Java Runtime Upgrades
JDK 8 to 17 or 21 migrations with deprecated API refactoring and toolchain updates. Our JVM optimization delivered a 2x faster runtime after moving to JDK 21.
2x faster runtime →Legacy Application Modernization
Legacy Application Modernization Without Business Disruption
Upgrade ageing runtimes, frameworks and architectures in safe, tested steps. Your users keep working while the platform underneath becomes secure, fast and cloud-ready.
- 100+ global brands served
- ISO 9001 & ISO 27001 certified
- JDK 8 to 17 and 21 upgrades delivered
Live product build
simulated demoModernizeOps
JDK 8 → 17 readiness
Tests passing97%
- Deprecated APIs refactored142 of 150
- javax to jakarta importsIn progress · 3 modules
- Unsupported libraryReplace legacy XML parser
app.modernizeops.com
ModernizeOps
JDK 8 → 17 readiness
Tests passing97%
- Deprecated APIs refactored142 of 150
- javax to jakarta importsIn progress · 3 modules
- Unsupported libraryReplace legacy XML parser
- 1Design
- 2Build
- 3Test
- 4Release
⟳ Design in progress
- Faster performance after a JDK 8 to 17 migration
- 40%
- Faster performance after a JDK 8 to 17 migration
- Less technical debt on a Java modernization
- 50%
- Less technical debt on a Java modernization
- Faster runtime after a JDK 8 to 21 upgrade
- 2x
- Faster runtime after a JDK 8 to 21 upgrade
- Outdated packages fixed in a React upgrade
- 186
- Outdated packages fixed in a React upgrade
- Data loss in a phased Elasticsearch upgrade
- Zero
- Data loss in a phased Elasticsearch upgrade
Old systems often still hold the most valuable rules in the business. The risk is that nobody can safely change them anymore. Legacy application modernization keeps those rules and replaces what is holding them back: unsupported runtimes, brittle frameworks and architectures that cannot reach the cloud.
Our team at ICANIO has moved Java applications from JDK 8 to JDK 17 and 21, upgraded React frontends across major versions and replaced ageing integrations. We work in phases, prove behaviour with automated tests and keep production running throughout.
This guide explains the modernization options, how we assess risk, what usually goes wrong and how to measure success. It draws on real ICANIO engagements in insurance, fintech and healthcare.
What Is Legacy Application Modernization?
Legacy application modernization is the process of updating an existing system so it stays secure, supportable and able to grow. It can mean a runtime upgrade, a framework migration, a move to the cloud or a staged rewrite of parts of the code.
A system becomes legacy for many reasons. Its runtime may be out of vendor support. Its libraries may carry known vulnerabilities. Its build tools may not run on modern machines, or the people who wrote it may have left.
Modernization is different from replacement. The goal is to keep proven business logic while removing the constraints around it. That makes it lower risk than a rewrite, but it still needs careful planning.
The work is rarely only technical. Data, integrations, user training and compliance evidence all move with the code. Good legacy application modernization treats each of those as part of the plan.
Working definition
“Legacy application modernization is the phased upgrade of an existing application's runtime, frameworks, architecture or hosting, preserving its business behaviour while restoring security, performance and maintainability.”
Foundations
Principles of Low-Risk Modernization
- 01 →
Behaviour First
We capture what the system does today in characterisation tests before changing a line.
- 02 →
Small, Reversible Steps
Each change ships behind a flag or route, so it can be rolled back in minutes.
- 03 →
Debt With a Budget
We rank debt by business risk and fix the items that block security or delivery first.
- 04 ↺
Cloud-Ready Outcome
Every phase moves the app closer to containers, CI/CD and managed services.
Core capabilities
Legacy Application Modernization Services
Each service targets a different kind of ageing. Many legacy application modernization programmes combine two or three of them.
Frontend Framework Upgrades
React, Angular and JavaScript upgrades with dependency clean-up and test coverage. A healthcare React upgrade from 16.3.1 to 18.3.1 fixed 186 outdated packages.
3x productivity →Integration Replacement
Swapping retired third-party services for supported ones. Our insurance legacy application modernization replaced NIPR with Vertafore alongside a JDK 17 upgrade.
50% less debt →Data Platform Upgrades
Phased upgrades of databases and search clusters with zero data loss. A fintech Elasticsearch move from v7.15 to v8.8.1 covered 1000GB of production data.
Zero data loss →Monolith Decomposition
Strangler fig migrations that move one capability at a time into new services. Legacy application modernization this way avoids a risky big-bang cutover.
Route by route
Cloud Re-Platforming
Containerising applications, adding CI/CD and moving to managed cloud databases. We plan the hosting change together with the code change, so both land cleanly.
Cloud-ready →Architecture
Our Legacy Application Modernization Blueprint
We wrap the legacy system with a safety net first, then replace parts behind a routing layer. Users never see the seams.
