使用java8 Optional防止空指针

 

阿里规范推荐使用

 

 

java8的Optional中，上面两个方法是最长用的

 

1.ofNullable(T) 意思就是可以为空的范型

2.of(T) 值不能为空，否则会抛出NullPointerException

 

 

 

 

 

 

 

 

使用

public class Test {

    public static void main(String[] args) {

        User u1 = null;

        User u2 = new User("111", "yuan");


        System.out.println(print(u1));

        System.out.println(print(u2));


    }

    private static String print(User user) {

        return Optional.ofNullable(user).map(User::toString).orElse("");

    }

}

@Data

@NoArgsConstructor

@AllArgsConstructor

@ToString

public class User {

    private String id;

    private String name;

}

 

输出

 

User(id=111, name=yuan)

 

 

示例2

@Data

@NoArgsConstructor

@AllArgsConstructor

@ToString

public class Employee {

    private String name;

}

@Data

@NoArgsConstructor

@AllArgsConstructor

@ToString

public class Company {

    private String name;

    private List employees;

}

 

public class OptionalTest2 {

    public static void main(String[] args) {

        Employee employee1 = new Employee("zhangsan");

        Employee employee2 = new Employee("lisi");


        Company company = new Company("company1", Arrays.asList(employee1, employee2));


//        company.setEmployees(null);


        // 取出Company中的Employee列表，如果有，那么返回该Employee列表；

        // 如果没有，那么返回一个空的Employee列表。

        Optional optional = Optional.ofNullable(company);

        List result =

                optional.map(Company::getEmployees)

                .orElse(Collections.emptyList());


        result.forEach(employee -> System.out.println(employee.getName()));

    }

}

结果

zhangsan

lisi