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* Initialize microservices-messaging Spring Boot project Add initial project structure for microservices-messaging using Spring Boot. Includes Maven configuration with dependencies for Kafka, Lombok, and testing, as well as main application, test class, and application properties. * Initialize microservices messaging pattern 1. Added initial project structure for demonstrating the microservices messaging pattern. 2. Introduced service stubs (OrderService, InventoryService, PaymentService, NotificationService), a Message and MessageBroker class, and a main App entry point. 3. Added README and logging configuration. * Implement Message and MessageBroker classes 1. Added the Message class with unique ID, content, and timestamp fields, and a toString method. 2. Implemented the MessageBroker class to support topic-based publish-subscribe messaging, including subscriber management, message publishing, and logging. * Implement messaging pattern for microservices 1. Added message handling logic to InventoryService, PaymentService, and NotificationService. 2. OrderService now publishes order events to a MessageBroker, and App demonstrates the messaging workflow. 3. Each service processes relevant order events and logs actions for demonstration purposes. * Expand microservices messaging docs and add diagrams 1. Enhanced the README with detailed explanations, real-world examples, Java code samples, and references for the Microservices Messaging pattern. 2. Added flowchart and sequence diagram images to illustrate the pattern. * Refactor to use Kafka for microservices messaging 1. Added Apache Kafka for asynchronous communication between services. 2. Added KafkaMessageProducer and KafkaMessageConsumer classes, updated service implementations and main application logic to use Kafka, and adjusted the Maven configuration to include Kafka and Jackson dependencies. 3. Updated and moved all classes to the com.iluwatar.messaging package, improved documentation, and updated diagrams to reflect the new architecture. * Add unit tests and license headers to messaging module 1. Added comprehensive unit tests for App, InventoryService, KafkaMessageConsumer, KafkaMessageProducer, Message, NotificationService, OrderService, and PaymentService. 2. Added MIT license headers to all main source files and logback.xml. 3. Updated pom.xml to include JUnit Jupiter as a test dependency. * Refactor and simplify service and Kafka test classes 1. Simplified unit tests for InventoryService, NotificationService, and PaymentService by removing null content tests and adding instantiation checks. 2. Refactored KafkaMessageConsumerTest and KafkaMessageProducerTest to avoid requiring a real Kafka instance, focusing on class structure and method existence instead of integration behavior. * Add microservices-messaging module and run scripts Introduce the microservices-messaging module and register it in the root pom.xml. Add docker-compose.yml to run a local Kafka (confluentinc/cp-kafka) with a healthcheck, plus run-app.ps1 and run-app.sh helper scripts that start Kafka if needed and then launch the application. Update the module README with usage instructions. Also remove a duplicated junit-jupiter-api test dependency from the module pom to rely on project defaults. * microservices-messaging: code style and Lombok Add Lombok as a provided dependency and apply formatting/refactoring across the microservices-messaging module. Changes include import reordering, Javadoc and logging formatting, consistent lambda/try/catch indentation, small Kafka consumer/producer refinements (Duration/Properties usage and callback formatting), Message class tweaks (@Getter, JSON ctor and toString formatting) and EOF/newline fixes. Unit tests were also reformatted for consistency. These are non-functional style and readability improvements; no behavior changes intended. * Make Kafka producer/consumer testable Refactor KafkaMessageProducer and KafkaMessageConsumer to depend on the Producer/Consumer interfaces and add constructors that accept mockable instances. Extract default producer/consumer creation into factory methods so tests can inject MockProducer/MockConsumer. Update tests across the microservices-messaging module to use MockProducer/MockConsumer, add more meaningful assertions, error/interrupt handling tests, and simplify AppTest. These changes improve unit testability and remove the need for a running Kafka instance while preserving runtime behavior. * Format test Javadoc and reorder imports Normalize Javadoc formatting and reorder static JUnit imports for consistency in messaging tests. Converted multi-line test Javadocs to single-line comments and adjusted import ordering in the following files: - microservices-messaging/src/test/java/com/iluwatar/messaging/KafkaMessageConsumerTest.java - microservices-messaging/src/test/java/com/iluwatar/messaging/KafkaMessageProducerTest.java - microservices-messaging/src/test/java/com/iluwatar/messaging/OrderServiceTest.java No functional changes. * Add MIT headers and exclude .ps1 from license checks Add MIT license headers to microservices-messaging/docker-compose.yml, run-app.ps1 and run-app.sh to ensure license text is present in these scripts. Update root pom.xml to exclude PowerShell (*.ps1) files from the license plugin checks so those files are not processed by the license rule. * Add Kafka docker service to CI workflows Bring up Kafka for tests in CI and PR workflows. Adds steps to run docker compose for microservices-messaging, poll Kafka readiness (up to 20 retries), and always tear down with docker compose down. Enables Maven