java-stream

I have some large-ish text files that I want to process by grouping its lines. I tried to use the new streaming features, like return FileUtils.readLines(...) .parallelStream() .map(...) .collect(groupingBy(pair -> pair[0])); The problem is that, AFAIK, this generates a Map. Is there any way to have high level code like the one above that generates, for example, a Stream of Entries? UPDATE : What I'm looking for is something like python's itertools.groupby . My files are already sorted (by pair[0]), I just want to load the groups one by one. I already have an iterative solution. I'm just

I was trying to filter Entries in HashMap using Streams API, but stuck in last method call Collectors.toMap . So, I don't have clue to implemement toMap method public void filterStudents(Map<Integer, Student> studentsMap){ HashMap<Integer, Student> filteredStudentsMap = studentsMap.entrySet().stream(). filter(s -> s.getValue().getAddress().equalsIgnoreCase("delhi")). collect(Collectors.toMap(k , v)); } public class Student { private int id; private String firstName; private String lastName; private String address; ... } Any Suggestions? Just generate the output Map out of the key and value of

I have hundreds of large (6GB) gziped log files that I'm reading using GZIPInputStream s that I wish to parse. Suppose each one has the format: Start of log entry 1 ...some log details ...some log details ...some log details Start of log entry 2 ...some log details ...some log details ...some log details Start of log entry 3 ...some log details ...some log details ...some log details I'm streaming the gziped file contents line by line through BufferedReader.lines() . The stream looks like: [ "Start of log entry 1", " ...some log details", " ...some log details", " ...some log details", "Start

Similar to my previous question here , the User objects I have are these new User("ayush","admin",23) new User("ashish","guest",19) new User("ashish","admin",20) new User("garima","guest",29) new User("garima","super",45) new User("garima","guest",19) Now I am trying to get the name to varying ages trend for these users. But I need to filter them above a threshold age. I could get the trend using Map<String, List<Integer>> userNameAndAgeTrend = users.stream().collect(Collectors.groupingBy(user-> user.getName(), Collectors.mapping(u-> u.getAge(), toList()))); this gives me {ashish=[19, 20],

Is there a way to receive a Stream<String> stream out of a BufferedReader reader such that each string in stream represents one line of reader with the additional condition that stream is provided directly (before reader read everything)? I want to process the data of stream parallel to getting them from reader to save time. Edit: I want to process the data parallel to reading. I don't want to process different lines parallel. They should be processed in order. Let's make an example on how I want to save time. Let's say our reader will present 100 lines to us. It takes 2 ms to read one line

After tomcat upgrade from 8.5.6 to 8.5.28 parallel stream stopped supplying Threads with contextClassLoader: Because of it Warmer::run can't load classes in it. warmers.parallelStream().forEach(Warmer::run); Do you have any ideas what Tomcat was supplying for contextClassLoaders for new Threads? ParallelStream uses ForkJoinPool in newest Tomcat. Common ForkJoin pool is problematic and could be responsible for memory leaks and for applications being able to load classes and resources from other contexts/applications (potential security leak if your tomcat is multi tenant). See this Tomcat

I'm attempting to extend Java 8's Stream implementation. I have this interface: public interface StreamStuff<T> extends Stream<T> { Stream<T> delegate(); default Stream<T> biggerThanFour() { return delegate().filter(i -> ((Double)i > 4)); } } And in my main method: int arr [] = {1,2,3,4,5,6}; Object array [] = ((StreamStuff)Arrays .stream(arr)) .biggerThanFour() .toArray(); I'm trying to cast the Stream, to my interface StreamStuff, and use my method. Im getting the following error: Exception in thread "main" java.lang.ClassCastException: java.util.stream.IntPipeline$Head cannot be cast to

I have a method that returns a stream that is generated from a custom spliterator; the spliterator is not tread safe. Since the spliterator is not tread safe, and it maintains state, I want to prevent it from running in parallel. Is there a way to prevent the returned stream from running in parallel? I have not been able to find any documentation or examples that do this. I did find a sequential() method on the BaseStream class, but that does not appear to prevent a user from then calling parallel() to get a parallel stream. Parallel stream calls trySplit() method of your spliterator to split