01
Assess & Baseline
- Code and dependency scan
- Runtime support status
- Performance baseline
- Business rule inventory
02
Safety Net
- Characterisation tests
- CI pipeline
- Observability
- Rollback plan
03
Transform
- Runtime upgrade
- API refactoring
- Strangler routing
- Data migration
04
Operate & Retire
- Parallel run
- Traffic cutover
- Legacy decommission
- Runbooks and handover
Closed-loop feedback: Performance and error data from each phase feed the next. If a step regresses, we roll back and fix it before moving on.
Challenges we solve
Why Modernization Projects Fail
Most failed upgrades share a handful of causes. We design each legacy application modernization plan to avoid them.
- 01
The Big-Bang Rewrite
Rewriting everything at once freezes features for years. We modernise in slices that deliver value as they go.
- 02
Unknown Business Rules
Old code hides rules nobody documented. We extract them through tests and expert reviews before refactoring.
- 03
Dependency Dead Ends
Some libraries have no supported version. We find replacements early, before they block the upgrade.
- 04
Testing Too Late
Toolchain issues found at the end cause delays. We modernise the build and test setup first.
- 05
Data Treated as Simple
Migrations fail on edge-case records. We rehearse data moves on production-like copies.
- 06
No Retirement Date
Running old and new forever doubles cost. We set a clear decommission milestone.
Modernization Strategies Explained
Industry frameworks list several strategies, often called the Rs. These four cover most legacy application modernization work.
- 1Rehost: Move the application to new infrastructure, such as the cloud, with minimal code change. Fast, but it keeps old debt.
- 2Replatform: Upgrade the runtime or database and containerise, keeping the core design. Our JDK upgrades fit here.
- 3Refactor or re-architect: Restructure code, often into services, to unlock scale and faster delivery. Usually done with the strangler fig pattern.
- 4Rebuild or replace: Rewrite a component or adopt a product when the old code has little left worth saving.
Rehost vs Replatform vs Refactor
Each path trades speed for long-term benefit. We recommend mixing them across components.
| Criterion | Rehost | Replatform | Refactor |
|---|---|---|---|
| Speed to complete | Fast | Medium | Slow |
| Removes technical debt | No | Partial | ✓ Yes |
| Fixes unsupported runtime | No | ✓ Yes | ✓ Yes |
| Enables microservices | No | Partial | ✓ Yes |
| Best for | Data centre exits | Ageing runtimes | Core systems that must evolve |
Benefits of Legacy Application Modernization
Modern platforms are cheaper to run and safer to change.
- Stronger securityBecause supported runtimes and libraries receive patches again.
- Better performanceBecause modern JVMs and frameworks are faster out of the box.
- Lower maintenance costBecause deprecated code and workarounds are removed.
- Easier hiringBecause engineers want to work on current technology.
- Cloud readinessBecause containerised apps can use managed services and autoscaling.
- Faster deliveryBecause CI/CD and tests make every future change safer.
Delivery
Our Legacy Application Modernization Process
Week 1–3
Assessment
Code, dependency and infrastructure audit, with a risk-ranked roadmap and effort estimate.
Week 3–5
Safety Net
Characterisation tests, CI pipeline and monitoring set up around the current system.
Week 5–14
Phased Upgrade
Runtime, framework and API changes delivered in small releases behind flags or routes.
Week 12–16
Parallel Run
Old and new paths compared on live traffic until outputs match, then traffic is switched.
Ongoing
Retire & Sustain
Legacy components decommissioned, documentation handed over and a regular upgrade cadence agreed.
Case study
Case Study: Java Modernization to JDK 17
A legacy Java application on JDK 8 faced security risks, compliance issues and incompatibility with modern build tools and cloud platforms. ICANIO migrated it to JDK 17, refactored deprecated APIs, updated the toolchain and ran comprehensive testing. The result was 40% better performance, 3x stronger security compliance, 50% less technical debt and a cloud-ready platform.
Read the full case study →01
Compatibility Analysis
JDK 8 → 17
Version-specific issues were found and fixed in code before they reached production.
02
API Refactoring
Deprecated API removal
Deprecated APIs were aligned with JDK 17 standards, which made the debt reduction stick.
03
Toolchain & Testing
Modern build tools
The development environment was updated first, so testing matched real production conditions.
More App Development Services
Specialist services within our mobile & web application development practice.
- Main serviceMobile & Web Application Development →Scalable, secure web and mobile apps crafted for performance and user excellence.
- Custom Software Development →Bespoke business software designed around your workflows, not a vendor's roadmap.
- Web & Mobile App Development →Responsive web apps and native or cross-platform mobile apps from UX to app store.
- SaaS Development →Multi-tenant SaaS products with billing, onboarding and scale designed in from day one.
- API Development Services →Secure, documented APIs and integrations that connect your systems and partners.
- CMS Development →TYPO3, Liferay and headless CMS builds, upgrades and migrations for content-heavy sites.
- Custom CRM Development →CRMs, employee portals and workforce platforms tailored to how your teams actually work.
- Custom ERP Development →ERP platforms and business portals for finance, sales, inventory, manufacturing, projects and HR, built around your processes.
- Software Testing Services →Functional, performance, security and automated testing that makes releases production-ready.
