stay-learning

Whether you're up or down, just StayLearning.

An index of learning examples to help friends.

Each repository isolates a specific library, API, or technique and demonstrates it with minimal, runnable examples.

This document is designed to serve as a navigable index for humans, LLMs, and MCP tools.

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Table of Contents

• stay-learning
  • Table of Contents
  • How to Use This Index
  • Repository Index
    • st-learning-java-streams
    • st-learning-java-arenas
    • st-learning-java-spi
    • st-learning-java-jpms [private]
    • st-learning-java-mapstruct
    • st-learning-java-jackson
    • st-learning-java-base [private]
  • Quick Reference
  • For LLMs and MCP Tools
    • Machine-readable repo list

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How to Use This Index

• Each entry below describes one repository, its purpose, and the key concepts it demonstrates.
• All repositories follow the naming convention st-learning-java-<topic>
• Repositories marked [private] require access rights.
• The base template repository is st-learning-java-base — use it to bootstrap new examples.

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Repository Index

st-learning-java-streams

Topics: java streams collections functional-programming collectors

A collection of small, paired examples demonstrating the Java Streams API versus traditional (pre-stream) loop-based approaches. Each example shows the manual solution alongside the concise Stream equivalent.

Packages and examples:

Package	Concept	Example class
streams.filter	Filtering with Stream.filter	FilterExample
streams.map	Transformation with Stream.map	MapExample
streams.group	Grouping with Collectors.groupingBy	GroupExample
streams.flatmap	Flattening with Stream.flatMap	FlatMapExample
streams.reduce	Aggregation/reduction	ReduceExample
streams.find	Finding with findFirst()	FindExample
streams.collectors	Counting, toMap, joining, partitioning, averaging, summarizing, downstream collectors	CountingExample, ToMapExample, JoiningExample, PartitionExample, AveragingExample, SummarizingExample, DownstreamExample

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st-learning-java-arenas

Topics: java memory arenas foreign-memory jdk24 java.lang.foreign

Demonstrates native memory allocation and management using Java's java.lang.foreign API — specifically Arena and MemorySegment. Shows how to allocate, write, read, and free off-heap native memory.

Key class: com.bhf.learning.memory.ArenaExample

Requirements: JDK 21+ (tested on JDK 24)

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st-learning-java-spi

Topics: java spi service-provider-interface serviceloader design-patterns extensibility

Demonstrates the Java Service Provider Interface (SPI) mechanism using ServiceLoader. Uses an IdentifierProvider interface with two implementations (RandomUuidProvider, TimestampIdProvider) and a factory that selects a provider via system property, environment variable, or ServiceLoader fallback.

Key classes:

• Interface: com.bhf.learning.spi.IdentifierProvider
• Implementations: RandomUuidProvider (uuid), TimestampIdProvider (timestamp)
• Factory: com.bhf.learning.spi.IdentifierProviderFactory

Programmatic usage:

IdentifierProvider p = IdentifierProviderFactory.loadFromConfig();
System.out.println(p.name() + " -> " + p.id());

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st-learning-java-jpms [private]

Topics: java jpms jlink modules gradle docker java21

A multi-module Gradle project demonstrating the Java Platform Module System (JPMS) and JLink for creating a minimal custom Java runtime image. Shows module-info.java usage across modules, inter-module dependencies, and Docker packaging.

Module structure:

Module	Purpose
common	Shared utilities and logger
messages	Message types and entities (Java Records)
domain	Domain logic; depends on common and messages
application	Entry point, wires modules, configured for JLink

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st-learning-java-mapstruct

Topics: java mapstruct object-mapping dto records enums gradle-kotlin-dsl junit5

Demonstrates common MapStruct mapping patterns and recipes with JUnit 5 tests.

Examples:

Example	Concept
Basic	PersonEntity → PersonDTO simple mapping
Record	Mapping to a Java record-based DTO
Enum	Mapping between different enum types (external → domain)
Source property	Property-style accessors (firstName()) on source
Target property	Property-style accessors on target with @AfterMapping
Iterable	Iterable<Item> source → List<ItemDTO> target

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st-learning-java-jackson

Topics: java jackson json serialization deserialization streaming polymorphic

Small learning examples for Jackson mapping, including basic POJO mapping, nested objects, Java Time mapping, streaming capabilities (NDJSON), and polymorphic mapping.

Key classes / examples:

• Person, PersonSample - Basic POJO serialization/deserialization
• Order, Item, OrderSample - Nested objects and Java Time mapping
• StreamingSample - Writing and reading newline-delimited JSON (NDJSON) using Jackson's streaming APIs
• PolymorphicSample - Polymorphic mapping using @JsonTypeInfo and @JsonSubTypes with Animal (Dog, Cat)

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st-learning-java-base [private]

Topics: java gradle template starter

A minimal starter template used to bootstrap new st-learning example repositories. Contains the base Gradle build setup for small Java learning projects. Use this as the starting point when creating a new topic repository.

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Quick Reference

Repository	Topics	Access
st-learning-java-streams	Streams, Collectors, Functional	Public
st-learning-java-arenas	Foreign Memory, Arenas, JDK 24	Public
st-learning-java-spi	SPI, ServiceLoader, Extensibility	Public
st-learning-java-jpms	JPMS, JLink, Multi-module, Docker	Private
st-learning-java-mapstruct	MapStruct, DTO mapping, Records	Public
st-learning-java-jackson	Jackson, JSON, Serialization	Public
st-learning-java-base	Starter template	Private

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For LLMs and MCP Tools

This index repository exists at https://github.com/bhf/st-learning. To access a specific example repository:

1. List all repos in this family: Search GitHub for org:bhf st-learning or user:bhf st-learning.
2. Navigate to a topic: Use the table above to identify the relevant repo, then fetch its README or source files directly.
3. Clone and run: Each repo uses Gradle and can be built with ./gradlew build or ./gradlew test. Private repos require authentication.
4. Language/runtime: All repos use Java (JDK 21+) and Gradle (Kotlin or Groovy DSL).

Machine-readable repo list

The full index is available as st-learning-index.json.