Optional 类如何优雅进行判空

1-判断对象为空

平常我们写空判断对象代码如下：

Student student = new Student("haha");
        student = null;

        if (student != null) {
            String name = student.getName();
        }

替换为 Optional  类型直进行判空，缺点直接判断 代码依旧冗余。代码如下：

  Optional studentB = Optional.ofNullable(student);
        if (studentB.isPresent()) {
            System.out.println(studentB.get().getName());
        }

正确的做法 建议使用流式操作，代码如下：

  Optional.ofNullable(student).ifPresent(stu -> System.out.println(stu.getName()));

 2-再比如获取获取对象中的类，为空就抛出异常

正常判断为空的写法

   if (student != null) {
            if (student.getAddress() != null) {
                Address address = student.getAddress();
                if (address.getCity() != null) {
                    System.out.println(address.getCity());
                }
            }
        }
        throw new RuntimeException("有空值");

正确的流式操作

       Optional.ofNullable(student)
                .map(Student::getAddress)
                .map(Address::getCity)
                .orElseThrow(() -> new Exception("有空值"));

3-再比如获取名字为小马哥的学生，如果为空就返回一个新对象

平常的写法

 public Student getStudent(Student student) throws RuntimeException {
        if (student != null) {
            String name = student.getName();
            if ("xiaomage".equals(name)) {
                return student;
            }
            student = new Student();
            student.setName("xiaomage");
            return student;
        } else {
            student = new Student();
            student.setName("xiaomage");
            return student;
        }
    }

Optional  流方式操作写法

    public Student getStudent2(Student student) {
        return Optional.ofNullable(student)
                .filter(stu -> "xiaomage".equals(stu.getName()))
                .orElseGet(() -> {
                    Student studentNew = new Student();
                    studentNew.setName("xiaomage");
                    return studentNew;
                });
    }