- Dedicated Development Team →A long-term ICANIO engineering team that owns outcomes as an extension of yours.
Choosing a Modernization Partner
Modernization rewards patience and precision. Look for these five qualities.
- 1Proven upgrades. Ask for completed runtime or framework migrations with measured results.
- 2Test-first habits. The partner should build a safety net before touching the code.
- 3Phased plans. Avoid anyone who proposes a single cutover for a core system.
- 4Data discipline. Check how they rehearse and verify data migrations.
- 5Knowledge transfer. Make sure documentation and runbooks are part of the deliverables.
Our team treats every legacy application modernization as a sequence of small wins. Each release reduces risk and proves the next step is safe.
Security and Compliance During Modernization
Unsupported runtimes are one of the most common audit findings. Moving to a current long-term support release restores vendor patches and closes known vulnerabilities.
ICANIO works under ISO 9001 and ISO 27001 certified processes. During legacy application modernization we add dependency scanning, an SBOM and secrets management to the new pipeline.
For regulated clients we keep evidence of each change, test result and data verification. That record helps when auditors ask how the upgrade was controlled.
Building the Business Case
Start with the cost of standing still. Extended support fees, security exceptions, slow releases and hard-to-hire skills all have a price.
Then add the gains. Our Java modernization delivered 40% faster performance and cut technical debt by half. Faster runtimes often reduce hosting cost, and cleaner code speeds up every future feature.
We recommend measuring a few baselines before work starts, such as response time, deployment frequency and incident count. Comparing them after each phase shows the return of legacy application modernization in your own data.
Technology stack
Tools We Use to Modernise
We combine automated migration tooling with careful manual engineering.
Java
JDK 17 and 21Spring BootJakarta EEOpenRewrite
Frontend
- Angular
- TypeScript
React 18Vite
.NET
- .NET 8
- ASP.NET Core
EF Core
Data
- PostgreSQL
- SQL Server
- Elasticsearch
Flyway
Quality
- SonarQube
JUnitPlaywrightDependency scanning
Platform
- Docker
- Kubernetes
- AWS
- Azure
Inside Our Modernization Work
Legacy Application Modernization FAQs
How long does legacy application modernization take?
A focused runtime upgrade can take a few months. Larger re-architecture programmes run in phases over a longer period. Our assessment gives you a phased roadmap with effort for each step.
Can we modernise without downtime?
Usually, yes. We use feature flags, strangler routing and parallel runs, so users stay on a working system while parts are replaced underneath.
Is it better to rewrite or modernise our application?
Modernising keeps proven business logic and lowers risk. A rewrite makes sense only when little of the old code is worth keeping. Many projects mix both by component.
Why upgrade from JDK 8 to JDK 17 or 21?
Newer long-term support releases bring security updates, better garbage collection and modern language features. Our JDK upgrades improved both performance and security compliance.
What does legacy application modernization cost?
Cost depends on code size, test coverage, dependencies and data. We fix the price of the assessment, then estimate each phase so you can fund the work in stages.
Can legacy application modernization include AI features?
Yes. Once the platform is modern, adding machine learning, smart search or document automation becomes much easier. We often plan these as later phases.
App Development by Industry
How we deliver legacy application modernization and the wider app development practice in each sector.
- ManufacturingApp Development for Manufacturing →Smart factories, connected lines and predictive maintenance.
- Transportation & LogisticsApp Development for Logistics →Fleet health, route optimisation and supply chain visibility.
- Healthcare & Life SciencesApp Development for Healthcare →Clinical platforms, medical AI and HIPAA-ready systems.
- Retail & E-CommerceApp Development for Retail →Commerce platforms, shelf intelligence and demand forecasting.
- Fintech & BankingApp Development for Fintech →Payments, reporting portals and secure data platforms.
- Education & E-LearningApp Development for Education →Learning platforms, placement portals and AI assessment.
Related Specialist Services
- Data & AIData Engineering Services →Pipelines, data lakes and warehouses that turn scattered sources into trusted, AI-ready data.
- DevOps & CloudDevSecOps Services →Security scanning, policy and secrets management built into every pipeline stage.
- AgenticOpsIntelligent Workflow Automation →Workflows that read, decide and act, going beyond rule-based RPA scripts.
Key Takeaways
- Legacy application modernization keeps proven business logic while removing what holds it back.
- Build a test safety net before changing runtimes, frameworks or architecture.
- Modernise in small, reversible phases instead of one big cutover.
- Set a retirement date for legacy components to stop paying for two systems.
Conclusion
Ageing software does not have to be a choice between risky rewrites and growing exposure. Legacy application modernization offers a middle path that protects the business while restoring speed and security.
ICANIO has delivered JDK, React, search and integration upgrades for clients in insurance, fintech and healthcare. The method is consistent: assess, protect, transform in phases and retire the old.
If an unsupported runtime or a fragile codebase worries you, contact us. We will assess your system and propose a practical legacy application modernization roadmap.
By ICANIO Application Engineering Team · Published · Updated
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