GraalVM Native Image: Fixing Jjwt-orgjson Build Failures

Nov 16, 2025 by Alex Johnson 57 views

When working with Java applications, especially those that aim for performance and efficient deployment, using GraalVM's Native Image feature can be a game-changer. It allows you to compile your Java code ahead-of-time into a standalone executable, significantly reducing startup times and memory footprint. However, like any powerful tool, it comes with its own set of challenges. One such hurdle can arise when trying to build a native executable for a project that uses libraries like io.jsonwebtoken:jjwt-orgjson, specifically version 0.12.7, which we'll explore here after encountering a native-image run failure. This article will dive into the intricacies of this issue, offering insights and potential solutions to get your GraalVM native image builds back on track.

Understanding the GraalVM Native Image Build Process

Before we dive into the specifics of the io.jsonwebtoken:jjwt-orgjson:0.12.7 failure, it's crucial to understand what GraalVM Native Image does. When you invoke native-image, it performs a complex process involving several stages. First, it analyzes your application code to determine all the classes, methods, and fields that are reachable from the entry point. This is a static analysis, meaning it doesn't execute your code but rather traces potential execution paths. This analysis is vital because, unlike the standard Java Virtual Machine (JVM) which uses a Just-In-Time (JIT) compiler and loads classes dynamically, a native image needs to have all its required code included at build time. Any class, method, or field that could be used but isn't explicitly discovered during the analysis might be missing, leading to runtime errors. This is where graalvm-reachability-metadata comes into play, aiming to provide the necessary information for GraalVM to correctly analyze and include all required components for various libraries.

The build process itself involves several steps, as seen in the provided log: initialization, analysis, building the universe, parsing methods, inlining, compiling methods, laying out methods, and finally, creating the image. Each step has its own complexities and potential failure points. The analysis phase, in particular, is where most issues related to missing types or reflection configurations occur. The log shows a substantial number of reachable types, fields, and methods, along with entries for reflection, JNI access, and loaded native libraries. The detailed breakdown of code area origins and object types in the image heap gives us a glimpse into what parts of the Java runtime and third-party libraries are being included. Understanding these stages helps in diagnosing why a build might fail and where to look for clues. For instance, if a library relies heavily on reflection or dynamic class loading in ways that aren't immediately apparent from the static analysis, GraalVM might miss crucial components, leading to the very errors we are investigating.

Furthermore, GraalVM Native Image's goal is to produce a highly optimized executable. This optimization involves aggressive inlining, method compilation, and efficient memory layout. While this contributes to the impressive performance gains, it also means that the build process is sensitive to how the code is structured and how dependencies are managed. The log also points out recommendations, such as using G1 GC, PGO, and enabling more CPU features, which are geared towards further performance tuning post-build. However, our immediate concern is the build failure itself, which occurs before we even get to the stage of runtime performance optimization. The core of the problem lies in the static analysis and code inclusion phase, where certain components required by io.jsonwebtoken might not be correctly identified or configured for the native image environment.

Debugging the `io.jsonwebtoken:jjwt-orgjson:0.12.7` Native Image Failure

The core of the problem, as indicated by the build log and the stack traces, points to an ExceptionInInitializerError and NoClassDefFoundError originating from io.jsonwebtoken.Jwts$SIG and its dependency on io.jsonwebtoken.lang.UnknownClassException: Unable to load class named [io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier]. This error message is a critical clue. It suggests that when the Jwts.SIG static initializer was being processed during the native image build, it tried to load a class named io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier, but it couldn't find it. The error explicitly asks, "Have you remembered to include the jjwt-impl.jar in your runtime classpath?"

This question is particularly relevant in the context of GraalVM Native Image. Unlike a standard JVM execution where all JARs on the classpath are typically available, Native Image performs a deep analysis and includes only what it deems necessary. If jjwt-impl.jar contains classes that are dynamically loaded or accessed via reflection, and these accesses aren't explicitly configured or detected by the reachability analysis, those classes might be excluded from the final native image. The fact that the error mentions io.jsonwebtoken.lang.Classes.forName and io.jsonwebtoken.lang.Classes.newInstance further reinforces the idea that the library is using reflection or a similar dynamic mechanism to instantiate classes.

In this specific case, the failure occurs when trying to initialize io.jsonwebtoken.Jwts$SIG. This static block likely attempts to instantiate DefaultJwtBuilder$Supplier or use it in some way. The jjwt-orgjson artifact itself primarily provides JSON object support for JWTs, relying on other jjwt artifacts like jjwt-api and jjwt-impl for the core JWT functionalities. If the jjwt-impl artifact's necessary components aren't correctly registered or included in the native image configuration, any part of the jjwt library that depends on them will fail. The GVM_TCK_LV="0.12.7" ./gradlew clean test -Pcoordinates="io.jsonwebtoken:jjwt-orgjson:0.12.0" command suggests an attempt to test a specific version of jjwt-orgjson (0.12.0) using environment variables that might be related to 0.12.7, potentially introducing versioning complexities or misconfigurations.

To address this, we need to ensure that all classes used by io.jsonwebtoken, particularly those in jjwt-impl, are correctly recognized by GraalVM Native Image. This often involves providing explicit configuration to the native-image tool, typically through reachability metadata files. These files can guide the analysis to include specific classes, configurations for reflection, JNI, and resource loading. The provided log shows that configuration files from /home/runner/work/graalvm-reachability-metadata/graalvm-reachability-metadata/metadata/io.jsonwebtoken/jjwt-orgjson/0.12.0 are being used, which is good. However, it seems the metadata might be incomplete for this specific version or scenario. The failure occurring in static initializers (<clinit>) is a classic sign that essential classes or resources were missed during the analysis phase.

