java 新特性简化代码Optional方法详细讲解【干货】

/** 
 * 对象
 * User(id=null, name=null, age=null, address=null)
 * Address(x=null, y=null, location=null)
*/

/**
 * 如果user不为空则获取Address对象，过滤location属性空值，如果有值则打印user对象
 */
Optional.ofNullable(user)
    .map(User::getAddress)
    .filter(entity->entity.getLocation()!=null)
    .ifPresent(consumer->{
      System.out.println(user);
  });
Address address2= new Address();
address2.setLocation("上海");

/**
 * 如果entity里面的getLocation不为空则取entity对象值，否则取address2对象  不管有没有值orElse都会执行
 */
Address address11 = Optional.ofNullable(user)
          .map(User::getAddress)
          .filter(entity -> entity.getLocation() != null)
          .orElse(address2);

/**
 *  如果entity里面的getLocation不为空则取entity对象值，否则取抛出异常
 */
Address address22 = Optional.ofNullable(user)
          .map(User::getAddress)
          .filter(entity -> entity.getLocation() != null)
          .orElseThrow(()->new RuntimeException("错误"));

/**
 * 如果entity里面的getLocation不为空则取entity对象值，否则取address2对象  与orElse的区别就是orElseGet在没有值的情况下才会执行，有值则不执行orElseGet
 */
Address address33 = Optional.ofNullable(user)
          .map(User::getAddress)
          .filter(entity -> entity.getLocation() != null)
          .orElseGet(()->new Address());