Resolving Build Method Not Found Errors With Lombok Jackson And GraalVM

Hey guys! Have you ever encountered that frustrating build method not found error when working with Lombok, Jackson, and GraalVM in your Micronaut projects? It's a tricky issue, but fear not! We're going to dive deep into the root cause and explore how to resolve it. This article is all about understanding the interaction between these technologies and ensuring your applications run smoothly, especially when using native image compilation with GraalVM.

Understanding the Problem

Let's start by understanding the scenario. Imagine you're using Lombok to generate builders for your data classes, Jackson for JSON serialization and deserialization, and GraalVM to compile your Micronaut application into a native image. Everything seems fine during development, but when you run the native image, you encounter a build method not found error. What's going on?

The error typically arises when Jackson tries to use the builder generated by Lombok to deserialize JSON into your objects. Jackson relies on the presence of a build method to finalize the object creation process. However, GraalVM's static analysis might not detect the usage of this build method during the image build process, leading to its removal from the native image. This is where the build method not found error pops up.

The key players in this issue are:

• Lombok: Generates boilerplate code, including builders, reducing the amount of manual code you need to write.
• Jackson: A powerful Java library for serializing and deserializing JSON.
• GraalVM: A high-performance virtual machine that can compile Java applications into native images, offering faster startup times and reduced memory footprint.
• Micronaut: A full-stack, JVM-based framework for building modular, easily testable microservice and serverless applications.

The interaction between these technologies, especially with Micronaut's module-scan feature and BeanIntrospectionModule, adds another layer of complexity. Understanding how these components work together is crucial to pinpointing the cause of the error.

Diving Deep into the Code

To really get to grips with the problem, let's delve into the code execution flow. The issue often surfaces when using Micronaut's module-scan feature, which automatically installs the BeanIntrospectionModule. This module optimizes Jackson's serialization and deserialization process by using Bean Introspection instead of traditional reflection. But how does this lead to the build method issue?

Here's a breakdown of the code flow:

1. Jackson's Builder Detection: Jackson recognizes the existence of a builder class due to annotations (e.g., @JsonPOJOBuilder). It also identifies properties based on @JsonProperty annotations.
2. Property List Creation: Jackson creates a preliminary list of properties based on the @JsonProperty annotations.
3. Empty Builder Instance: Jackson instantiates an empty builder object.
4. Bean Introspection Module Enrichment: This is where things get interesting. Instead of using its own reflection mechanisms, Jackson delegates the task of enriching the builder to the BeanIntrospectionModule.
5. Introspection-Based Setter Discovery: The BeanIntrospectionModule leverages introspection to discover relevant setter methods within the builder. It then populates the builder instance with the values from the JSON data.
6. Enriched Builder Return: The BeanIntrospectionModule returns the enriched builder instance back to Jackson.
7. Final Builder Setup: Jackson attempts to complete the builder setup, which includes invoking the build method to create the final object.

Now, the crucial part: GraalVM's static analysis comes into play. It identifies properties used by the IntrospectionModule and includes them in the native image. However, it might miss the build method itself because it doesn't appear to be directly used during the analysis. This is a classic case of static analysis limitations.

The Missing build Method

Before handing the builder over to the BeanIntrospectionModule, Jackson tries to locate the build method using reflection. This is a critical step, but it's also where the problem surfaces. If GraalVM hasn't included the build method in the native image (because it wasn't deemed reachable during static analysis), this reflection attempt will fail. This is a core part of understanding why the build method not found error occurs.

When Jackson eventually checks for the presence of the _buildMethod (the cached reflection result for the build method), it finds nothing. This triggers the exception, as Jackson cannot finalize the object construction without the build method. The links in the original post to the Jackson code (find and here) highlight these critical points in the Jackson deserialization process.

Solutions and Workarounds

So, we've identified the problem: GraalVM's static analysis might exclude the build method, leading to Jackson's failure to complete object construction. What can we do about it? There are several approaches to tackle this issue, ranging from GraalVM configuration to code adjustments.

1. GraalVM Reachability Configuration

The most direct solution is to explicitly tell GraalVM to include the build method in the native image. This can be achieved through reachability metadata, which provides hints to GraalVM's static analysis. You can create a reflect.json configuration file that specifies the classes and methods that should be included in the native image. This is a powerful technique to ensure GraalVM retains the necessary components, but it does require some manual configuration.

