Add Java Development Collection and Upgrade Guides
- Created a new collection for Java development, including prompts and instructions for Spring Boot, Quarkus, JPA, JUnit, and Javadoc. - Added comprehensive markdown documentation for upgrading from Java 17 to Java 21, detailing new language features, API changes, and best practices. - Introduced upgrade guide for transitioning from Java 21 to Java 25, highlighting new features, migration strategies, and performance considerations.
This commit is contained in:
Bruno Borges
parent
e8337ea8a0
commit
56a9426dda
@ -20,6 +20,7 @@ Curated collections of related prompts, instructions, and chat modes organized a
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| [Database & Data Management](collections/database-data-management.md) | Database administration, SQL optimization, and data management tools for PostgreSQL, SQL Server, and general database development best practices. | 8 items | database, sql, postgresql, sql-server, dba, optimization, queries, data-management |
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| [DevOps On-Call](collections/devops-oncall.md) | A focused set of prompts, instructions, and a chat mode to help triage incidents and respond quickly with DevOps tools and Azure resources. | 5 items | devops, incident-response, oncall, azure |
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| [Frontend Web Development](collections/frontend-web-dev.md) | Essential prompts, instructions, and chat modes for modern frontend web development including React, Angular, Vue, TypeScript, and CSS frameworks. | 11 items | frontend, web, react, typescript, javascript, css, html, angular, vue |
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| [Java Development](collections/java-development.md) | Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices. | 11 items | java, springboot, quarkus, jpa, junit, javadoc |
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| [Project Planning & Management](collections/project-planning.md) | Tools and guidance for software project planning, feature breakdown, epic management, implementation planning, and task organization for development teams. | 17 items | planning, project-management, epic, feature, implementation, task, architecture, technical-spike |
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| [Security & Code Quality](collections/security-best-practices.md) | Security frameworks, accessibility guidelines, performance optimization, and code quality best practices for building secure, maintainable, and high-performance applications. | 6 items | security, accessibility, performance, code-quality, owasp, a11y, optimization, best-practices |
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| [Technical Spike](collections/technical-spike.md) | Tools for creation, management and research of technical spikes to reduce unknowns and assumptions before proceeding to specification and implementation of solutions. | 2 items | technical-spike, assumption-testing, validation, research |
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@ -1,19 +1,22 @@
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# 📋 Custom Instructions
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Team and project-specific instructions to enhance GitHub Copilot's behavior for specific technologies and coding practices.
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### How to Use Custom Instructions
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**To Install:**
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- Click the **VS Code** or **VS Code Insiders** install button for the instruction you want to use
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- Download the `*.instructions.md` file and manually add it to your project's instruction collection
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**To Use/Apply:**
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- Copy these instructions to your `.github/copilot-instructions.md` file in your workspace
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- Create task-specific `.github/.instructions.md` files in your workspace's `.github/instructions` folder
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- Instructions automatically apply to Copilot behavior once installed in your workspace
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| Title | Description |
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| ----- | ----------- |
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| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| [Instructions for accessibility](instructions/a11y.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fa11y.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fa11y.instructions.md) | Guidance for creating more accessible code |
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| [AI Prompt Engineering & Safety Best Practices](instructions/ai-prompt-engineering-safety-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fai-prompt-engineering-safety-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fai-prompt-engineering-safety-best-practices.instructions.md) | Comprehensive best practices for AI prompt engineering, safety frameworks, bias mitigation, and responsible AI usage for Copilot and LLMs. |
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| [Angular Development Instructions](instructions/angular.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fangular.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fangular.instructions.md) | Angular-specific coding standards and best practices |
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@ -49,6 +52,8 @@ Team and project-specific instructions to enhance GitHub Copilot's behavior for
