Getting Versions Aligned: Java, Gradle, Spring Boot, and Spring Cloud

Using Spring Boot and Spring Cloud can significantly speed up Java development, particularly for microservices. However, managing the dependencies between your JDK, build tool (like Gradle or Maven), Spring Boot, and Spring Cloud requires attention to detail. Version mismatches are a common source of problems, leading to build failures or runtime errors that can be difficult to diagnose.

This post outlines the compatibility requirements you need to be aware of, explains common errors caused by mismatches, provides methods for resolving them, and includes specific compatibility information for Gradle, Java, Spring Boot, and Spring Cloud.

Table Shortcuts

• Gradle and Java Compatibility
• Java Version Compatibility with Spring Boot
• Spring Cloud Compatibility with Spring Boot

Why Version Compatibility is Necessary

Spring Boot simplifies dependency management through its starters and managed dependencies (BOM). Spring Cloud builds on this, adding its own layer of managed dependencies. These systems work reliably when the versions are aligned because:

• APIs Change: Libraries evolve. Methods get added, removed, or change signatures. Code compiled against one version may fail at runtime if a different, incompatible version is present.
• Bytecode Requirements: Newer Java versions introduce bytecode features older JVMs can’t handle. Conversely, older libraries might rely on APIs removed in newer JDKs. Your build tool (Gradle/Maven) also has minimum JDK requirements.
• Transitive Dependencies: The dependencies managed by Spring Boot and Spring Cloud have their own dependencies. A mismatch anywhere in this chain can cause conflicts.

Gradle and Java

Before even considering Spring Boot, your build tool itself needs a compatible JDK to run. Gradle, like any Java application, has minimum and recommended Java versions. Furthermore, Gradle supports compiling and testing code using different Java versions than the one it runs on, configured via Java toolchains.

• Running Gradle: You need a compatible JDK installed and typically configured via JAVA_HOME or the Gradle daemon settings.

• Building Code: You configure sourceCompatibility and targetCompatibility in your build.gradle file, and ideally use Gradle’s Java toolchain support to ensure Gradle downloads and uses the specified JDK version for compilation and testing, regardless of the JDK it’s running on.

Common Errors from Version Mismatches

When versions aren’t correctly aligned between Java, your build tool, Spring Boot, and potentially Spring Cloud, you might encounter errors like:

• java.lang.ClassNotFoundException: The JVM can’t find a specific class file at runtime. This often points to a missing dependency or an incorrect version being loaded.

• java.lang.NoSuchMethodError: Code calls a method that existed at compile time, but is missing in the version of the library loaded at runtime. A classic sign of a version conflict.

• java.lang.AbstractMethodError: An attempt was made to call an abstract method, which can happen if library APIs changed between versions in incompatible ways.

• Compilation Failures: Often related to using Java language features not supported by the configured targetCompatibility bytecode level, or when Spring Boot/Cloud versions require APIs from a newer JDK than you’re using.

• Build Tool Errors: Gradle or Maven might fail if they are run with an incompatible JDK version (e.g., running Gradle 6 with JDK 17 might cause issues).

• Spring Framework Issues: Problems like UnsatisfiedDependencyException or BeanCreationException during application startup can sometimes stem from underlying library incompatibilities caused by version mismatches.

Resolving Compatibility Issues

Troubleshooting version conflicts involves a systematic approach:

• Consult Official Documentation: This is the primary source of truth. Check the specific version requirements for Gradle, Spring Boot, and Spring Cloud.

• Use Spring Initializr: For new projects, start.spring.io pre-selects compatible versions, providing a solid starting point.

• Utilize Maven/Gradle BOMs: Import the spring-boot-dependencies Bill of Materials (BOM) and, if used, the spring-cloud-dependencies BOM for your specific release train. This helps ensure consistent versions for transitive dependencies. It’s generally recommended to let these BOMs manage versions unless you have a specific reason to override one.

Maven Example (pom.xml)

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>${spring-boot.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

Gradle Example (build.gradle - using dependencyManagement plugin)

dependencyManagement {
    imports {
        // Import the BOMs
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}" // Specify Cloud version
        mavenBom "org.springframework.boot:spring-boot-dependencies:${springBootVersion}" // Specify Boot version
    }
}

• Inspect the Dependency Tree: Use mvn dependency:tree or gradle dependencies (or gradle buildEnvironment) to see the resolved dependency versions. Identify conflicts where different versions of the same library are being requested. Use exclusions or explicitly declare needed versions if necessary.

• Verify Build Tool Configuration: Ensure your Gradle or Maven setup is compatible with the JDK you’re using to run the build. For Gradle, explicitly configure Java toolchains for compiling and testing.

• Test Consistently: Implement unit and integration tests to catch runtime errors early.

Compatibility Reference Tables

Gradle and Java Compatibility

Key Points:

• Newer Gradle versions are generally required to support newer Java versions for running Gradle itself.
• While you might run Gradle 8 on JDK 17, you can still configure it to compile your project code for Java 8 or Java 11 using toolchains.
• Always check the specific Gradle version’s documentation, as support details can change between minor releases.

(https://docs.gradle.org/current/userguide/compatibility.html)

Java Version Compatibility with Spring Boot

Key Notes:

• Spring Boot 3.x requires Java 17 as a baseline.
• Spring Boot 2.x supports Java 8 but is tested with newer JDKs up to specific versions.

Reference doc (https://endoflife.date/spring-boot#java-compatibility)

Spring Cloud Compatibility with Spring Boot

Spring Cloud uses “Release Trains” (e.g., 2023.0.x). Each train corresponds to specific Spring Boot versions. Mixing versions not intended to work together is highly likely to cause issues.

Do not arbitrarily combine Spring Cloud trains and Spring Boot versions. Always check the documentation page for the specific Spring Cloud release train (e.g., 2023.0.1) to find its required Spring Boot version.

Final Thoughts

Managing version compatibility in the Java and Spring ecosystem is a necessary part of development. While tools like Spring Boot and Gradle significantly help, understanding the requirements and relationships between the JDK, build tool, Spring Boot, and Spring Cloud is key to avoiding common problems.

Prioritize checking official documentation, utilize BOMs for dependency management, inspect your build environment when issues arise, and maintain robust testing practices. This diligence helps ensure a smoother development process.

Disclaimer: Version compatibility information changes. Always refer to the official documentation for Gradle, Spring Boot, and Spring Cloud for the most accurate and up-to-date details pertinent to your project.