JAVA8 steam 常用示例

package hk.org.ha.tims;

import hk.org.ha.tims.dto.vo.UserRoleVo;
import lombok.Data;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;


public class StreamTest {
    public static void main(String[] args) {
        List<TestVO> demoList = Arrays.asList(new TestVO("1","张三"),new TestVO("2","李四"),new TestVO("3","王五"),new TestVO("4","王五"));
        List<TestVO> demoList1 = Arrays.asList(new TestVO("1","张三"),new TestVO("2","李四"),new TestVO("3","王五"),new TestVO("4","王五"));
        // for 循环
        demoList.stream().forEach(item->{
            System.out.println(item.toString());
        });
        demoList.forEach(item->{
            System.out.println(item.toString());
        });
　　　　// 获取某个字段的list
　　　　List<String> names = demoList.stream().map(TestVO::getName).collect(Collectors.toList());

        //集合转map
        Map<String,String> idNameMap = demoList.stream().collect(Collectors.toMap(TestVO::getId, TestVO::getName));
        Map<String,TestVO> idVOMap = demoList.stream().collect(Collectors.toMap(TestVO::getId, Function.identity()));
            //key重复处理
        Map<String,TestVO> duplicateKeyMap = demoList.stream().collect(Collectors.toMap(TestVO::getId, Function.identity(),(item1,item2)->item2));
　　　　　//分组
　　　　

　　　　Map<String,List<TestVO>> idGroupMap =demoList.stream().collect(Collectors.groupingBy(TestVO::getId,Collectors.toList()));

        //过滤
        List<TestVO> filterResult = demoList.stream().filter(item->"李四".equals(item.getName())).collect(Collectors.toList());

        //根据某个字段去重
        List<TestVO> distinctResult = demoList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(TestVO::getName))), ArrayList::new));


        //limit 取前N条
        demoList.stream().limit(2).collect(Collectors.toList());

        //skip 跳过前N条
        demoList.stream().skip(2).collect(Collectors.toList());

        //排序
        demoList.stream().sorted(new Comparator<TestVO>() {
            @Override
            public int compare(TestVO o1, TestVO o2) {
                return o1.getId().compareTo(o2.getId());
            }
        });


        // 合并
        List<TestVO> resultList = Stream.concat(demoList.stream(),demoList1.stream()).collect(Collectors.toList());

        //parallelStream
        demoList.parallelStream().forEach(item->{
            System.out.println(item.toString());
        });
        


    }
}
@Data
class TestVO{
    private String id;
    private String name;

    public TestVO(String id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "TestVO{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}