Throw an exception if a Stream has no result

Question

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

Well, do you need the actual exception, meaning you want to be alerted when there is a product with a null `product`, or do you want to ignore products with that value? — RealSkeptic, Sep 05 '16 at 11:16
Possible duplicate of [Java 8 Lambda function that throws exception?](http://stackoverflow.com/questions/18198176/java-8-lambda-function-that-throws-exception) — ACV, Sep 05 '16 at 11:17
actually `filter(product->product!=null)` will not allow null value to pass, and therefore can result in crash, and therefore yes I want to be notified — , Sep 05 '16 at 11:20
If possible you should use `ifPresent` rather than `get` on the `Optional` or you could use `orElseThrow` — greg-449, Sep 05 '16 at 11:36

score 35 · Accepted Answer · answered Sep 05 '16 at 11:39

35

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));

answered Sep 05 '16 at 11:39

Didier L

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@HelloWorld: Just a side note, your original code skips `null` elements and will only fail, if there is no matching (non-`null`) element, whereas this code will immediately fail if it encounters a `null` value before the match. You have to make up your mind whether `null`s ought to be allowed in the `listOfProducts` or not. – Holger Sep 05 '16 at 11:53
1

@Holger Indeed, I removed the null check filter as the comment indicated that it was intended to throw an exception. However the non-stream code also had this null check, but then the stream version should have it before the product id filter, otherwise the latter will throw an NPE. – Didier L Sep 05 '16 at 11:56
I added this in final return `listOfProducts.stream() .filter(product -> product.getProductId().equalsIgnoreCase(productId)) .filter(product -> product != null).findFirst() .orElseThrow(() -> new IllegalArgumentException("product not found " + productId));` hope it will block null value – Sep 05 '16 at 11:57
@Holger, it will check for null and I don't think I need to throw exception here :) – Sep 05 '16 at 11:58
1

@HelloWorld: you have to apply the `null` filter *before* the other as otherwise, the attempt to invoke `product.getProductId()` will already cause a `NullPointerException` if the stream encounters `null`. – Holger Sep 05 '16 at 12:56
Didier L my question : if listOfProducts is empty then i want to throw an exception, saying that list of products is empty how can we do that. – Vijender Kumar Dec 11 '17 at 12:54
@VijenderKumar well just test if the list is empty and then throw your exception… If your need is more complex like that I suggest search for other similar question and then ask your own if necessary with the details of what you have tried. – Didier L Dec 11 '17 at 12:59

score 0 · Answer 2 · answered Aug 19 '21 at 10:40

Below code would work

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

We can write the same with filter chaining as well.

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

Throw an exception if a Stream has no result

2 Answers2