java8 Stream 大數(shù)據(jù)量List分批處理
//按每3個一組分割
private static final Integer MAX_SEND = 3;
public static void main(String[] args) {
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7);
int limit = countStep(list.size());
//方法一：使用流遍歷操作
List<List<Integer>> mglist = new ArrayList<>();
Stream.iterate(0, n -> n + 1).limit(limit).forEach(i -> {
mglist.add(list.stream().skip(i * MAX_SEND).limit(MAX_SEND).collect(Collectors.toList()));
});
System.out.println(mglist);
//方法二：獲取分割后的集合
List<List<Integer>> splitList = Stream.iterate(0, n -> n + 1).limit(limit).parallel().map(a -> list.stream().skip(a * MAX_SEND).limit(MAX_SEND).parallel().collect(Collectors.toList())).collect(Collectors.toList());
System.out.println(splitList);
}
/**
* 計算切分次數(shù)
*/
private static Integer countStep(Integer size) {
return (size + MAX_SEND - 1) / MAX_SEND;
}
使用google guava對List進行分割
//使用guava對list進行分割
List<User> users = userService.findAll();
//按每50個一組分割
List<List<User>> parts = Lists.partition(users, 50);
parts.stream().forEach(list -> {
process(list);
});
使用apache common collection
List<Integer> intList = Lists.newArrayList(1, 2, 3, 4, 5, 6, 7, 8);
List<List<Integer>> subs = ListUtils.partition(intList, 3);
java 手寫將一個List等分成n個list
public static <T> List<List<T>> averageAssign(List<T> source, int n) {
List<List<T>> result = new ArrayList<>();
int remainder = source.size() % n; //(先計算出余數(shù))
int number = source.size() / n; //然后是商
int offset = 0;//偏移量
for (int i = 0; i < n; i++) {
List<T> value;
if (remainder > 0) {
value = source.subList(i * number + offset, (i + 1) * number + offset + 1);
remainder--;
offset++;
} else {
value = source.subList(i * number + offset, (i + 1) * number + offset);
}
result.add(value);
}
return result;
}
