list stream:List转Map

List中部分字段转Map

public static void main(String[] args) {
        List<TestUser> userList = new ArrayList();

        TestUser one = new TestUser();
        one.setId(1);
        one.setName("这是老大");
        one.setAge(10D);

        TestUser two = new TestUser();
        two.setId(2);
        two.setName("这是老二");
        two.setAge(8.7);

        TestUser three = new TestUser();
        three.setId(3);
        three.setName("这是老三");
        three.setAge(6.4);



        userList.add(one);
        userList.add(two);
        userList.add(three);
        //转换过程中Map对应的key不重复的情况
        Map<Integer, String> userMap = userList.stream().collect(Collectors.toMap(TestUser::getId, TestUser::getName));
        System.out.println(userMap.toString());

        TestUser four = new TestUser();
        four.setId(3);
        four.setAge(6.8);
        four.setName("这是老三的副本");
        userList.add(four);
        //转换过程中Map对应的key存在重复的情况，需要确定相同时选择的value
        Map<Integer, String> userDuplicateMap = userList.stream().collect(Collectors.toMap(TestUser::getId, TestUser::getName, (oldValue, newValue) -> oldValue));
        System.out.println(userDuplicateMap.toString());
    }

List中对象和字段转Map

public static void main(String[] args) {
        List<TestUser> userList = new ArrayList();

        TestUser one = new TestUser();
        one.setId(1);
        one.setName("这是老大");
        one.setAge(10D);

        TestUser two = new TestUser();
        two.setId(2);
        two.setName("这是老二");
        two.setAge(8.7);

        TestUser three = new TestUser();
        three.setId(3);
        three.setName("这是老三");
        three.setAge(6.4);



        userList.add(one);
        userList.add(two);
        userList.add(three);
        //转换过程中Map对应的key不重复的情况
        Map<Integer, TestUser> userMap = userList.stream().collect(Collectors.toMap(TestUser::getId, TestUser -> TestUser));
        System.out.println(userMap.toString());

        TestUser four = new TestUser();
        four.setId(3);
        four.setAge(6.8);
        four.setName("这是老三的副本");
        userList.add(four);
        //转换过程中Map对应的key存在重复的情况，需要确定相同时选择的value
        Map<Integer, TestUser> userDuplicateMap = userList.stream().collect(Collectors.toMap(TestUser::getId,  TestUser -> TestUser, (oldValue, newValue) -> oldValue));
        System.out.println(userDuplicateMap.toString());
    }