先取出属性集合，再利用Set去重
 
List<String> productKeys = dtoList.stream().map(HealthSceneDeviceDto::getProductKey).collect(
        Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(k -> k))), ArrayList::new)
);

转载链接：https://blog.csdn.net/Mint6/article/details/78798191/
 
特别注意点：从list集合中取出某个属性时，先要判断是否为null，如果为null会报空指针异常。

package com.hb.test;
 
import java.lang.reflect.Field; 
 import java.util.ArrayList; 
 import java.util.List;
 
public class Test {
 
public static void main(String[] args) throws IllegalArgumentException,
        Exception {
    Person p1 = new Person("111", "aaa");
    Person p2 = new Person("222", "bbb");
    List list = new ArrayList();
    list.add(p1);
    list.add(p2);
    test(list);

}

public static void test(List list) throws Exception, IllegalAccessException {
    for (int i = 0; i < list.size(); i++) {
        Field[] fields = list.get(i).getClass().getDeclaredFields();
        Object oi = list.get(i);
        for (int j = 0; j < fields.length; j++) {
            if(!fields[j].isAccessible()){
                fields[j].setAccessible(true);
            }

            System.out.println(fields[j].get(oi));
        }
    }
}
 
}
 
转载自：http://www.cnblogs.com/hanbin/archive/2011/04/07/2007625.html

 
 
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class test {

    public static void main(String[] args) {

        List<Student> students=new ArrayList<Student>();
        Student student=new Student("小王",18);
        Student student1=new Student("小张",19);
        students.add(student);
        students.add(student1);
        List<Integer> productId=students.stream().map(Student::getAge).collect(Collectors.toList());
        System.out.printf(productId.toString());
    }
}