Throw an exception if a Stream has no result

user6601906 :

I need to throw an exception inside lambda and I'm not sure how to do it.

Here is my code so far:

listOfProducts
.stream()
.filter(product -> product.getProductId().equalsIgnoreCase(productId))
.filter(product -> product == null) //like if(product==null) throw exception
.findFirst()
.get()

I have no idea how to do that. Is there any way to do this or I just bypass it by applying filter so that filter will not forward null value like filter(product->product!=null) (even a hint will be useful :))

Edit The actuall question is I need a product and if it is null then it will throw exception otherwise it will pass, it's not mentioned in Java 8 Lambda function that throws exception?

The code I am trying to refactor is

for(Product product : listOfProducts) {
  if(product!=null && product.getProductId()!=null &&
      product.getProductId().equals(productId)){
    productById = product;
    break;
  }
}
if(productById == null){
  throw new IllegalArgumentException("No products found with the
    product id: "+ productId);
}

I have another possible solution as

public Product getProductById(String productId) {
        Product productById = listOfProducts.stream()
                .filter(product -> product.getProductId().equalsIgnoreCase(productId)).findFirst().get();

        if (productById == null)
            throw new IllegalArgumentException("product with id " + productId + " not found!");

        return productById;
    }

But I want to solve it using functional interface and it will be good if I can achieve this using one line in this method like

...getProductById()
return stream...get();

and If I need to declare a custom method to declare exception, it won't be an issue

Didier L :

findFirst() returns an Optional so if you want to have your code throw an exception in case you didn't find anything, you should use orElseThrow to throw it.

listOfProducts
.stream()
.filter(product -> product.getProductId().equalsIgnoreCase(productId))
.findFirst()
.orElseThrow(() -> new IllegalArgumentException("No products found with the  product id: "+ productId));