java-stream

Java 8 Streams - Nested Maps to List

由 ∥☆過路亽．° 提交于 2019-12-08 06:01:53
问题 firstlist .stream() .map( x -> { return secondList .stream() .map( y -> { //return a string } ) .collect(Collectors.toList()) // "Output" I need } ) .//Get the "Output" here I have two list. the item in first list have to compared with second list and new list have to built. Sample Input List 1 : [ { "id" ; 3, "names" : ["test","test2"] }] List 2 : [ {"name": :"test" , "age" :3}] Output: List 3 : [ {"id" : 3, "name" : "test", "age" :3} ] P.S: The names in first list should be checked against

How to use Streams api peek() function and make it work?

由 ◇◆丶佛笑我妖孽 提交于 2019-12-08 05:43:30
问题 According to this question, peek() is lazy it means we should somehow activate it. In fact, to activate it to print something out to the console I tried this : Stream<String> ss = Stream.of("Hi","Hello","Halo","Hacker News"); ss.parallel().peek(System.out::println); System.out.println("lol"); // I wrote this line to print sth out to terminal to wake peek method up But that doesn't work and the output is : lol Thus, how can I make the peek function actually work? If there is no way to that so

Efficiently Process file comparison using Parallel Stream

由 强颜欢笑 提交于 2019-12-08 05:33:39
问题 So, I have multiple txt files, say txt1,txt2,... and each line has some text between 4 and 22 characters and I have another txt file with similar values, say bigText . The goal is to check all values that are in bigTxt that occur somewhere in any of the txt files and output those values (we're guaranteed that if any line of bigTxt is in any of the txt files, a matching with that line only happens once). The best solution I have so far works, but is slightly inefficient. Basically, it looks

Issue with advanced java 8 stream usage

由 折月煮酒 提交于 2019-12-08 05:07:52
问题 I am trying to use java 8 streams in order to perform a manipulation on a list of Message and Member . A Message is a entity from my domain model. A Message has a sender field and a receiver field of type Member . A Member is the second entity from my domain model. A Member has a collection of sent messages and a collection of received messages. Member JPA entity : @Entity public class Member implements UserDetails { private static final long serialVersionUID = 1L; @Id @GeneratedValue

Will inner parallel streams be processed fully in parallel before considering parallelizing outer stream?

由 廉价感情. 提交于 2019-12-08 04:50:09
问题 From this link, I only partially understood that, at least at some point, there was a problem with java nested parallel streams. However, I couldn't deduce the answer to the following question: Let's say I have an outer srtream and an inner stream, both of which are using parallel stream. It turns out, according to my calculations, that it'll be more performant (due to data locality, ie caching in L1/L2/L3 CPU caches) if the inner stream is done fully in parallel first, and then (if and only

Parallel message unmarshalling from a token delimited input stream with Java8 stream API

由 六眼飞鱼酱① 提交于 2019-12-08 04:48:33
Is it possible with Java8 stream API to create interface like Message pullNext() plumbed on top of a delimited input stream with the logical steps as below? Delimited tokens are read from the character input stream Tokens fed to parallel unmarshaller (one token -> one Message) Messages are reordered back to retain the original incoming order Messages are pullable with aforementioned pullNext() Somewhat a disruptor with unmarshal stage served by concurrent pool. Similar to this, maybe (implementation of stash on top of InputStream is the one to sort out): Iterable<String> stash = Iterables

Java 8 map each field value of a List to another similar List

由 痞子三分冷 提交于 2019-12-08 04:30:21
问题 I have 2 List of objects: List<User> List<UserResource> For User class: public class User { private int id; private String name; private String address; **SETTERS & GETTERS** } For UserResource class: public class UserResource { private String name; private String address; **SETTERS & GETTERS** } My List<User> has data and i want to map value in name and address to UserResource 's name and address , using java 8 stream and lambda, but i not sure how to do it. Search online for quite sometime

Java - Lambda filter criteria, to ignore adding to map

由 99封情书 提交于 2019-12-08 02:45:15
问题 I have a map of the format (reference to Finding average using Lambda (Double stored as String)) Map<String, Double> averages=mapOfIndicators.values().stream() .flatMap(Collection::stream) .filter(objectDTO -> !objectDTO.getNewIndex().isEmpty()) .collect(Collectors.groupingBy(ObjectDTO::getCountryName, Collectors.mapping(ObjectDTO::getNewIndex, Collectors.averagingDouble(Double::parseDouble)))); I would like to ignore the ignore the entire country mapping even if one of them is newIndex value

Java8 stream operations are cached? [duplicate]

由 孤街醉人 提交于 2019-12-08 02:39:29
问题 This question already has an answer here : Java 8, first processing of a list is slower than the subsequent processing (1 answer) Closed 3 years ago . I ran below sample code in my PC running with Intel(R) Xeon(R) CPU E5-2680 0 @ 2.70GHz (2 CPUs), ~2.7GHz String format = "%7s run taken %6d micro seconds %5d findAny"; // First run long start = System.nanoTime(); int rand = IntStream.range(0, 100000).parallel().findAny().getAsInt(); long end = System.nanoTime(); System.out.println(String.format

Based on condition set object value and return boolean using java 8 streams

由 江枫思渺然 提交于 2019-12-08 02:27:26
问题 I have nested list and am able to set isMatched and department.setMatchedStatus(true) when if condition is true. boolean isMatched = false; for (Employee employee: company.getEmployees()) { for (Department department: employee.getDepartments()) { if(departmentList.contains(department.getDepartmentName())){ isMatched = true; department.setMatchedStatus(true); } } } return isMatched; Would like to achieve the same using java 8 streams, which i tried using below code, but couldn't return boolean
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