my data is like this, my goal is put every unitId and value into a map like this, I already figure out two ways to achieve that, here is my code, and, First one more like write the processing manually, second one uses temporary lists which may not be necessary. Is there any direct or simple way to do this,
Tag: collectors
How can I collect two-dimensional Array into a Map<String, Set>?
I have an array of arrays of two strings. How can I collect the above array into a Map<String, Set<String>> whose key is the first element of each array and the value is a set of second elements of the array? So that I get following map? So far, I found I can classify the first element of each array
How can I use an If-statement inside the Collector?
The output I require is like this : The structure of this output is: Map<String, List<Pair<String, String>>> Where “Versions” is the key of the Map and [(“0.1″,”true”),(“0.2″,”false”),(“0.3″,”true”)] this is the value of the Map. Now, inside the Map we have a List like: List<Pair<String, String>> eg is this : [(“0.1″,”true”),(“0.2″,”false”),(“0.3″,”true”)] Where “0.1”,”0.2″,”0.3″ is the key of the Pair and “true”,”false”,”true”
Custom Collector that cannot work in parallel
I have made a custom collector that uses a MessageDigest to create a hash. In general MessageDigest does not work in parallel. The issue I’m seeing is in the combiner() method. It is not possible to combine two MessageDigest objects. When I return null it seems to work but if I throw an UnsupportedOperationException it fails. What is the typical
Java 8 List from String and List of String
I want to generate a list of strings, comprising id and external ids, from a list of Bean. I got it using the below code, but here I need to do the stream twice. Is there any better way to rewrite this code? Answer Use Stream.concat inside the flatMap operation:
Java Collectors Grouping By
I have an input of integers and I would like to sort all even numbers before all odd ones in ascending order and preserve the odds order. I am pretty sure I can achieve that with collectors and/or downstream collectors, but I am not sure how to do it. I would like to know how can I sort the false
Zipped String from 2 (or more) Strings – “AB” + “YZ” = “AYBZ”
So I am trying to return another String from 2 input sentences zipped together. If the 2 sentences are identical in length it will produce an actual output. If the two input sentences are not identical in length then it will just return an empty string. Here is my code so far but I can’t figure out how to zip
How to extract values from a list of class objects, remove the duplicates and sort alphabetically?
I have a class Tag in java and I am extracting descriptions from a list of Tag objects rawTags to a set (I need to remove duplicate values): but I also want to have the resulting set (or list of unique descriptions) alphabetically ordered. Is there a way how to use TreeSet directly with Collectors or what would be the
Convert a list of integers into a comma-separated string
I was trying to convert a list of Integers into a string of comma-separated integers. Collectors.joining(CharSequence delimiter) – Returns a Collector that concatenates the input elements, separated by the specified delimiter, in encounter order. I am getting an error in line number 8: The method collect(Collector<? super Integer,A,R>) in the type Stream is not applicable for the arguments (Collector<CharSequence,capture#20-of ?,String>)
extract list inside a list as a single list
I’ve a two POJOs, Sample code below Controller class This returns me a list of the list: but what I want is a single list like How can I do that with Java 8 streams? I’ve tried flatMap also, but that doesn’t go well with the Object datatype of entries. Answer Consider a List<String> as a field entries in the