如何优雅的判断List集合中对象的某个字段是否存在重复值

Posted 2021-09-20 Firm陈

今天碰到一个需要判断泛型集合中的对象的某个字段是否有重复值的需求，特在此对方法进行记录。
这里我们使用了Java8的新特性Strem流，详细代码如下。
实体类如下：

/**  
 * @Title: Person.java
 * @Description: TODO(描述)
 * @author Soul
 */
public class Person {

	private String name;
	private Integer age;
	private String gradle;
	
	public Person() {
		super();
	}
	
	public Person(String name, Integer age, String gradle) {
		super();
		this.name = name;
		this.age = age;
		this.gradle = gradle;
	}
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	public String getGradle() {
		return gradle;
	}
	public void setGradle(String gradle) {
		this.gradle = gradle;
	}
	
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", gradle=" + gradle + "]";
	} 
	
}

测试代码如下：

public static void main(String[] args) {
		 Person person1 = new Person("小刘", 24, "男");
        Person person2 = new Person("小贺", 18, "女");
        Person person3 = new Person("小袁", 18, "女");
        Person person4 = new Person("小李", 21, "男");
        Person person5 = new Person("小子", 21, "男");
        List<Person> persons = Arrays.asList(person1, person2, person3, person4,person5);

        // 根据指定属性分组，并统计数量（key：指定属性，value：数量）
        Map<Object, Long> mapGroup = persons.stream().collect(Collectors.groupingBy(person -> person.getAge(), Collectors.counting()));
        System.out.println(mapGroup.toString());

        // 筛选Map中value大于1的key
        Stream<Object> stringStream = mapGroup.entrySet().stream().filter(entry -> entry.getValue() > 1).map(entry -> entry.getKey());
        System.out.print("重复的数据：{ ");
        stringStream.forEach(str -> {
            System.out.print(str + " ");
        });
        System.out.println("}");
	}

运行结果如图所示：