Merge List of Custom Objects to a Single List Object using Streams Java 8

I have ProductInfo object which looks like this

ProductInfo.java

    public class ProductInfo
    {
    private List<String> servicetagInfo;
    }

I have Order object like this which has list of Products info

OrderDetail.java

    public class OrderDetail
    {
    private String orderNum;
    private List<ProductInfo> productInfo;
    }

And then I have a Response object which basically has List of Order objects

Response.java

    public class Response
    {
    private List<OrderDetail> orderInfo;
    }  

I am getting response as expected.But right now in this format

    orderInfo:
    0: {orderNum: "162293591",...}
     productInfo:
     0: {servicetag_info: ["7LSMW33", "49SMW33"]}
     1: {servicetag_info: ["JF6XN33", "CQ5XN33"]}
     2: {servicetag_info: ["5VRR523", "13LR523"]}

Here I am trying to merge productInfo List to be like this

    productInfo:
    0: {servicetag_info: ["7LSMW33", "49SMW33","JF6XN33", "CQ5XN33","5VRR523", "13LR523"]}

Just add all strings into one main property.

Here is my code

    List<String> serviceTagList = new ArrayList<>();
    for (OrderDetail orderDetail : arInvoiceOrderResponseBody.getOrders()) {  //Here i am getting orders from external service
		if (orderDetail != null) {
			if (orderDetail.getProductInfo() != null && orderDetail.getProductInfo().size() > 0) {
				for (ProductInfo productInfoDetail : orderDetail.getProductInfo()) {
					if (productInfoDetail != null) {
						if (productInfoDetail.getServicetagInfo() != null) {
							for (String serviceTag : productInfoDetail.getServicetagInfo()) {
								serviceTagList.add(serviceTag);
							}
                       }
					}
                }
			}
		}
		ProductInfo productInfo = new ProductInfo();
		productInfo.setServicetagInfo(serviceTagList);
		orderDetail.setProductInfo(Arrays.asList(productInfo));
	}         

Can anyone suggest how can i achieve same using streams in java so that it will be readable.

Try this:

Set<String> tags = order.stream()
			.flatMap(order -> order.getProductInfo().stream())
			.map(ProductInfo::getServicetagInfo)
			.collect(Collectors.toSet());

Full implementation:

for (OrderDetail orderDetail : arInvoiceOrderResponseBody.getOrders()) {
    if (orderDetail != null && orderDetail.getProductInfo() != null) {
        orderDetail.getProductInfo().removeAll(null); // Remove any null elems
        Set<String> tags = orderDetail.getProductInfo().stream()
			.flatMap(product -> (product.getServicetagInfo() == null) ? null : product.getServicetagInfo().stream())
			.collect(Collectors.toSet());
        tags.remove(null); // Remove null if exists
    }

    ProductInfo productInfo = new ProductInfo();
    productInfo.setServicetagInfo(tags);
    orderDetail.setProductInfo(Arrays.asList(productInfo));
}

With streams your code could be like this:

arInvoiceOrderResponseBody.getOrders().stream()
            .filter(Objects::nonNull)
            .forEach(YourClassName::mergeProductInfo);

The method mergeProductInfo would be:

private static void mergeProductInfo(OrderDetail orderDetail) {

    List<String> serviceTagList = new ArrayList<>();

    if (orderDetail.getProductInfo() != null) {
        serviceTagList = orderDetail.getProductInfo().stream()
                .filter(Objects::nonNull)
                .map(ProductInfo::getServicetagInfo)
                .filter(Objects::nonNull)
                .flatMap(Collection::stream)
                .collect(Collectors.toList());
    }

    ProductInfo productInfo = new ProductInfo();
    productInfo.setServicetagInfo(serviceTagList);
    orderDetail.setProductInfo(Arrays.asList(productInfo));
}

It could be simplified if you could be sure that you are not going to receive null lists or elements.