jpa 分页工具类，把 list 转 page 的工具类

JpaPageUtils.java 工具类

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;

public class JpaPageUtils {
	
	private static Integer defaultPageSize = 10;

	public static <T> Page<T> listToPage(List<T> list, int pageNo) {
		PageRequest pageable = PageRequest.of(pageNo - 1, defaultPageSize);
		return getPage(list, pageable);
	}
	
	public static <T> Page<T> listToPage(List<T> list, int pageNo, int pageSize) {
		PageRequest pageable = PageRequest.of(pageNo - 1, pageSize);
		return getPage(list, pageable);
	}
	
	public static <T> Page<T> getPage(List<T> list) {
		PageRequest pageable = PageRequest.of(0, defaultPageSize);
		return getPage(list, pageable);
	}

	public static <T> Page<T> getPage(List<T> list, Pageable pageable) {
		// 第n页起始值
		int pageStart = pageable.getPageNumber() * pageable.getPageSize();
		// 第n页期望结尾值
		int expectPageEnd = pageStart + pageable.getPageSize() - 1;
		return Optional.of(list.size()).filter(size -> size >= pageStart)
				.map(size -> getRealSubList(pageStart, expectPageEnd, list, pageable))
				.orElseGet(() -> getEmptySubList(list, pageable));
	}

	private static <T> PageImpl<T> getRealSubList(int pageStart, int expectPageEnd, List<T> list, Pageable pageable) {
		int realPageEnd = (list.size() > expectPageEnd) ? expectPageEnd + 1	: list.size();
		return new PageImpl<>(list.subList(pageStart, realPageEnd), pageable, list.size());
	}

	private static <T> PageImpl<T> getEmptySubList(List<T> list, Pageable pageable) {
		return new PageImpl<>(new ArrayList(), pageable, list.size());
	}

}