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| [Gilfoyle Code Review Instructions](instructions/gilfoyle-code-review.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgilfoyle-code-review.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgilfoyle-code-review.instructions.md) | Gilfoyle-style code review instructions that channel the sardonic technical supremacy of Silicon Valley's most arrogant systems architect. |
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| [GitHub Actions CI/CD Best Practices](instructions/github-actions-ci-cd-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgithub-actions-ci-cd-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgithub-actions-ci-cd-best-practices.instructions.md) | Comprehensive guide for building robust, secure, and efficient CI/CD pipelines using GitHub Actions. Covers workflow structure, jobs, steps, environment variables, secret management, caching, matrix strategies, testing, and deployment strategies. |
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| [Go Development Instructions](instructions/go.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgo.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgo.instructions.md) | Instructions for writing Go code following idiomatic Go practices and community standards |
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| [Java 17 to Java 21 Upgrade Guide](instructions/java-17-to-java-21-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.md) | Guide specific coding standards and best practices |
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| [Java 21 to Java 25 Upgrade Guide](instructions/java-21-to-java-25-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.md) | Comprehensive best practices for adopting new Java 25 features since the release of Java 21. |
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| [Java Development](instructions/java.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md) | Guidelines for building Java base applications |
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| [Joyride User Scripts Project Assistant](instructions/joyride-user-project.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-user-project.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-user-project.instructions.md) | Expert assistance for Joyride User Script projects - REPL-driven ClojureScript and user space automation of VS Code |
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| [Joyride Workspace Automation Assistant](instructions/joyride-workspace-automation.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-workspace-automation.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-workspace-automation.instructions.md) | Expert assistance for Joyride Workspace automation - REPL-driven and user space ClojureScript automation within specific VS Code workspaces |
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collections/java-development.collection.yml
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collections/java-development.collection.yml
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id: java-development
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name: Java Development
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description: Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices.
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tags: [java, springboot, quarkus, jpa, junit, javadoc]
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items:
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- path: instructions/java.instructions.md
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kind: instruction
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- path: instructions/springboot.instructions.md
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kind: instruction
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- path: instructions/quarkus.instructions.md
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kind: instruction
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- path: instructions/quarkus-mcp-server-sse.instructions.md
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kind: instruction
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- path: instructions/convert-jpa-to-spring-data-cosmos.instructions.md
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kind: instruction
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- path: instructions/java-17-to-java-21-upgrade.md
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kind: instruction
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- path: instructions/java-21-to-java-25-upgrade.md
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kind: instruction
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- path: prompts/java-docs.prompt.md
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kind: prompt
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- path: prompts/java-junit.prompt.md
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kind: prompt
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- path: prompts/java-springboot.prompt.md
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kind: prompt
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- path: prompts/create-spring-boot-java-project.prompt.md
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kind: prompt
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display:
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ordering: alpha
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show_badge: false
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collections/java-development.md
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collections/java-development.md
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# Java Development
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Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices.
