ios 字符串转数组java8-list转map判空，分组
/**
* list转map/分组
* @Author: Mr.li
* @Date: 2020/9/8
*/
@Test
public void demo7() {
List<User> userList = new ArrayList<User>() {
{
add(new User("付1", "男1", 20));
add(new User("付1", "男", 20));
add(new User("付2", "男", 21));
add(new User("付3", "男", 22));
add(new User("付4", "男", 23));
add(new User("付5", "男", 24));
add(new User(null, "男", 25));
}
};
User user6 = new User("zhangsan", "男", 24);
userList.add(user6);
/** list 转map
* 注意：要是key重复的话会报错Duplicate key ....
* key name  都是1
* 可以⽤ (k1,k2)->k1 来设置，如果有重复的key，则保留key1，舍弃key2
*/
Map<String, Object> compMap = userList.stream().filter(e-&Name()!=null).Map(User::getName, a -> a.getAge() + "-->" + a.getName(), (k1, k2) -> k1));
/*for (Object obj : compMap.keySet()) {
String key = (String) obj;//取到每⼀个key值
String value = (String) (key);
System.out.println(key + ":" + value);
}*/
compMap.forEach((k,v)->{
System.out.println(k+":"+v);
});
/**
* list中以某个属性分组，⽐如⽤name分组
*/
Map<String, List<User>> map = userList.stream().filter(e-&Name()!=null).upingBy(User::getName));
System.out.println("Map: "+map);
System.out.println("User: "+ getUser(user6));
}
/**
* 得到user
* @Author: Mr.li
* @Date: 2020/9/8
*/
public User getUser(User user) {
return Optional.ofNullable(user)
.filter(u -> "zhangsan".Name()))
.orElseGet(() -> {
User user1 = new User();
user1.setName("zhangsan");
return user1;
});
}
result：

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