字符串转 —> 数组
核心方法：
String columnIdstr = "2,3,4,5,6,7,8";
Long[] arr = Stream.of(columnIdstr.split(","))
.map(Long::valueOf) //转换
.collect(Collectors.toList()) //流转集合
.toArray(new Long[0]); //集合转Array
List分组后，转换为Map
核心方法：
User user1 = new User(1, "zhangsan", "男", "2018", "2019");
User user2 = new User(2, "王五", "男", "2018", "2019");
User user3 = new User(3, "lisi", "男", "2018", "2019");
User user4 = new User(4, "赵四", "男", "2019", "2019");
User user5 = new User(5, "lisa", "女", "2019", "2019");
User user6 = new User(6, "lucy", "女", "2019", "2019");
List<User> list = new ArrayList();
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
list.add(user5);
list.add(user6);
Map<String, List<User>> detailsMap01 = list.stream()
.collect(Collectors.groupingBy(User::getRegisterTime));
System.out.println(""+detailsMap01.toString());
User实体对象：
public class User {
Integer id;
String openId;
String securityCode;
String registerTime;
String lastActiveTime;
public User() {
}
public User(Integer id, String openId, String securityCode, String registerTime, String lastActiveTime) {
this.id = id;
this.openId = openId;
this.securityCode = securityCode;
this.registerTime = registerTime;
this.lastActiveTime = lastActiveTime;
}
}
// 省去get set方法......
运行结果：
{2019=[User(id=4, openId=赵四, securityCode=男, registerTime=2019, lastActiveTime=2019), User(id=5, openId=lisa, securityCode=女, registerTime=2019, lastActiveTime=2019), User(id=6, openId=lucy, securityCode=女, registerTime=2019, lastActiveTime=2019)], 2018=[User(id=1, openId=zhangsan, securityCode=男, registerTime=2018, lastActiveTime=2019), User(id=2, openId=王五, securityCode=男, registerTime=2018, lastActiveTime=2019), User(id=3, openId=lisi, securityCode=男, registerTime=2018, lastActiveTime=2019)]}
未完待续。。。
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