把list放进map中

Question

有个这样的List<PerformanceRanking> list PerformanceRanking是实体类，从数据库查询出来的，相当于一个map

把list放进map中 Map<String,List<PerformanceRanking>> 我想把这个map按照实体类中的三个字段作为String。该如何实现呢

 

Answer 1

    class A {
        private String id;
        private String address;
        private int age;
        private boolean sex;

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        public String getAddress() {
            return address;
        }

        public void setAddress(String address) {
            this.address = address;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }

        public boolean isSex() {
            return sex;
        }

        public void setSex(boolean sex) {
            this.sex = sex;
        }

        public A(String id, String address, int age, boolean sex) {
            this.id = id;
            this.address = address;
            this.age = age;
            this.sex = sex;
        }
    }
    @Test
    public void testA() {
        List<A> aList = new ArrayList<>();
        A a1 = new A("1", "地址1", 10, false);
        aList.add(a1);
        A a2 = new A("1", "地址1", 10, true);
        aList.add(a2);
        A a3 = new A("2", "地址2", 12, false);
        aList.add(a3);
        A a4 = new A("2", "地址2", 12, true);
        aList.add(a4);

        Map<String, List<A>> map = aList.stream().collect(Collectors.groupingBy(a -> a.id+"_"+a.address+"_"+a.age, Collectors.toList()));
        System.out.println(map);
    }