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