https://foojay.io/today/category/intellij/Recent content in IntelliJ on foojay.io - Friends Of OpenJDKHugoen-usWed, 21 Oct 2026 00:00:00 +0000https://foojay.io/today/java-stream-gatherers/Wed, 21 Oct 2026 00:00:00 +0000https://foojay.io/today/java-stream-gatherers/<h1 id="java-stream-gatherers-from-built-in-patterns-to-custom-pipeline-mechanics">Java Stream Gatherers: From Built-in Patterns to Custom Pipeline Mechanics</h1> <h2 id="table-of-contents">Table of Contents</h2> <ul> <li><a href="#1-introduction--context">1. Introduction &amp; Context</a> <ul> <li><a href="#11-the-evolution-of-streams">1.1 The Evolution of Streams</a></li> <li><a href="#12-the-collector-problem">1.2 The &ldquo;Collector Problem&rdquo;</a></li> <li><a href="#13-what-are-stream-gatherers">1.3 What are Stream Gatherers?</a></li> </ul> </li> <li><a href="#2-getting-started-built-in-gatherers-in-action">2. Getting Started: Built-In Gatherers in Action</a> <ul> <li><a href="#21-understanding-stream-cardinality">2.1 Understanding Stream Cardinality</a></li> <li><a href="#22-the-five-ready-to-use-gatherers">2.2 The Five Ready-to-Use Gatherers</a> <ul> <li><a href="#221-batching-items-with-windowfixed">2.2.1 Batching Items with <code>windowFixed</code></a></li> <li><a href="#222-analyzing-sequences-with-windowsliding">2.2.2 Analyzing Sequences with <code>windowSliding</code></a></li> <li><a href="#223-accumulating-values-with-scan">2.2.3 Accumulating Values with <code>scan</code></a></li> <li><a href="#224-intermediate-aggregations-with-fold">2.2.4 Intermediate Aggregations with <code>fold</code></a></li> <li><a href="#225-bounded-parallelism-with-mapconcurrent">2.2.5 Bounded Parallelism with <code>mapConcurrent</code></a></li> </ul> </li> </ul> </li> <li><a href="#3-leveling-up-from-using-gatherers-to-authoring-your-own">3. Leveling Up: From Using Gatherers to Authoring Your Own</a> <ul> <li><a href="#31-when-should-you-write-a-custom-gatherer">3.1 When Should You Write a Custom Gatherer?</a></li> <li><a href="#32-pipeline-composition-with-andthen">3.2 Pipeline Composition with <code>andThen()</code></a></li> </ul> </li> <li><a href="#4-under-the-hood-architecture--anatomy-of-custom-gatherers">4. Under the Hood: Architecture &amp; Anatomy of Custom Gatherers</a> <ul> <li><a href="#41-anatomy-of-a-gatherert-a-r">4.1 Anatomy of a <code>Gatherer&lt;T, A, R&gt;</code></a></li> <li><a href="#42-the-four-building-blocks-initializer-integrator-combiner-finisher">4.2 The Four Building Blocks (<code>initializer</code>, <code>integrator</code>, <code>combiner</code>, <code>finisher</code>)</a></li> <li><a href="#43-concrete-walkthrough-building-a-custom-gatherer">4.3 Concrete Walkthrough: Building a Custom Gatherer</a></li> </ul> </li> <li><a href="#5-production-ready-gatherers-parallelism-state-and-pitfalls">5. Production-Ready Gatherers: Parallelism, State, and Pitfalls</a> <ul> <li><a href="#51-parallel-execution-modes--combiners">5.1 Parallel Execution Modes &amp; Combiners</a></li> <li><a href="#52-greedy-vs-short-circuiting-integrators">5.2 Greedy vs. Short-Circuiting Integrators</a></li> <li><a href="#53-state-management--thread-safety">5.3 State Management &amp; Thread Safety</a></li> <li><a href="#54-gatherer-vs-collector-a-quick-comparison">5.4 Gatherer vs. Collector: A Quick Comparison</a></li> </ul> </li> <li><a href="#6-conclusion">6. Conclusion</a></li> <li><a href="#references">References</a></li> </ul> <hr> <p><img src="https://foojay.io/today/java-stream-gatherers/StreamGatherers.jpg" alt="Stream Gatherers" title="Stream Gatherers" width="1024" height="559" loading="lazy" decoding="async"></p>