Optional

记录下test

（Optional.ofNullable）

Optional.ofNullable(user）:user可为空也可非空
Optional.of（user）:user不可为空，空报npe

（Optional.ofNullable.orElse）

@Data
public class UserModel {
    private Integer id;
    private String name;
    private Date date;
    private int age;

    public UserModel(Integer id, String name, Date date, int age) {
        this.id = id;
        this.name = name;
        this.date = date;
        this.age = age;
    }
}

 @Test
    public void givenEmpty() {
        UserModel user = new UserModel(2, "x", new Date(), 23);
        log.debug("Using orElse");
        UserModel result = Optional.ofNullable(user).orElse(createNewUser());
        System.err.println(JSON.toJSONString(result));
        log.debug("Using orElseGet");
        UserModel result2 = Optional.ofNullable(user).orElseGet(() -> createNewUser());
    }

    private UserModel createNewUser() {
        System.err.println("Creating New User");
        return new UserModel(1, "extra", new Date(), 12);
    }

当user为空时
输出为见下面：orElse()和orElseGet一样

16:26:27.705 [main] DEBUG com.example.demo.lambda.StreamTest - Using orElse
Creating New User
{"age":12,"date":1562833587707,"id":1,"name":"extra"}
16:26:27.796 [main] DEBUG com.example.demo.lambda.StreamTest - Using orElseGet
Creating New User

但是当user不为空时
输出为见下面：可以看到orElse（）后面的语句依然会执行，但是orElseGet(）不会执行，所以日常推荐使用orElseGet(),提升性能

16:23:35.197 [main] DEBUG com.example.demo.lambda.StreamTest - Using orElse
Creating New User
{"age":23,"date":1562833415196,"id":2,"name":"x"}
16:23:35.318 [main] DEBUG com.example.demo.lambda.StreamTest - Using orElseGet

Optional.ofNullable.map