Java不要再使用!=null判空了！

/**
* @author Axin
* @since 2020-09-20
* @summary 一个User类定义
 * （Ps：Data 是lombok组件提供的注解，简化了get set等等的约定代码）
*/

@Data
public class User {
 private String name;
 private String gender;
 private School school;
 @Data
 public static class School {
 private String scName;
 private String adress;
 }
}

public static void main(String[] args) {
 User axin = new User();
 User.School school = new User.School();
 axin.setName("hello");
 if (Objects.nonNull(axin) && Objects.nonNull(axin.getSchool())) {
 User.School userSc = axin.getSchool();
 System.out.println(userSc.getAdress());
 }
}

public static void main(String[] args) {
 User axin = new User();
 User.School school = new User.School();
 axin.setName("hello");
 // 1. 基本调用
 String value1 = OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress).get();
 System.out.println(value1);
}

/**
* @author Axin
* @since 2020-09-10
* @summary 链式调用 bean 中 value 的方法
*/

public final class OptionalBean<T> {
 private static final OptionalBean<?> EMPTY = new OptionalBean<>();
 private final T value;
 private OptionalBean() {
 this.value = null;
 }

 /**
 * 空值会抛出空指针
 * @param value
 */

 private OptionalBean(T value) {
 this.value = Objects.requireNonNull(value);
 }

 /**
 * 包装一个不能为空的 bean
 * @param value
 * @param <T>
 * @return
 */

 public static <T> OptionalBean<T> of(T value) {
 return new OptionalBean<>(value);
 }

 /**
 * 包装一个可能为空的 bean
 * @param value
 * @param <T>
 * @return
 */

 public static <T> OptionalBean<T> ofNullable(T value) {
 return value == null ? empty() : of(value);
 }

 /**
 * 取出具体的值
 * @param fn
 * @param <R>
 * @return
 */

 public T get() {
 return Objects.isNull(value) ? null : value;
 }

 /**
 * 取出一个可能为空的对象
 * @param fn
 * @param <R>
 * @return
 */

 public <R> OptionalBean<R> getBean(Function<? super T, ? extends R> fn) {
 return Objects.isNull(value) ? OptionalBean.empty() : OptionalBean.ofNullable(fn.apply(value));
 }

 /**
 * 如果目标值为空 获取一个默认值
 * @param other
 * @return
 */

 public T orElse(T other) {
 return value != null ? value : other;
 }

 /**
 * 如果目标值为空 通过lambda表达式获取一个值
 * @param other
 * @return
 */

 public T orElseGet(Supplier<? extends T> other) {
 return value != null ? value : other.get();
}

 /**

 * 如果目标值为空 抛出一个异常
 * @param exceptionSupplier
 * @param <X>
 * @return
 * @throws X
 */

 public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
 if (value != null) {
  return value;
 } else {
  throw exceptionSupplier.get();
 }
 }

 public boolean isPresent() {
 return value != null;
 }

 public void ifPresent(Consumer<? super T> consumer) {
 if (value != null)
  consumer.accept(value);
 }

 @Override
 public int hashCode() {
 return Objects.hashCode(value);
 }

 /**
 * 空值常量
 * @param <T>
 * @return
 */

 public static<T> OptionalBean<T> empty() {
 @SuppressWarnings("unchecked")
 OptionalBean<T> none = (OptionalBean<T>) EMPTY;
 return none;
 }
}

public static void main(String[] args) {
 User axin = new User();
 User.School school = new User.School();
 axin.setName("hello");

 // 1. 基本调用
 String value1 = OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress).get();
 System.out.println(value1);
 // 2. 扩展的 isPresent方法 用法与 Optional 一样
 boolean present = OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress).isPresent();
 System.out.println(present);

 // 3. 扩展的 ifPresent 方法
 OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress)
  .ifPresent(adress -> System.out.println(String.format("地址存在:%s", adress)));

 // 4. 扩展的 orElse
 String value2 = OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress).orElse("家里蹲");
 System.out.println(value2);

 // 5. 扩展的 orElseThrow
 try {
 String value3 = OptionalBean.ofNullable(axin)
  .getBean(User::getSchool)
  .getBean(User.School::getAdress).orElseThrow(() -> new RuntimeException("空指针了"));
 } catch (Exception e) {
 System.out.println(e.getMessage());
 }

}