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**Tags:** java, springboot, quarkus, jpa, junit, javadoc
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## Items in this Collection
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| Title | Type | Description |
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| ----- | ---- | ----------- |
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| [Convert Spring JPA project to Spring Data Cosmos](../instructions/convert-jpa-to-spring-data-cosmos.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fconvert-jpa-to-spring-data-cosmos.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fconvert-jpa-to-spring-data-cosmos.instructions.md) | Instruction | Step-by-step guide for converting Spring Boot JPA applications to use Azure Cosmos DB with Spring Data Cosmos |
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| [Create Spring Boot Java project prompt](../prompts/create-spring-boot-java-project.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fcreate-spring-boot-java-project.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fcreate-spring-boot-java-project.prompt.md) | Prompt | Create Spring Boot Java Project Skeleton |
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| [GitHub Copilot Instructions: Java 17 to Java 21 Upgrade Guide](../instructions/java-17-to-java-21-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.md) | Instruction | No description |
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| [GitHub Copilot Instructions: Java 21 to Java 25 Upgrade Guide](../instructions/java-21-to-java-25-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.md) | Instruction | Comprehensive best practices for adopting new Java 25 features since the release of Java 21. |
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| [Java Development](../instructions/java.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md) | Instruction | Guidelines for building Java base applications |
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| [Java Documentation (Javadoc) Best Practices](../prompts/java-docs.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-docs.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-docs.prompt.md) | Prompt | Ensure that Java types are documented with Javadoc comments and follow best practices for documentation. |
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| [JUnit 5+ Best Practices](../prompts/java-junit.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-junit.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-junit.prompt.md) | Prompt | Get best practices for JUnit 5 unit testing, including data-driven tests |
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| [Quarkus](../instructions/quarkus.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus.instructions.md) | Instruction | Quarkus development standards and instructions |
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| [Quarkus MCP Server](../instructions/quarkus-mcp-server-sse.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus-mcp-server-sse.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus-mcp-server-sse.instructions.md) | Instruction | Quarkus and MCP Server with HTTP SSE transport development standards and instructions |
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| [Spring Boot Best Practices](../prompts/java-springboot.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-springboot.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-springboot.prompt.md) | Prompt | Get best practices for developing applications with Spring Boot. |
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| [Spring Boot Development](../instructions/springboot.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fspringboot.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fspringboot.instructions.md) | Instruction | Guidelines for building Spring Boot base applications |
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459
instructions/java-17-to-java-21-upgrade.md
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instructions/java-17-to-java-21-upgrade.md
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# GitHub Copilot Instructions: Java 17 to Java 21 Upgrade Guide
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These instructions help GitHub Copilot assist developers in upgrading Java projects from JDK 17 to JDK 21, focusing on new language features, API changes, and best practices.
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## Major Language Features in JDK 18-21
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### Pattern Matching for switch (JEP 441 - Standard in 21)
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**Enhanced switch Expressions and Statements**
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When working with switch constructs:
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- Suggest converting traditional switch to pattern matching where appropriate
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- Use pattern matching for type checking and destructuring
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- Example upgrade patterns:
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```java
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// Old approach (Java 17)
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public String processObject(Object obj) {
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if (obj instanceof String) {
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String s = (String) obj;
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return s.toUpperCase();
