> applyfilters (Image image) { return mfilters.map(filter -> makefilterwithimage (filter, image).run()) See imagestreamgang/streams/imagestreamparallel.java 17

18 Terminal operation triggers stream processing & yields a list result See docs.oracle.com/javase/8/docs/api/java/util/stream/stream.html#collect 18

19 Terminal operation triggers stream processing & yields a list result collect() is a reduction operation that 19 combines elements into one result

20 Writes out the # of images downloaded, filtered, & stored 20

21 End of Java 8 Parallel ImageStreamGang Example (Part 3) 21