Java List集合假排序分页

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Java List集合假排序分页

我们在进行项目开发的时候可能会遇到一些获取屏幕宽度，dp px的相互转换等问题，我们当然不能每用一次就复制粘贴一次。这时候就需要一个利器-工具类。 这个工具类包含了我们一些公用的方法，只需要一句话我们就可以拿到想要的结果，既精简了我们的代码又省下了我们宝贵的时间。同时，一个好的软件工程师，万能的工具类便是他的护身法宝。（本段引用自：Android 项目开发必备-Utils类的建立与使用）

package com.common;

import java.util.Comparator;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Collectors;


public class SortPageBuilder {

    
    @SuppressWarnings("all")
    private static final Comparator NATURAL_COMPARATOR = Comparator.nullsLast(Comparator.naturalOrder());

    
    @SuppressWarnings("all")
    private static final Comparator REVERSE_COMPARATOR = Comparator.nullsLast(Comparator.reverseOrder());

    
    public  SortPage setRecords(List records){
        return new SortPage<>(records);
    }

    public static class SortPage {

        private List records;

        public SortPage(List records) {
            this.records = records;
        }

        
        @SafeVarargs
        public final > SortPage sortByAsc(Function ...functions){
            if (Objects.isNull(records) || Objects.isNull(functions)) {
                return this;
            }

            Comparator comparator = Comparator.comparing(functions[0], NATURAL_COMPARATOR);

            for (Function function : functions) {
                if (!Objects.equals(function, functions[0])){
                    comparator.thenComparing(function, NATURAL_COMPARATOR);
                }
            }

            records = records.stream().sorted(comparator).collect(Collectors.toList());
            return this;
        }

        
        @SafeVarargs
        public final > SortPage sortByDesc(Function ...functions){
            if (Objects.isNull(records) || Objects.isNull(functions)) {
                return this;
            }

            Comparator comparator = Comparator.comparing(functions[0], REVERSE_COMPARATOR);

            for (Function function : functions) {
                if (!Objects.equals(function, functions[0])){
                    comparator.thenComparing(function, REVERSE_COMPARATOR);
                }
            }

            records = records.stream().sorted(comparator).collect(Collectors.toList());
            return this;
        }

        
        public final SortPage sort(Comparator comparator){
            if (Objects.isNull(records) || Objects.isNull(comparator)) {
                return this;
            }
            records = records.stream().sorted(comparator).collect(Collectors.toList());
            return this;
        }

        
        public SortPage page(Long page, Long limit) {
            if (Objects.isNull(records) || Objects.isNull(page) || Objects.isNull(limit)) {
                return this;
            }
            records = records.parallelStream().skip((page - 1) * limit).limit(limit).collect(Collectors.toList());
            return this;
        }

        
        public List collect() {
            return records;
        }

    }

}