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Learn how to use GitHub Copilot agent mode to modernize legacy Java projects with guided upgrades, automated fixes, and cloud-ready migrations.
Whether you’re migrating your app to the cloud or updating Java runtime, modernizing legacy applications is rarely simple. Conflicting or deprecated dependencies, antiquated deployment targets, and lingering security vulnerabilities often block smooth progress.
That’s when GitHub Copilot agent mode, paired with the GitHub Copilot app modernization VS Code extension, comes in. This toolset delivers an interactive, step-by-step experience to help you upgrade and migrate your Java projects faster, with fewer errors and more confidence.
While this guide highlights Java modernization, we also support end-to-end .NET app modernization within Visual Studio through GitHub Copilot Agent Mode. This includes AI-assisted .NET upgrades, cloud-ready migration paths, and seamless deployment to Azure — delivering a consistent, guided experience across the entire modernization journey that reduces manual effort and accelerates time to value. Learn more in the docs.
In this article, you’ll learn how to use these tools together in Visual Studio Code to:
It’s an advanced feature of GitHub Copilot that transforms the tool from a passive suggestion generator into an active coding collaborator.
It’s like having a junior developer on your team who understands what you’re trying to achieve and works through multiple steps to make it happen, automatically and iteratively, without you having to spell out every single instruction.
Copilot agent mode can:
The flowchart illustrates how Copilot agent mode connects a user’s prompt to a real-time feedback loop, where the agent interacts with your code, workspace, tools, and a large language model (LLM) to continuously plan, act, and refine its solutions.
Learn more about Copilot agent mode >
To follow along, make sure you have:
Got it? Now let’s dive into the good stuff.
When you start an agent session using the Java upgrade extension, Copilot performs the following:
Use a sample legacy Java project (or your own), with source control initialized using Git and a working test suite (ideally with unit tests).
Launch the GitHub Copilot chat sidebar and start a new agent session. Choose GitHub Copilot app modernization – upgrade for Java from the available tools.
Copy and paste this inside your agent session to begin:
Copilot will analyze your project and propose an upgrade plan. The tool begins with a scan of your:
It then creates a structured upgrade plan, editable in the Copilot chat. You can prompt Copilot to exclude modules from this upgrade or make any necessary adjustments to the plan.
Once you approve the plan, Copilot begins upgrading files, adjusting imports, and fixing syntax errors. If build errors pop up, Copilot enters a fix-and-test loop until the project compiles cleanly.
Copilot produces a detailed upgrade report, including:
Example code changes before and after the upgrade:
To make the app Azure-ready, you can run an app assessment to identify cloud readiness issues. From the GitHub Copilot app modernization extension UI, click on Migrate to Azure.
Depending on the deployment target, GitHub Copilot app modernization will identify cloud migration issues with recommended actions. To set the deployment target, modify the assessment-config.yaml file under the appmod-java/appcat folder. In this example, we will choose Azure Kubernetes Service (AKS) as the target. (Other deployment targets include Azure App Service, Azure App Service Managed Instance, Azure Container Apps, Azure Kubernetes Service, and AKS Automatic, etc.)
An assessment report is generated, detailing cloud readiness issues. Click on the migrate button associated with the Auth Migration issue category to move from on-premise user authentication to Microsoft Entra ID.
Similar to the upgrade process, Copilot first makes a plan highlighting the dependency updates and configuration changes. Once you approve the plan, Copilot will go ahead and execute the migration steps.
Copilot summarizes a list of changes made for this migration scenario. These changes include:
With your code updated, it’s time to confirm everything works as expected. Copilot will guide you through running your test suite using your project’s build system.
For Maven projects, you can also run tests manually with:
bash
For Gradle projects:
bash
If there are failures, Copilot will help debug or even write missing tests based on your recent changes. All with the human-in-the-loop principle, who has to confirm all proposed steps.
GitHub Copilot app modernization automatically performs comprehensive CVE scanning across all changed dependencies, a critical security feature consistently requested by development teams. When vulnerabilities are detected, the agent intelligently proposes safe version replacements or recommends alternative libraries to maintain security compliance.
Deploying the app to Azure can be a long, painstaking process, and requires a specific set of skills to craft infrastructure as code. We’ve simplified this step and automated deployment to Azure, so you can go from code to cloud faster.
And that’s it. With GitHub Copilot app modernization, you can take a legacy Java project and make it cloud ready. It remediates code for Java upgrades and migrations scenarios, resolves build issues, validates changes, and even helps strengthen test coverage — all within a single, guided workflow.
Whether you’re modernizing Java, upgrading .NET, or planning your next migration, these extensions that enhance Copilot agent mode are ready to help you analyze large codebases, plan upgrades or migrations, fix issues automatically, and save hours of manual debugging.
To get started, modernize your Java and .NET apps, or learn more about the latest AI-assisted modernization enhancements from Azure.