Here's an example of what a reflect.json entry might look like:

[
 {
 "name": "your.package.YourBuilderClass",
 "methods": [
 {
 "name": "build",
 "parameterTypes": []
 }
 ]
 }
]

In this example, you would replace your.package.YourBuilderClass with the actual fully qualified name of your builder class. This configuration explicitly tells GraalVM to include the build method of this class in the native image, resolving the build method not found error.

2. @RegisterForReflection Annotation

Micronaut provides the @RegisterForReflection annotation, which offers a more convenient way to register classes and methods for reflection with GraalVM. By annotating your builder class or the build method itself, you can instruct Micronaut to generate the necessary reachability metadata during the native image build. This annotation simplifies the process of ensuring GraalVM includes the necessary reflection information, making it a more streamlined approach than manual configuration.

Here's how you might use @RegisterForReflection:

import io.micronaut.core.annotation.RegisterForReflection;

@RegisterForReflection
public class YourBuilderClass {
 // ... your builder class code ...
 public YourObjectClass build() {
 // ... build method logic ...
 }
}

Or, you can apply it directly to the build method:

import io.micronaut.core.annotation.RegisterForReflection;

public class YourBuilderClass {
 // ... other methods ...
 @RegisterForReflection
 public YourObjectClass build() {
 // ... build method logic ...
 }
}

Using @RegisterForReflection ensures that the build method is available at runtime, effectively preventing the build method not found error.

3. Disabling Bean Introspection

As we discussed earlier, the BeanIntrospectionModule plays a key role in this issue. While it optimizes Jackson's performance, it also introduces the potential for GraalVM to miss the build method during static analysis. If you're willing to trade some performance for simplicity, you can disable the BeanIntrospectionModule. This will force Jackson to use its default reflection mechanisms, which are more likely to be detected by GraalVM. However, keep in mind that disabling this module might impact the startup time and overall performance of your application.

To disable the BeanIntrospectionModule, you can exclude it from your dependencies or configure Jackson to not use it. The exact steps will depend on your project setup and build configuration. This is a viable workaround, but it's essential to weigh the performance implications against the simplicity it offers.

4. Explicitly Using the build Method

Another approach is to ensure that the build method is explicitly used somewhere in your code that GraalVM can analyze. This might involve adding a dummy usage of the build method or refactoring your code to make the usage more apparent. This method ensures that GraalVM's static analysis recognizes the build method as reachable and includes it in the native image. It's a clever way to trick GraalVM into including the necessary method, but it can also make your code less readable if not done carefully.

For example, you could add a test case that explicitly calls the build method, ensuring that it's included in the native image. This approach is particularly effective if you have comprehensive test coverage, as it naturally includes the necessary method calls.

5. Upgrade Jackson and Micronaut Versions

Sometimes, the issue might be due to a bug in a specific version of Jackson or Micronaut. Upgrading to the latest versions can often resolve the problem, as newer versions may include fixes or improvements that address the interaction with GraalVM. Always check the release notes for any relevant bug fixes or changes that might impact your application. This is a general best practice for maintaining a healthy and stable application.

Before upgrading, make sure to test your application thoroughly to ensure that the new versions don't introduce any compatibility issues or regressions. A well-tested upgrade is a safe upgrade.

Conclusion

The build method not found error when using Lombok, Jackson, and GraalVM can be a challenging issue to diagnose. However, by understanding the interaction between these technologies and the limitations of GraalVM's static analysis, you can effectively troubleshoot and resolve the problem. Whether you choose to use GraalVM reachability configuration, the @RegisterForReflection annotation, disable Bean Introspection, explicitly use the build method, or upgrade your dependencies, there are several paths to success. The key is to choose the solution that best fits your project's needs and constraints.

Remember, the goal is to create efficient and reliable applications. By addressing this issue head-on, you're ensuring that your Micronaut applications can leverage the power of native images without sacrificing functionality. So, go forth and build amazing things, guys!

Repair Input Keyword

• How to resolve the build method not found error when using Lombok, Jackson, and GraalVM in Micronaut applications? What are the possible causes and solutions?

Title

Resolving build Method Not Found Errors with Lombok, Jackson, and GraalVM