Stream API Extension

This Library enables you handling Checked Exception in the Java Stream API. See mapE() in below example.

@ExtensionMethod({StreamExtOps.class})
class RestService {
    List<HttpResponse> sendRequests(List<HttpRequest> requests) {
        return requests.stream()
                .map(req -> executor.submit(() -> httpClient.send(req, ofString())))
                .mapE(Future::get)
                .collect(toList());
    }
}

Future::get throws the checked exception, ExecutionException and InterruptedException. You can't pass Future::get directly in Stream.map(). Instead, you can use mapE() of the Java Standard Stream API extended by this library. When the future.get() throws a checked exception, this library re-throw it with wrapped by FunctionExecutionException.

Extension APIs

mapE(func)

when func throws an exception, re-throw it with wrapped by FunctionExecutionException.

stream()
  .mapE(Future::get)
  .collect(toList());

mapE(func, fallback)

when func throws an exception, fallback function will be called to handle the exception.
fallback should have two params: the first is the source element of the stream, the second is the exception thrown by the func.

stream()
  .mapE(Future::get, (future, exception) -> exception.getMessage())
  .collect(toList());

mapQuiet(func)

when func throws an exception, it maps to null;

stream()
  .mapQuiet(Future::get)   // if fails, map to null
  .collect(toList());

Other extension APIs

flatMapE(func) / flatMapE(func, fallback) / flatMapQuiet(func)
filterE(predicate) / filterE(predicate, fallback) / filterQuiet(predicate)
forEachE(consumer) / forEachE(predicate, fallback) / forEachQuiet(predicate)
anyMatchE / ...
allMatchE / ...
nonMatchE / ...
forEachOrderedE / ...

How works "Quietly" ?

When an exception occurred, Quiet API handles it like the followings.

function in mapQuiet(): returns null
function in flatMapQuiet(): returns an empty Stream
predicate for filterQuiet(), anyMatchQuiet() etc: returns false
consumer for forEachQuiet(), forEachOrderedQuiet(): do nothing

How it extends ?

This library uses lombok's @ExtensionMethod.

@ExtensionMethod({StreamExtOps.class})

By this annotation, the Java Standard Stream API will have the extension methods.

Don't want to use Lombok ?

or already using lombok, but don't want to use experimental features ?

This library also provides some utilities can be used without the lombok. See rethrow() in below example.

    requests.stream()
        .map(req -> executor.submit(() -> httpClient.send(req, ofString())))
        .map(rethrow(Future::get))
        .collect(toList());

Utility APIs

rethrow(func)

when func throws an exception, re-throw it with wrapped by FunctionExecutionException.

stream()
  .map(rethrow(Future::get))
  .collect(toList());

fallback(func, fallbackFunction)

when func throws an exception, fallbackFunction function will be called to handle the exception.
fallbackFunction should have two params: the first is the source element of the stream, the second is the exception thrown by the func.

stream()
  .map(fallback(Future::get, (future, exception) -> exception.getMessage()))
  .collect(toList());

quiet(func)