collector

May 9, 2021 stream collector api

Teeing, a hidden gem in the Java API

Last week, I described a use-case for a custom Stream Collector. I received a intriguing comment on Twitter: There was a 'Not Found' error fetching URL: 'https://twitter.com/Miguucm/status/1389258245886390292' Hats off to you, Miguel! Your comment revealed a method I didn’t know! So I decided to investigate what the teeing() method is about. Returns a Collector that is a composite of two downstream collectors.

May 2, 2021 stream collector api

A real-world example of a Stream Collector

Java Stream’s Collectors methods fit most use-cases. They allow returning either a Collection or a scalar. For the former, you use one of the toXXX() method, for the latter, one of the reducing() one. Let’s imagine an e-commerce platform that implements a shopping cart. The cart is modeled as the following: This diagram might translate into the following (abridged) code: Product.

Apr 16, 2017 java 8 lambda collector

Custom collectors in Java 8

Among the many features available in Java 8, streams seem to be one of the biggest game changers regarding the way to write Java code. Usage is quite straightforward: the stream is created from a collection (or from a static method of an utility class), it’s processed using one or many of the available stream methods, and the collected back into a collection or an object. One generally uses one of the static method that the Collectors utility class offers: Collectors.toList()Collectors.