实体类

package po;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.io.Serializable;@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student implements Serializable {/*** 姓名*/private String name;/*** 地址*/private Address address;
}

package po;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@AllArgsConstructor
@Data
@NoArgsConstructor
public class Address {/*** 城市*/private String city;
}

以前对空指针的判断

package com.demo;import po.Address;
import po.Student;public class TestCase {public static void main(String[] args) {Student student = new Student("张三",new Address("香港"));student = null;if (null != student){Address address = student.getAddress();if (null != address){if (null != address.getCity()){System.out.println(address.getCity());}}}throw new RuntimeException("学生地址信息不能为空");}
}

Optional处理空指针

package com.demo;import po.Address;
import po.Student;import java.util.Optional;public class TestCase2 {public static void main(String[] args) {Student student = new Student("张三", new Address("香港"));student = null;String address =Optional.ofNullable(student).map(Student::getAddress).map(Address::getCity).orElseThrow(() -> new RuntimeException("学生地址信息不能为空"));System.out.println(address);}
}

测试结果

student为null,抛出空指针异常

不为空指针异常的时候，输出字符串