Java Optional usage

OptionalFilter.java

// Before
public Member getMemberIfExceedsBasePrice(Order order, long basePrice) {
	if (order != null && order.getTotalPrice() > basePrice) {
		return order.getMember();
	}
}

// After
public Optional<Member> getMemberIfExceedsBasePrice(Order order, long basePrice) {
	return Optional.ofNullable(order)
			.filter(order -> order.getTotalPrice() > basePrice)
			.map(Order::getMember);
}

OptionalIfPresent.java

Optional<Product> optionalProduct = Optional.ofNullable(products.get("nonExists"));
optionalProduct.ifPresent(product -> {
  System.out.println("productName : " + product.getName());
};

OptionalMap.java

// Before
public String getCityOfMemberFromOrder(Order order) {
  if (order!=null) {
    Member member = order.getMember();
    
    if (member!=null) {
      Address address = member.getAddress();
      
      if (order.getMember().getAddress()!=null) {
        return address.getCity();
      }
    }
  }
  
  return "Seoul";
}

// After
public String getCityOfMemberFromOrder(Order order) {
	return Optional.ofNullable(order)
			.map(Order::getMember)
			.map(Member::getAddress)
			.map(Address::getCity)
			.orElse("Seoul");
}

OptionalNullsafeValue.java

// Before
public long getSpecificProductPrice(Map<Product> products) {
  Product product = products.get("nonExists");
  
  if (products!=null) {
    return product.getPrice();
  } else {
    return 0L;
  }
}

// After
public long getSpecificProductPrice(Map<Product> products) {
  Optional<Product> optionalProduct = Optional.ofNullable(products.get("nonExists"));
  
  return optionalProduct.map(Product::getPrice).orElse(0L);
}