An overview,

During development, there was a requirement to split a List into sublists of a specified size. The requirement was very simple. Here are two ways to do this:

• Write your own Java code implementation
• Use the utility classes provided by Guava

Two, write Java code implementation

The implementation code is as follows:

    public static <T> List<List<T>> partition(List<T> list, int size) {
        List<List<T>> result = new ArrayList<>();
        if (list == null) {
            throw new NullPointerException("List cannot be null");
        }
        if (size <= 0) {
            throw new IllegalArgumentException("Size must be greater than 0");
        }
        if (list.size() < size) {
            result.add(list);
        } else {
            int r = list.size() / size;
            for (int i = 0; i < r; i++) {
                List<T> subList = list.subList(i * size, (i + 1) * size);
                result.add(subList);
            }
            if(r * size < list.size()) { List<T> subList = list.subList(r * size, list.size()); result.add(subList); }}return result;
    }
Copy the code

Third, use the tool class provided by Guava

Step 1: Add dependencies

<! -- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>30.0 the jre</version>
</dependency>
Copy the code

Step 2: Call Lists. Partition

public static void main(String[] args) {
    List<String> idList = new ArrayList<>();
    for (int i = 0; i < 25; i++) {
        idList.add(UUID.randomUUID().toString());
    }
    List<List<String>> partition = Lists.partition(idList, 3);
    for(List<String> strings : partition) { System.out.println(strings.size()); System.out.println(strings); }}Copy the code