我为自己编写了一个实用程序，将列表分解为给定大小的批次。我只是想知道是否已经有任何apache commons util用于此。
public static <T> List<List<T>> getBatches(List<T> collection,int batchSize){
int i = 0;
List<List<T>> batches = new ArrayList<List<T>>();
while(i<collection.size()){
int nextInc = Math.min(collection.size()-i,batchSize);
List<T> batch = collection.subList(i,i+nextInc);
batches.add(batch);
i = i + nextInc;
}
return batches;
}
请让我知道是否有任何现有的公用事业已经相同。
当前回答
使用Apache Commons ListUtils.partition。
org.apache.commons.collections4.ListUtils.partition(final List<T> list, final int size)
其他回答
Java 8中的一行代码是:
import static java.util.function.Function.identity;
import static java.util.stream.Collectors.*;
private static <T> Collection<List<T>> partition(List<T> xs, int size) {
return IntStream.range(0, xs.size())
.boxed()
.collect(collectingAndThen(toMap(identity(), xs::get), Map::entrySet))
.stream()
.collect(groupingBy(x -> x.getKey() / size, mapping(Map.Entry::getValue, toList())))
.values();
}
下面是一个简单的Java 8+解决方案:
public static <T> Collection<List<T>> prepareChunks(List<T> inputList, int chunkSize) {
AtomicInteger counter = new AtomicInteger();
return inputList.stream().collect(Collectors.groupingBy(it -> counter.getAndIncrement() / chunkSize)).values();
}
这里有一个例子:
final AtomicInteger counter = new AtomicInteger();
final int partitionSize=3;
final List<Object> list=new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
list.add("D");
list.add("E");
final Collection<List<Object>> subLists=list.stream().collect(Collectors.groupingBy
(it->counter.getAndIncrement() / partitionSize))
.values();
System.out.println(subLists);
输入: [a, b, c, d, e]
输出: [a, b, c]， [d, e]]
你可以在这里找到例子: https://e.printstacktrace.blog/divide-a-list-to-lists-of-n-size-in-Java-8/
解决这个问题的另一个方法是:
public class CollectionUtils {
/**
* Splits the collection into lists with given batch size
* @param collection to split in to batches
* @param batchsize size of the batch
* @param <T> it maintains the input type to output type
* @return nested list
*/
public static <T> List<List<T>> makeBatch(Collection<T> collection, int batchsize) {
List<List<T>> totalArrayList = new ArrayList<>();
List<T> tempItems = new ArrayList<>();
Iterator<T> iterator = collection.iterator();
for (int i = 0; i < collection.size(); i++) {
tempItems.add(iterator.next());
if ((i+1) % batchsize == 0) {
totalArrayList.add(tempItems);
tempItems = new ArrayList<>();
}
}
if (tempItems.size() > 0) {
totalArrayList.add(tempItems);
}
return totalArrayList;
}
}
下面的例子演示了一个List的分块:
package de.thomasdarimont.labs;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class SplitIntoChunks {
public static void main(String[] args) {
List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
List<List<Integer>> chunks = chunk(ints, 4);
System.out.printf("Ints: %s%n", ints);
System.out.printf("Chunks: %s%n", chunks);
}
public static <T> List<List<T>> chunk(List<T> input, int chunkSize) {
int inputSize = input.size();
int chunkCount = (int) Math.ceil(inputSize / (double) chunkSize);
Map<Integer, List<T>> map = new HashMap<>(chunkCount);
List<List<T>> chunks = new ArrayList<>(chunkCount);
for (int i = 0; i < inputSize; i++) {
map.computeIfAbsent(i / chunkSize, (ignore) -> {
List<T> chunk = new ArrayList<>();
chunks.add(chunk);
return chunk;
}).add(input.get(i));
}
return chunks;
}
}
输出:
Ints: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
Chunks: [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11]]