tests that depend on Kafka. Affects .github/workflows/maven-ci.yml and .github/workflows/maven-pr-builder.yml. * Use kafka-topics instead of kafka-topics.sh Replace calls to kafka-topics.sh with kafka-topics in CI workflows and the Docker Compose healthcheck. Updated .github/workflows/maven-ci.yml, .github/workflows/maven-pr-builder.yml, and microservices-messaging/docker-compose.yml to use the kafka-topics binary for readiness checks and healthchecks. This prevents failures on images that expose the kafka-topics command without the .sh wrapper. * Use docker compose --wait for Kafka startup Replace the custom bash readiness loop with `docker compose ... up -d --wait` in CI and PR workflows. This simplifies startup of the microservices-messaging Kafka service and removes the manual retry/polling logic. Files changed: .github/workflows/maven-ci.yml, .github/workflows/maven-pr-builder.yml. Note: requires a Docker Compose version that supports the `--wait` flag. * Reformat tests for readability Reformatted KafkaMessageConsumerTest and PaymentServiceTest for readability and consistent formatting: reflowed constructor invocation, expanded anonymous HashMap and schedulePollTask lambda blocks, and aligned assertDoesNotThrow parameters. These are pure style changes with no behavioral modifications. * Remove Kafka Docker Compose steps from CI Removed the Start/Stop Kafka Docker Service steps that ran docker compose for microservices-messaging from .github/workflows/maven-ci.yml and .github/workflows/maven-pr-builder.yml. Workflows no longer start or tear down the Kafka docker-compose service during CI/PR runs; other steps (xvfb install, Maven build, Codecov upload, Sonar cache) remain unchanged. * Bump google-java-format to 1.27.0; tidy tests Update pom.xml to use google-java-format 1.27.0 (was 1.17.0). Make minor formatting cleanups in KafkaMessageConsumerTest and PaymentServiceTest by collapsing multi-line calls into single lines. No functional changes. * Downgrade Google Java Format to 1.17.0 Update Spotless googleJavaFormat version in root pom.xml from 1.27.0 to 1.17.0 * Improve Kafka producer and consumer tests Enhance microservices-messaging tests: add consumer tests to verify run() exits immediately when stopped and gracefully handles a WakeupException (ensuring the MockConsumer is closed). Update producer error test to avoid try-with-resources, assert publish behavior and history, trigger failingProducer.errorNext(...) before closing to cover the error callback branch, then close and assert the mock producer is closed. * Refactor App.run and add messaging tests Extract App.run(...) and introduce a package-private sleepMs field to control sleep durations so the demo can be exercised programmatically and sped up for tests. Main now delegates to run; consumers are started there. Tests updated: AppTest sets sleepMs to 0 and adds testRunWithMockObjects using MockProducer/MockConsumer to exercise run without a Kafka broker; KafkaMessageProducerTest adds a null-message publish test; minor formatting fix in KafkaMessageConsumerTest. These changes improve testability and coverage for the microservices-messaging module.
Design Patterns Implemented in Java
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Introduction
Design patterns are the best, formalized practices a programmer can use to solve common problems when designing an application or system.
Design patterns can speed up the development process by providing tested, proven development paradigms.
Reusing design patterns helps prevent subtle issues that cause major problems, and it also improves code readability for coders and architects who are familiar with the patterns.
Getting Started
This site showcases Java Design Patterns. The solutions have been developed by experienced programmers and architects from the open-source community. The patterns can be browsed by their high-level descriptions or by looking at their source code. The source code examples are well commented and can be thought of as programming tutorials on how to implement a specific pattern. We use the most popular battle-proven open-source Java technologies.
Before you dive into the material, you should be familiar with various Software Design Principles.
All designs should be as simple as possible. You should start with KISS, YAGNI, and Do The Simplest Thing That Could Possibly Work principles. Complexity and patterns should only be introduced when they are needed for practical extensibility.
Once you are familiar with these concepts you can start drilling down into the available design patterns by any of the following approaches:
- Search for a specific pattern by name. Can't find one? Please report a new pattern here.
- Using tags such as
Performance,Gang of FourorData access. - Using pattern categories,
Creational,Behavioral, and others.
Hopefully, you find the object-oriented solutions presented on this site useful in your architectures and have as much fun learning them as we had while developing them.
How to Contribute
If you are willing to contribute to the project you will find the relevant information in our developer wiki. We will help you and answer your questions in the Gitter chatroom.
The Book
The design patterns are now available as an e-book. Find out more about "Open Source Java Design Patterns" here: https://payhip.com/b/bNQFX
The project contributors can get the book for free. Contact the maintainer via Gitter chatroom or email (iluwatar (at) gmail (dot) com ). Send a message that contains your email address, Github username, and a link to an accepted pull request.
License
This project is licensed under the terms of the MIT license.
