详细分析请参考:
1.https://www.cnblogs.com/rjzheng/p/9163246.html
2.https://blog.csdn.net/qq_35387940/article/details/105386359

准备实体类

public class Type {

    private BigDecimal id;
    private String name;
	
    // 省略get和set......
}

public class User {

    private BigDecimal id;
    private String avatar;
    private String email;
    // 💤实体类组合
    private Type type;

    // 省略get和set......
}

实例1

⏹获取对象中的属性,若不存在返回默认值

User user = null;

// 😒之前写法,三元表达式
String emailTest1 = ObjectUtils.isEmpty(user) ? "123@qq.com" : user.getEmail();
System.out.println(emailTest1);

// 💪现在写法,可读性更高
String email1 = Optional.ofNullable(user).map(User::getEmail).orElse("123@qq.com");
System.out.println(email1);

实例2

⏹获取嵌套实体类对象中的属性,若不存在则返回默认值

User user = null;

// 😒之前写法,需要不断的判断对象和属性是否为null
BigDecimal typeTestId = null;
if (!ObjectUtils.isEmpty(user)) {
    Type type = user.getType();
    if (!ObjectUtils.isEmpty(type)) {
        typeTestId = type.getId();
    } else {
        typeTestId = BigDecimal.ZERO;
    }
} else {
    typeTestId = BigDecimal.ZERO;
}
System.out.println(typeTestId);

// 💪现在写法,链式调用,只需在最后指定默认值
BigDecimal typeId = Optional.ofNullable(user)
        .map(User::getType)
        .map(Type::getId)
        .orElse(BigDecimal.ZERO);
System.out.println(typeId);

实例3

⏹根据条件获取对象,若满足条件的对象不存在则返回默认对象

User user = null;

// 😒之前写法
User userTest2 = null;
if (!ObjectUtils.isEmpty(user)) {
    String email = user.getEmail();
    if ("110@qq.com".equals(email)) {
        userTest2 = user;
    }
} else {
    userTest2 = new User();
    userTest2.setEmail("110@qq.com");
}
System.out.println(userTest2);

// 💪现在写法
User user2 = Optional.ofNullable(user)
        .filter(item -> "110@qq.com".equals(item.getEmail()))
        .orElseGet(() -> {
            User user1 = new User();
            user1.setEmail("110@qq.com");
            return user1;
        });
System.out.println(user2);