Strategies for Resolution

When faced with such a NoClassDefFoundError or ExceptionInInitializerError in a GraalVM Native Image build, especially related to dynamic class loading or reflection, several strategies can be employed. The primary goal is to provide GraalVM with the necessary information to include all required components in the final executable.

Adding Explicit Reachability Metadata: The most direct approach is to create or update the GraalVM reachability metadata for the io.jsonwebtoken library. This involves creating configuration files (.json or .properties) that tell native-image to include specific classes, register them for reflection, or load them as resources. For this particular issue with io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier, you would typically add an entry like this to a reflect-config.json file within the metadata:
```
[
  {
    "name": "io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier",
    "allDeclaredConstructors": true,
    "allDeclaredMethods": true
  }
]
```
You might also need to ensure that jjwt-impl.jar is correctly referenced in the build process so that its classes are available for analysis. The fact that jjwt-orgjson is being tested suggests that jjwt-api and jjwt-impl should also be dependencies available during the native image build. The org.graalvm.junit.platform.JUnitPlatformFeature is being used, which is correct for running JUnit tests within a native image, but it doesn't automatically solve the underlying dependency issues.
Using the native-image-agent: If you're unsure about what exactly is missing, you can run your application (or its relevant parts) under the standard JVM with the native-image-agent enabled. This agent monitors runtime behavior, including class loading, reflection, and JNI calls. After the application runs, it generates configuration files that can then be fed to the native-image tool. This is an empirical approach that can be very effective for uncovering dynamically accessed components. You would typically run your tests on the JVM with the agent active, collect the generated configuration, and then use those configurations during the native-image build.
Checking Version Compatibility: Ensure that the versions of jjwt-api, jjwt-impl, and jjwt-orgjson are compatible with each other and with the GraalVM version you are using. Sometimes, issues arise due to incompatibilities between library versions or between a library and a specific GraalVM release. The command used in the log, GVM_TCK_LV="0.12.7" ./gradlew clean test -Pcoordinates="io.jsonwebtoken:jjwt-orgjson:0.12.0", is a bit ambiguous with version numbers. It's important to be consistent and verify that all jjwt artifacts are at a version that has known good compatibility with GraalVM, or for which reachability metadata is available and maintained.
Examining Library Internals: As a last resort, or for deeper understanding, you can examine the source code of jjwt-impl and related classes (like Jwts and DefaultJwtBuilder) to understand how they dynamically load classes or use reflection. This can help pinpoint exactly what needs to be configured. The error message io.jsonwebtoken.lang.UnknownClassException: Unable to load class named [io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier] strongly suggests that DefaultJwtBuilder$Supplier is a class that needs to be explicitly configured for use with GraalVM. If this class is an inner class of DefaultJwtBuilder, it might require specific reflection configuration for the outer class or the inner class itself, depending on how it's accessed.

In the context of the provided log, the issue seems to be that the jjwt-impl library's internal mechanisms for loading components, possibly related to JWT builders or signature handling, are not being correctly discovered by GraalVM's static analysis. The graalvm-reachability-metadata project aims to provide these configurations. If the metadata for jjwt-orgjson version 0.12.0 (or 0.12.7 if that's the intended version) is missing or incomplete, this build failure is a likely outcome. The solution would involve adding the necessary reachability metadata, possibly in the form of reflection configuration, to ensure that classes like io.jsonwebtoken.impl.DefaultJwtBuilder$Supplier are available when needed.

The Path Forward: Ensuring Successful Native Image Builds

Successfully building native executables with GraalVM often involves a collaborative effort between library authors and the community to provide comprehensive reachability metadata. For libraries like io.jsonwebtoken, which are widely used for security-related tasks, ensuring compatibility with GraalVM Native Image is crucial for many applications. The graalvm-reachability-metadata project is a fantastic initiative that serves as a central repository for these configurations.

When you encounter a build failure like the one described, especially with a clear error message pointing to missing classes or reflection issues, the first step is often to check if updated or correct metadata already exists. If not, contributing this metadata is highly valuable. The process typically involves identifying the missing classes or configurations from the error messages and then creating or updating the corresponding .json files in the metadata repository. For io.jsonwebtoken:jjwt-orgjson, this means ensuring that the jjwt-impl module's dynamic aspects are properly handled.

It's also important to stay updated with GraalVM releases and the graalvm-reachability-metadata project. As both evolve, new features might be introduced, or existing metadata might be refined. For developers using these libraries, keeping dependencies current and testing against recent GraalVM versions can help catch issues early. The recommendations provided by the native-image tool itself, such as using --gc=G1 or enabling -march=native, are primarily for performance tuning after a successful build. The immediate concern is to overcome the build errors. Focusing on the analysis and configuration phases is key.

In summary, the failure when building a native image for io.jsonwebtoken:jjwt-orgjson is typically due to missing reachability metadata, preventing GraalVM from finding necessary classes that are dynamically loaded or accessed via reflection. By providing explicit configurations, using the native-image-agent, and ensuring version compatibility, you can overcome these challenges. The ongoing work on graalvm-reachability-metadata is essential for the broader adoption of Java applications with GraalVM Native Image.

For further assistance and more in-depth information on GraalVM Native Image, you can refer to the official GraalVM Documentation or explore the GraalVM Community Forum. These resources offer extensive guides, troubleshooting tips, and a platform to connect with other users and experts.