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} else if (obj instanceof Integer) {
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Integer i = (Integer) obj;
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return i.toString();
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}
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return "unknown";
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}
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// New approach (Java 21)
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public String processObject(Object obj) {
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return switch (obj) {
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case String s -> s.toUpperCase();
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case Integer i -> i.toString();
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case null -> "null";
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default -> "unknown";
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};
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}
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```
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- Support guarded patterns:
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```java
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switch (obj) {
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case String s when s.length() > 10 -> "Long string: " + s;
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case String s -> "Short string: " + s;
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case Integer i when i > 100 -> "Large number: " + i;
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case Integer i -> "Small number: " + i;
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default -> "Other";
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}
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```
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|
||||
### Record Patterns (JEP 440 - Standard in 21)
|
||||
|
||||
**Destructuring Records in Pattern Matching**
|
||||
|
||||
When working with records:
|
||||
- Suggest using record patterns for destructuring
|
||||
- Combine with switch expressions for powerful data processing
|
||||
- Example usage:
|
||||
```java
|
||||
public record Point(int x, int y) {}
|
||||
public record ColoredPoint(Point point, Color color) {}
|
||||
|
||||
// Destructuring in switch
|
||||
public String describe(Object obj) {
|
||||
return switch (obj) {
|
||||
case Point(var x, var y) -> "Point at (" + x + ", " + y + ")";
|
||||
case ColoredPoint(Point(var x, var y), var color) ->
|
||||
"Colored point at (" + x + ", " + y + ") in " + color;
|
||||
default -> "Unknown shape";
|
||||
};
|
||||
}
|
||||
```
|
||||
|
||||
- Use in complex pattern matching:
|
||||
```java
|
||||
// Nested record patterns
|
||||
switch (shape) {
|
||||
case Rectangle(ColoredPoint(Point(var x1, var y1), var c1),
|
||||
ColoredPoint(Point(var x2, var y2), var c2))
|
||||
when c1 == c2 -> "Monochrome rectangle";
|
||||
case Rectangle r -> "Multi-colored rectangle";
|
||||
}
|
||||
```
|
||||
|
||||
### Virtual Threads (JEP 444 - Standard in 21)
|
||||
|
||||
**Lightweight Concurrency**
|
||||
|
||||
When working with concurrency:
|
||||
- Suggest Virtual Threads for high-throughput, concurrent applications
|
||||
- Use `Thread.ofVirtual()` for creating virtual threads
|
||||
- Example migration patterns:
|
||||
```java
|
||||
// Old platform thread approach
|
||||
ExecutorService executor = Executors.newFixedThreadPool(100);
|
||||
executor.submit(() -> {
|
||||
// blocking I/O operation
|
||||
httpClient.send(request);
|
||||
});
|
||||
|
||||
// New virtual thread approach
|
||||
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
|
||||
executor.submit(() -> {
|
||||
// blocking I/O operation - now scales to millions
|
||||
httpClient.send(request);
|
||||
});
|
||||
}
|
||||
```
|
||||
|
||||
- Use structured concurrency patterns:
|
||||
```java
|
||||
// Structured concurrency (Preview)
|
||||
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
|
||||
Future<String> user = scope.fork(() -> fetchUser(userId));
|
||||
Future<String> order = scope.fork(() -> fetchOrder(orderId));
|
||||
|
||||
scope.join(); // Join all subtasks
|
||||
scope.throwIfFailed(); // Propagate errors
|
||||
|
||||
return processResults(user.resultNow(), order.resultNow());
|
||||
}
|
||||
```
|
||||
|
||||
### String Templates (JEP 430 - Preview in 21)
|
||||
|
||||
**Safe String Interpolation**
|
||||
|
||||
When working with string formatting:
|
||||
- Suggest String Templates for safe string interpolation (preview feature)
|
||||
- Enable preview features with `--enable-preview`
|
||||
- Example usage:
|
||||
```java
|
||||
// Traditional concatenation
|
||||
String message = "Hello, " + name + "! You have " + count + " messages.";
|
||||
|
||||
// String Templates (Preview)
|
||||
String message = STR."Hello, \{name}! You have \{count} messages.";
|
||||
|
||||
// Safe HTML generation
|
||||
String html = HTML."<p>User: \{username}</p>";
|
||||
|
||||
// Safe SQL queries
|
||||
PreparedStatement stmt = SQL."SELECT * FROM users WHERE id = \{userId}";
|
||||
```
|
||||
|
||||
### Sequenced Collections (JEP 431 - Standard in 21)
|
||||
|
||||
**Enhanced Collection Interfaces**
|
||||
|
||||
When working with collections:
|
||||
- Use new `SequencedCollection`, `SequencedSet`, `SequencedMap` interfaces
|
||||
- Access first/last elements uniformly across collection types
|
||||
- Example usage:
|
||||
```java
|
||||
// New methods available on Lists, Deques, LinkedHashSet, etc.
