Java8 - Collections.toMap()方法

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本文详细介绍了如何在Java中使用Collections的toMap()方法，通过People类实例展示如何根据name属性生成key，address属性生成value，以及分别收集单独属性和对象本身的映射过程。

Collections.toMap()方法使用
1）实体类：

@ToString
@Data
@AllArgsConstructor
public class People {

    private Integer id;
    private String name;
    private String address;
    private Integer age;
}

2）测试类

 public static void main(String[] args) {
        People people1 = new People(1, "only-qi1", "bbb", 11);
        People people2 = new People(2, "only-qi2", "ccc", 12);
        People people3 = new People(3, "only-qi3", "dddd", 13);
        People people4 = new People(1, "only-qi4", "fff", 14);
        People people5 = new People(2, "only-qi5", "eee", 15);
        People people6 = new People(1, "only-qi6", "ttttt", 11);
        ArrayList<People> arrayList = new ArrayList<>();
        arrayList.add(people1);
        arrayList.add(people2);
        arrayList.add(people3);
        arrayList.add(people4);
        arrayList.add(people5);
        arrayList.add(people6);

        System.out.println("-----------------toMap()方法: 收集一下集合中每个对象的两个单独的属性---------------");
        Map<String, String> collect = arrayList.stream().collect(Collectors.toMap(People::getName, People::getAddress));
        for (String s : collect.keySet()) {
            System.out.println("key值是：" + s + "=========" + "value的值是" + collect.get(s));
        }

        arrayList.stream().collect(Collectors.toMap(People::getName, p -> p));

        System.out.println("-------------------toMap()方法:收集一下属性和对象本身----------------------");
        Map<String, People> collect1 = arrayList.stream().collect(Collectors.toMap(People::getName, p -> p));
        for (String s : collect1.keySet()) {
            System.out.println("key值是：" + s + "=========" + "value的值是" + collect1.get(s));
        }
    }