java8 stream的常用法记录

记录一下工作中常用的java8 stream用法。

package com.example.demo.test;

import com.alibaba.fastjson.JSONArray;
import com.example.demo.beans.entity.TMybatis;
import net.minidev.json.JSONUtil;

import java.util.*;
import java.util.stream.Collectors;

public class StreamTest {
    public static void main(String[] args) throws Exception{
        List<TMybatis> mybatis = new ArrayList<>();
        for(int i=0;i<10;i++){
            TMybatis tMybatis = new TMybatis();
            tMybatis.setObjid(i+1);

            if(i%2 == 0){
                tMybatis.setRemoveTag(1);
            }
            else {
                tMybatis.setRemoveTag(0);
            }

            mybatis.add(tMybatis);
        }

        //求和
        int add = mybatis.stream().collect(Collectors.summingInt(TMybatis::getObjid));
        int add1 = mybatis.stream().collect(Collectors.summingInt(t -> {
            return t.getObjid() + 1;
        }));
        System.out.println(add+","+add1);

        //分组
        Map<Integer,List<TMybatis>> groupBy = mybatis.stream().collect(Collectors.groupingBy(TMybatis::getRemoveTag));

        //List转Map,toMap 如果集合对象有重复的key，会报错Duplicate key ....可以用 (k1,k2)->k1 来设置，如果有重复的key,则保留key1,舍弃key2
        Map<Integer,TMybatis> listToMap = mybatis.stream().collect(Collectors.toMap(TMybatis::getObjid,m->m,(k1,k2)->k1));
        Map<Integer,Integer> listToMap1 = mybatis.stream().collect(Collectors.toMap(TMybatis::getObjid,TMybatis::getRemoveTag));

        //过滤
        List<TMybatis> mybatisNew = mybatis.stream().filter(item -> item.getRemoveTag()==1).collect(Collectors.toList());
        List<TMybatis> mybatisNew1 = mybatis.stream().filter(item -> {
            return item.getRemoveTag() == 0;
        }).collect(Collectors.toList());

        //提取某个字段
        List<Integer> objids = mybatis.stream().map(TMybatis::getObjid).collect(Collectors.toList());
        List<Integer> objids1 = mybatis.stream().map(item -> item.getObjid()+item.getRemoveTag()).collect(Collectors.toList());
        System.out.println(objids);


        //排序
        List<TMybatis> mybatisNew2 = mybatis.stream().sorted(Comparator.comparing(TMybatis::getObjid).reversed().
                thenComparing(TMybatis::getRemoveTag)).collect(Collectors.toList());
        List<TMybatis> mybatisNew3 = mybatis.stream().sorted((o1,o2) -> {
            return o1.getObjid().compareTo(o2.getObjid());
        }).collect(Collectors.toList());

        JSONArray array = new JSONArray(Collections.singletonList(mybatisNew2));
        System.out.println(array.toJSONString());

        //分页
        List<TMybatis> mybatisNew4 = mybatis.stream().skip(2).limit(3).collect(Collectors.toList());
        array = new JSONArray(Collections.singletonList(mybatisNew4));
        System.out.println(array.toJSONString());

        //拼接
        String join = mybatis.stream().map(t -> {
            return t.getObjid().toString();
        }).collect(Collectors.joining(","));
        System.out.println(join);

        //任一匹配
        boolean anyMatch = mybatis.stream().anyMatch(t -> t.getObjid() == 1);
        System.out.println(anyMatch);

    }
}