|
||||
List<String> list = List.of("first", "middle", "last");
|
||||
String first = list.getFirst(); // "first"
|
||||
String last = list.getLast(); // "last"
|
||||
List<String> reversed = list.reversed(); // ["last", "middle", "first"]
|
||||
|
||||
// Works with any SequencedCollection
|
||||
SequencedSet<String> set = new LinkedHashSet<>();
|
||||
set.addFirst("start");
|
||||
set.addLast("end");
|
||||
String firstElement = set.getFirst();
|
||||
```
|
||||
|
||||
### Unnamed Patterns and Variables (JEP 443 - Preview in 21)
|
||||
|
||||
**Simplified Pattern Matching**
|
||||
|
||||
When working with pattern matching:
|
||||
- Use unnamed patterns `_` for values you don't need
|
||||
- Simplify switch expressions and record patterns
|
||||
- Example usage:
|
||||
```java
|
||||
// Ignore unused variables
|
||||
switch (ball) {
|
||||
case RedBall(_) -> "Red ball"; // Don't care about size
|
||||
case BlueBall(var size) -> "Blue ball size " + size;
|
||||
}
|
||||
|
||||
// Ignore parts of records
|
||||
switch (point) {
|
||||
case Point(var x, _) -> "X coordinate: " + x; // Ignore Y
|
||||
case ColoredPoint(Point(_, var y), _) -> "Y coordinate: " + y;
|
||||
}
|
||||
|
||||
// Exception handling with unnamed variables
|
||||
try {
|
||||
riskyOperation();
|
||||
} catch (IOException | SQLException _) {
|
||||
// Don't need exception details
|
||||
handleError();
|
||||
}
|
||||
```
|
||||
|
||||
### Scoped Values (JEP 446 - Preview in 21)
|
||||
|
||||
**Improved Context Propagation**
|
||||
|
||||
When working with thread-local data:
|
||||
- Consider Scoped Values as a modern alternative to ThreadLocal
|
||||
- Better performance and clearer semantics for virtual threads
|
||||
- Example usage:
|
||||
```java
|
||||
// Define scoped value
|
||||
private static final ScopedValue<String> USER_ID = ScopedValue.newInstance();
|
||||
|
||||
// Set and use scoped value
|
||||
ScopedValue.where(USER_ID, "user123")
|
||||
.run(() -> {
|
||||
processRequest(); // Can access USER_ID.get() anywhere in call chain
|
||||
});
|
||||
|
||||
// In nested method
|
||||
public void processRequest() {
|
||||
String userId = USER_ID.get(); // "user123"
|
||||
// Process with user context
|
||||
}
|
||||
```
|
||||
|
||||
## API Enhancements and New Features
|
||||
|
||||
### UTF-8 by Default (JEP 400 - Standard in 18)
|
||||
|
||||
When working with file I/O:
|
||||
- UTF-8 is now the default charset on all platforms
|
||||
- Remove explicit charset specifications where UTF-8 was intended
|
||||
- Example simplification:
|
||||
```java
|
||||
// Old explicit UTF-8 specification
|
||||
Files.readString(path, StandardCharsets.UTF_8);
|
||||
Files.writeString(path, content, StandardCharsets.UTF_8);
|
||||
|
||||
// New default behavior (Java 18+)
|
||||
Files.readString(path); // Uses UTF-8 by default
|
||||
Files.writeString(path, content); // Uses UTF-8 by default
|
||||
```
|
||||
|
||||
### Simple Web Server (JEP 408 - Standard in 18)
|
||||
|
||||
When needing basic HTTP server:
|
||||
- Use built-in `jwebserver` command or `com.sun.net.httpserver` enhancements
|
||||
- Great for testing and development
|
||||
- Example usage:
|
||||
```java
|
||||
// Command line
|
||||
$ jwebserver -p 8080 -d /path/to/files
|
||||
|
||||
// Programmatic usage
|
||||
HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
|
||||
server.createContext("/", new SimpleFileHandler(Path.of("/tmp")));
|
||||
server.start();
|
||||
```
|
||||
|
||||
### Internet-Address Resolution SPI (JEP 418 - Standard in 19)
|
||||
