I have the following problem:
I have a method as follows that can take a collection of only upto 500 Names at a time:
public Optional<ResultDTO> executeRequest(final int time, List<Name> names) I have a list 1000+ names and hence I want to partition this list out into sublists of max size 500 using guava
List<List<Name>> nameBatches = Lists.partition(namesList, 500); and pass it to the request to get a list of ResultDTOs. How can I do this in Java8?
You will have to create an IntStream to iterate over the chunks in your list and create sub-lists in a separate mapping step.
int chunkSize = 500; int size = namesList.size(); // calc the number of chunks int chunks = (size - 1) / chunkSize; List<List<Name>> res = IntStream // range over all chunks .range(0, chunks + 1) // create sub-lists for each chunk .mapToObj( n -> namesList.subList(n * chunkSize, Math.min(size, (n + 1) * chunkSize))) // collect from Stream<List<String>> to List<List<String>> .collect(Collectors.toList()); Edit: based on your comment
My main issue is how do I call the executeRequest method for each of the name batches and store the results.
Just add an .map(l -> executeRequest(time, l)) before the collect call, and change the type of res to List<Optional<Object>>
I'm not sure if in the java 8 similar functionality has been provided. Of course you can use foreach with anonymous function but it's more unreadable than in the java 8 with using List.subList().
Solution in the Java 7:
final Integer sizeOfChunk = 3; List<Integer> inputList = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 0); //Guava List<List<Integer>> firstListOfLists = Lists.partition(inputList, sizeOfChunk); //Java 7 List<List<Integer>> secondListOfLists = new ArrayList<List<Integer>>(); for (int i=0; i<inputList.size()-sizeOfChunk; i+=sizeOfChunk) { secondListOfLists.add(inputList.subList(i, i+sizeOfChunk)); } if (inputList.size() % sizeOfChunk != 0) { secondListOfLists.add(inputList.subList(secondListOfLists.size()*sizeOfChunk, inputList.size())); } System.out.println("Guava: " + firstListOfLists); System.out.println("Java 7: " + secondListOfLists); EDIT
After your comment, it will be:
List<Optional<ResultDTO>> results = nameBatches .stream().map(l -> executeRequest(something, l)).collect(Collectors.toList()); 
