求求你,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());
}
}