|
||||
When working with custom DNS resolution:
|
||||
- Implement `InetAddressResolverProvider` for custom address resolution
|
||||
- Useful for service discovery and testing scenarios
|
||||
|
||||
### Key Encapsulation Mechanism API (JEP 452 - Standard in 21)
|
||||
|
||||
When working with post-quantum cryptography:
|
||||
- Use KEM API for key encapsulation mechanisms
|
||||
- Example usage:
|
||||
```java
|
||||
KeyPairGenerator kpg = KeyPairGenerator.getInstance("ML-KEM");
|
||||
KeyPair kp = kpg.generateKeyPair();
|
||||
|
||||
KEM kem = KEM.getInstance("ML-KEM");
|
||||
KEM.Encapsulator encapsulator = kem.newEncapsulator(kp.getPublic());
|
||||
KEM.Encapsulated encapsulated = encapsulator.encapsulate();
|
||||
```
|
||||
|
||||
## Deprecations and Warnings
|
||||
|
||||
### Finalization Deprecation (JEP 421 - Deprecated in 18)
|
||||
|
||||
When encountering `finalize()` methods:
|
||||
- Remove finalize methods and use alternatives
|
||||
- Suggest Cleaner API or try-with-resources
|
||||
- Example migration:
|
||||
```java
|
||||
// Deprecated finalize approach
|
||||
@Override
|
||||
protected void finalize() throws Throwable {
|
||||
cleanup();
|
||||
}
|
||||
|
||||
// Modern approach with Cleaner
|
||||
private static final Cleaner CLEANER = Cleaner.create();
|
||||
|
||||
public MyResource() {
|
||||
cleaner.register(this, new CleanupTask(nativeResource));
|
||||
}
|
||||
|
||||
private static class CleanupTask implements Runnable {
|
||||
private final long nativeResource;
|
||||
|
||||
CleanupTask(long nativeResource) {
|
||||
this.nativeResource = nativeResource;
|
||||
}
|
||||
|
||||
public void run() {
|
||||
cleanup(nativeResource);
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### Dynamic Agent Loading (JEP 451 - Warnings in 21)
|
||||
|
||||
When working with agents or instrumentation:
|
||||
- Add `-XX:+EnableDynamicAgentLoading` to suppress warnings if needed
|
||||
- Consider loading agents at startup instead of dynamically
|
||||
- Update tooling to use startup agent loading
|
||||
|
||||
## Build Configuration Updates
|
||||
|
||||
### Preview Features
|
||||
|
||||
For projects using preview features:
|
||||
- Add `--enable-preview` to compiler and runtime
|
||||
- Maven configuration:
|
||||
```xml
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-compiler-plugin</artifactId>
|
||||
<configuration>
|
||||
<release>21</release>
|
||||
<compilerArgs>
|
||||
<arg>--enable-preview</arg>
|
||||
</compilerArgs>
|
||||
</configuration>
|
||||
</plugin>
|
||||
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-surefire-plugin</artifactId>
|
||||
<configuration>
|
||||
<argLine>--enable-preview</argLine>
|
||||
</configuration>
|
||||
</plugin>
|
||||
```
|
||||
|
||||
- Gradle configuration:
|
||||
```kotlin
|
||||
java {
|
||||
toolchain {
|
||||
languageVersion = JavaLanguageVersion.of(21)
|
||||
}
|
||||
}
|
||||
|
||||
tasks.withType<JavaCompile> {
|
||||
options.compilerArgs.add("--enable-preview")
|
||||
}
|
||||
|
||||
tasks.withType<Test> {
|
||||
jvmArgs("--enable-preview")
|
||||
}
|
||||
```
|
||||
|
||||
### Virtual Threads Configuration
|
||||
|
||||
For applications using Virtual Threads:
|
||||
- No special JVM flags required (standard feature in 21)
|
||||
- Consider these system properties for debugging:
|
||||
```bash
|
||||
-Djdk.virtualThreadScheduler.parallelism=N # Set carrier thread count
|
||||
-Djdk.virtualThreadScheduler.maxPoolSize=N # Set max pool size
|
||||
```
|
||||
|
||||
## Runtime and GC Improvements
|
||||
|
