按固定数量拆分列表

Google Guava的Lists.partition方法

源码分析

Lists.java

import com.google.common.collect.Lists;

public class ListSplitter {

    public static <E> List<List<E>> splitList(List<E> sourceList, int size) {
        if (sourceList == null) {
            throw new IllegalArgumentException("源列表不能为空");
        }
        if (size <= 0) {
            throw new IllegalArgumentException("分区大小必须大于0");
        }
        return (sourceList instanceof java.util.RandomAccess) ? 
                new RandomAccessPartition<>(sourceList, size) : new Partition<>(sourceList, size);
    }

    private static class Partition<E> extends AbstractList<List<E>> {
        private final List<E> list;
        private final int partitionSize;

        Partition(List<E> list, int partitionSize) {
            this.list = list;
            this.partitionSize = partitionSize;
        }

        @Override
        public List<E> get(int index) {
            int start = index * partitionSize;
            int end = Math.min(start + partitionSize, list.size());
            return list.subList(start, end);
        }

        @Override
        public int size() {
            return (int) Math.ceil((double) list.size() / partitionSize);
        }
    }

    private static class RandomAccessPartition<E> extends Partition<E> implements java.util.RandomAccess {
        RandomAccessPartition(List<E> list, int partitionSize) {
            super(list, partitionSize);
        }
    }
}

使用示例

List<Long> numbers = java.util.stream.LongStream.rangeClosed(1, 400).boxed().toList();
List<List<Long>> partitions = ListSplitter.splitList(numbers, 100);

注意事项

• 外层列表不可修改，但可以修改内部元素。
• 子列表与原列表共享数据，修改子列表会影响原列表。

Apache Commons Collections的ListUtils.partition方法

源码分析

ListUtils.java

import org.apache.commons.collections4.ListUtils;

public class ApacheListSplitter {

    public static <T> List<List<T>> splitList(List<T> sourceList, int size) {
        if (sourceList == null) {
            throw new IllegalArgumentException("源列表不能为空");
        }
        if (size <= 0) {
            throw new IllegalArgumentException("分区大小必须大于0");
        }
        return new Partition<>(sourceList, size);
    }

    private static class Partition<T> extends AbstractList<List<T>> {
        private final List<T> list;
        private final int partitionSize;

        Partition(List<T> list, int partitionSize) {
            this.list = list;
            this.partitionSize = partitionSize;
        }

        @Override
        public List<T> get(int index) {
            int start = index * partitionSize;
            int end = Math.min(start + partitionSize, list.size());
            return list.subList(start, end);
        }

        @Override
        public int size() {
            return (int) Math.ceil((double) list.size() / partitionSize);
        }
    }
}

使用示例

List<Long> numbers = java.util.stream.LongStream.rangeClosed(1, 400).boxed().toList();
List<List<Long>> partitions = ApacheListSplitter.splitList(numbers, 100);

注意事项

• 类似于Guava实现，外层列表不可修改。

平均分成N份

Java Stream的方法

使用示例

List<Long> numbers = java.util.stream.LongStream.rangeClosed(1, 400).boxed().toList();
int maxSize = 10;
int limit = (numbers.size() + maxSize - 1) / maxSize;
List<List<Long>> partitions = java.util.stream.Stream.iterate(0, n -> n + 1)
    .limit(limit)
    .map(a -> numbers.stream().skip(a * maxSize).limit(maxSize).toList())
    .toList();

注意事项

• 并行流可能影响顺序，需根据实际情况调整。