list.stream笔记-过滤-去重-转map、List等

代码

import vo.PosDataDetailVo;

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

public class AbcMain {
    public static void main(String[] args) throws InterruptedException {
        List<PosDataDetailVo> list = new ArrayList<>();
        PosDataDetailVo posDataDetailVo = new PosDataDetailVo();
        posDataDetailVo.setAccountNo("张三");
        posDataDetailVo.setBankCard("A1");
        list.add(posDataDetailVo);
        PosDataDetailVo posDataDetailVo2 = new PosDataDetailVo();
        posDataDetailVo2.setAccountNo("");
        posDataDetailVo2.setBankCard("B2");
        list.add(posDataDetailVo2);
        PosDataDetailVo posDataDetailVo3 = new PosDataDetailVo();
        posDataDetailVo3.setAccountNo("李四");
        posDataDetailVo3.setBankCard("C3");
        list.add(posDataDetailVo3);
        PosDataDetailVo posDataDetailVo4 = new PosDataDetailVo();
        posDataDetailVo4.setAccountNo("李四");
        posDataDetailVo4.setBankCard("D5");
        list.add(posDataDetailVo4);

        System.out.println("------------");
        System.out.println("按照 AccountNo 去重");
        List<PosDataDetailVo> collect2 = list.stream().collect(Collectors.collectingAndThen(
                Collectors.toCollection(
                        () -> new TreeSet<>(Comparator.comparing(PosDataDetailVo::getAccountNo))
                ), ArrayList::new)
        );
        for (PosDataDetailVo dataDetailVo : collect2) {
            System.out.println(dataDetailVo);
        }
        System.out.println("------------");

        Thread.sleep(2000);
        System.out.println("循环出 AccountNo = 张三 的数据");
        list.stream().filter(posDataDetailVo1 -> "张三".equals(posDataDetailVo1.getAccountNo())).forEach(posDataDetailVo1 -> {
            System.out.println(posDataDetailVo1);
        });
        System.out.println("------------");

        System.out.println("取出 AccountNo = 李四 的数据");
        List<PosDataDetailVo> collect = list.stream().filter(posDataDetailVo1 -> "李四".equals(posDataDetailVo1.getAccountNo())).collect(Collectors.toList());
        for (PosDataDetailVo dataDetailVo : collect) {
            System.out.println(dataDetailVo);
        }
        System.out.println("------------");

        System.out.println("转为map，AccountNo为key，BankCard为value，并且如果key存在重复就取第二个数据");
        Map<String, String> collect1 = list.stream().collect(Collectors.toMap(PosDataDetailVo::getAccountNo, PosDataDetailVo::getBankCard, (v1, v2) -> v2));
        System.out.println(collect1);
        System.out.println("------------");

        System.out.println("将AccountNo = 李四 的数据转为List<String>");
        //如果不需要过滤器，那么就删掉filter过滤器
        List<String> stringList = list.stream().filter(posDataDetailVo1 -> "李四".equals(posDataDetailVo1.getAccountNo())).map(PosDataDetailVo::getAccountNo).collect(Collectors.toList());
        //也可以用下面这种方式，一样的
        //List<String> stringList = list.stream().filter(posDataDetailVo1 -> "李四".equals(posDataDetailVo1.getAccountNo())).map(posDataDetailVo1 -> posDataDetailVo1.getAccountNo()).collect(Collectors.toList());
        for (String s : stringList) {
            System.out.println(s);
        }
        System.out.println("------------");

        System.out.println("List<String>去重");
        List<String> myList= Arrays.asList("a","b","b","c","c","d");
        List<String> myListNew = myList.stream().distinct().collect(Collectors.toList());
        System.out.println(myListNew);
        System.out.println("------------");

        //查找AccountNo=李四，并且BankCard=D5 的元素，存在返回true，不存在返回fasle
        //anyMatch、allMatch、noneMatch自行百度有什么区别
        boolean exist = list.stream().anyMatch(data -> {
            boolean equals1 = "李四".equals(data.getAccountNo());
            boolean equals2 = "D5".equals(data.getBankCard());
            return equals1 && equals2;
        });
        //简写Lambda方式
        //boolean exist = list.stream().anyMatch(data -> "李四".equals(data.getAccountNo()) && "D5".equals(data.getBankCard()));
        System.out.println(exist);

    }
}

运行结果

------------
按照 AccountNo 去重
PosDataDetailVo{accountNo='', bankCard='B2'}
PosDataDetailVo{accountNo='张三', bankCard='A1'}
PosDataDetailVo{accountNo='李四', bankCard='C3'}
------------
循环出 AccountNo = 张三 的数据
PosDataDetailVo{accountNo='张三', bankCard='A1'}
------------
取出 AccountNo = 李四 的数据
PosDataDetailVo{accountNo='李四', bankCard='C3'}
PosDataDetailVo{accountNo='李四', bankCard='D5'}
------------
转为map，AccountNo为key，BankCard为value，并且如果key存在重复就取第二个数据
{=B2, 李四=D5, 张三=A1}
------------
将AccountNo = 李四 的数据转为List<String>
李四
李四
------------
List<String>去重
[a, b, c, d]
------------
true