||||
### Generational ZGC (JEP 439 - Available in 21)
|
||||
|
||||
When configuring garbage collection:
|
||||
- Try Generational ZGC for better performance
|
||||
- Enable with: `-XX:+UseZGC -XX:+ZGenerational`
|
||||
- Monitor allocation patterns and GC behavior
|
||||
|
||||
## Migration Strategy
|
||||
|
||||
### Step-by-Step Upgrade Process
|
||||
|
||||
1. **Update Build Tools**: Ensure Maven/Gradle supports JDK 21
|
||||
2. **Language Feature Adoption**:
|
||||
- Start with pattern matching for switch (standard)
|
||||
- Add record patterns where beneficial
|
||||
- Consider Virtual Threads for I/O heavy applications
|
||||
3. **Preview Features**: Enable only if needed for specific use cases
|
||||
4. **Testing**: Comprehensive testing especially for concurrency changes
|
||||
5. **Performance**: Benchmark with new GC options
|
||||
|
||||
### Code Review Checklist
|
||||
|
||||
When reviewing code for Java 21 upgrade:
|
||||
- [ ] Convert appropriate instanceof chains to switch expressions
|
||||
- [ ] Use record patterns for data destructuring
|
||||
- [ ] Replace ThreadLocal with ScopedValues where appropriate
|
||||
- [ ] Consider Virtual Threads for high-concurrency scenarios
|
||||
- [ ] Remove explicit UTF-8 charset specifications
|
||||
- [ ] Replace finalize() methods with Cleaner or try-with-resources
|
||||
- [ ] Use SequencedCollection methods for first/last access patterns
|
||||
- [ ] Add preview flags only for preview features in use
|
||||
|
||||
### Common Migration Patterns
|
||||
|
||||
1. **Switch Enhancement**:
|
||||
```java
|
||||
// From instanceof chains to switch expressions
|
||||
if (obj instanceof String s) return processString(s);
|
||||
else if (obj instanceof Integer i) return processInt(i);
|
||||
// becomes:
|
||||
return switch (obj) {
|
||||
case String s -> processString(s);
|
||||
case Integer i -> processInt(i);
|
||||
default -> processDefault(obj);
|
||||
};
|
||||
```
|
||||
|
||||
2. **Virtual Thread Adoption**:
|
||||
```java
|
||||
// From platform threads to virtual threads
|
||||
Executors.newFixedThreadPool(200)
|
||||
// becomes:
|
||||
Executors.newVirtualThreadPerTaskExecutor()
|
||||
```
|
||||
|
||||
3. **Record Pattern Usage**:
|
||||
```java
|
||||
// From manual destructuring to record patterns
|
||||
if (point instanceof Point p) {
|
||||
int x = p.x();
|
||||
int y = p.y();
|
||||
}
|
||||
// becomes:
|
||||
if (point instanceof Point(var x, var y)) {
|
||||
// use x and y directly
|
||||
}
|
||||
```
|
||||
|
||||
## Performance Considerations
|
||||
|
||||
- Virtual Threads excel with blocking I/O but may not benefit CPU-intensive tasks
|
||||
- Generational ZGC can reduce GC overhead for most applications
|
||||
- Pattern matching in switch is generally more efficient than instanceof chains
|
||||
- SequencedCollection methods provide O(1) access to first/last elements
|
||||
- Scoped Values have lower overhead than ThreadLocal for virtual threads
|
||||
|
||||
## Testing Recommendations
|
||||
|
||||
- Test Virtual Thread applications under high concurrency
|
||||
- Verify pattern matching covers all expected cases
|
||||
- Performance test with Generational ZGC vs other collectors
|
||||
- Validate UTF-8 default behavior across different platforms
|
||||
- Test preview features thoroughly before production use
|
||||
|
||||
Remember to enable preview features only when specifically needed and test thoroughly in staging environments before deploying to production.
|
||||
Loading…
x
Reference in New Issue
Block a user