Untangling Spring Dependencies in Legacy Environments

For development teams in charge of legacy Spring environments, the most significant risk to application stability is the libraries they inherited years ago. Lurking within build files, Spring dependencies form a complex web that can compromise security, compliance, and compatibility if left unmanaged.

With the most recent major releases for Spring Framework and Spring Boot, the Spring ecosystem shifted to a time-based release model aligned with Java's six-month cadence. While this change accelerates innovation and supports cloud-native development, it places immense pressure on organizations maintaining legacy applications. Keeping up with the rapid Spring lifecycle requires a mature build infrastructure and rigorous automated testing, which some teams do not have.

In this blog, we'll discuss how to manage Spring dependencies and maintain operational resilience in legacy environments. We'll also address common migration difficulties and options that prioritize stability and security in between upgrades. 

The Impact of Spring's Rapid Evolution

The transition to a six-month release cycle offers clear benefits for modern development: predictable schedules, faster delivery of improvements, and rapid adoption of new Java features. However, for teams managing legacy systems, this cadence presents a distinct set of challenges.

Because Spring releases are now aligned with OpenJDK, the support window for community versions is relatively short, typically just 12 to 18 months. If an organization requires three to six months to test and validate a new version before deployment, they effectively receive only one year of community support for any given release. Once that window closes, the application is left without security patches or bug fixes.

For enterprises with strict governance processes or heavy validation requirements, this timeline may not be feasible. For applications without continuous integration and continuous delivery build automation, keeping pace with the new Spring release cadence will almost certainly be unachievable. The result: an accumulation of technical debt and dependency drift.

Dependency Management Challenges in Legacy Spring Apps

The risk in legacy Spring applications is rarely confined to the application code itself. The real danger lies in the transitive dependencies — libraries that are indirectly pulled into the project because direct dependencies rely on them. OpenLogic recently presented a webinar on this topic that goes into more depth than this article - you can access it on demand below.

The Ripple Effect of Transitive Dependencies

One outdated dependency can cascade into a series of critical issues. For example, Hibernate versions that are incompatible with new Spring ORMs or older embedded Tomcat versions that reject new Spring Boot.

This "ripple effect" complicates upgrades significantly. Updating a single dependency often necessitates updating multiple underlying libraries, such as Java Architecture for XML Binding (JAXB), Elasticsearch, or Jetty. 

Common issues arising from this web of dependencies include:

• Deprecated APIs: When moving from older Spring versions, some APIs disappear. Examples: WebSecurityConfigurerAdapter removed from Spring Security 5.7+, RestTemplate deprecated in favor of  WebClient (Reactor), and @RequestMapping overuse replaced by dedicated annotations (i.e. @GetMapping, @PostMapping)
• Security Vulnerabilities: Exposure to known CVEs, such as Remote Code Execution (RCE) or Denial of Service (DoS) flaws.
• Build Instability: Unresolvable version conflicts that break compilation.
• Runtime Errors: Issues like NoSuchMethodError or ClassNotFoundException appearing in logs due to mismatched library versions.

All of these issues mean that your application is exposed to security threats even if the core framework appears up to date.

Javax to Jakarta Namespace Shift

A major hurdle for legacy migrations is the namespace shift introduced in Jakarta EE 9. Spring Framework 6.x and Spring Boot 3.x have moved from the javax namespace to the jakarta namespace.

This is not a simple find-and-replace operation. Not all javax packages have been migrated to Jakarta (for instance, javax.transaction.xa remains unchanged). Furthermore, upgrading Spring framework dependencies to version 6.x requires a baseline of JDK 17. If an application relies on third-party libraries that have not yet updated to the Jakarta namespace, the migration path becomes blocked, forcing teams to either wait for vendor updates or fork the library themselves.

Incompatibility with newer Java versions

Upgrading community-based Spring and the JDK must happen in tandem. Using an incompatible Java version can lead to an UnsupportedClassVersionError at runtime.

• Spring Framework 5.3: Supports JDK 8-21.
• Spring Framework 6.x: Requires a minimum of JDK 17.

If a major point upgrade of Spring is performed without upgrading the JDK, organizations face incompatible dependency versions and missing classes. This tight coupling between the framework and the runtime environment means that a Spring upgrade often turns into a comprehensive platform upgrade, requiring significant planning and resources.

The Security Risks of Inaction

Running on end-of-life (EOL) versions of Spring is a calculated risk that often backfires. Once a version reaches EOL, the open source community stops providing fixes. This leaves applications vulnerable to CVEs.

Recent history highlights the severity of this issue. Spring vulnerabilities affecting versions prior to 6.0 include CVEs allowing for Remote Code Execution via Java deserialization and unauthorized path traversal. In these scenarios, attackers could execute arbitrary code or navigate outside the intended web root directory. Here's a table showing CVEs in Spring Framework releases:

Without community support, the only way to remediate these vulnerabilities is to upgrade to the latest supported version or to secure Spring long-term support that provides backported patches.

Strategies for Regaining Control

Regaining control of the Java release cycle requires a proactive approach to dependency management. Organizations should implement a four-step strategy to stabilize their environments:

1. Audit: regularly identify all dependencies, including transitive ones. Tools like Maven's dependency:tree or Gradle's dependencies task can reveal vulnerable or outdated libraries hiding in the build.
2. Govern: Implement strict policies for version control. Do not allow unapproved dependencies into the build without vetting. Using an internal repository manager to proxy and scan public artifacts is a best practice for preventing bad code from entering the ecosystem.
3. Stabilize: Use dependency locking to ensure that new builds do not automatically pull in the latest versions of libraries, which could introduce unexpected breaking changes.
4. Migrate: Plan for incremental upgrades. Rather than attempting a "big bang" migration, regularly update supported frameworks to incorporate fixes and maintain compatibility with modern standards.

When migrating between major versions, it is critical to do performance testing. Performance degradation can happen even with very minimal changes to the code base. An existing issue with the application could be exposed only in production. Teams sometimes make the mistake of testing with very low load/traffic which is uncharacteristic to how their production environment behaves.

The Role of Long-Term Support (LTS)

For many organizations, the pace of community releases is simply too fast to match their internal development cycles. This is where Long-Term Support (LTS) becomes an essential component of the software lifecycle strategy.

LTS programs buoy EOL software, providing a longer runway for migration planning. Unlike standard development streams that focus on new features, LTS focuses exclusively on stability and security. This includes:

• Ongoing Security Patches: Critical fixes for CVEs.
• Backported Fixes: Resolving defects in older versions without forcing a major upgrade.
• Compatibility: Ensuring legacy applications can run securely on modern infrastructure.

OpenLogic offers Spring LTS, extending support for EOL versions of Spring Boot and Spring Framework that many teams are still relying on. This allows enterprises to separate the urgency of security patching from the complexity of architectural migration. Development teams can have the breathing room they need to plan a successful upgrade without being rushed due to an immediate security threat. Additionally, OpenLogic's Professional Services team can help organizations modernize their application build process. 

Final Thoughts

The web of Spring dependencies in legacy applications is complex, but it does not have to be a liability. By understanding the risks of transitive dependencies, the impact of the Jakarta namespace shift, and the necessity of aligning with JDK versions, IT leaders can make informed decisions about their application roadmaps.

Whether the goal is to decommission a legacy app or prepare it for a major upgrade, stability is the prerequisite for success. Utilizing LTS from an enterprise support vendor like OpenLogic ensures that the application remains secure and compliant, preserving business continuity while the path forward is defined.

Additional Resources

• Blog - Managing EOL Spring Vulnerabilities
• Blog - Planning Your Next Spring Boot Upgrade
• Blog - Monitoring Spring Boot Applications in a Microservices World