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tracing-agent.mdplugins/developer-kit-java/skills/graalvm-native-image/references/

GraalVM Tracing Agent

Guide for using the GraalVM tracing agent to automatically collect reachability metadata for native image builds.

Table of Contents

  1. Overview
  2. Running the Tracing Agent
  3. Agent Modes
  4. Integration with Build Tools
  5. Filtering and Fine-Tuning

Overview

The GraalVM tracing agent intercepts all dynamic accesses (reflection, resources, JNI, proxies, serialization) during application execution on the JVM and generates the corresponding GraalVM metadata files.

When to use the tracing agent:

  • Initial native image migration of a complex project
  • After adding new libraries with reflection requirements
  • When manual metadata configuration is insufficient
  • To discover hidden reflection/resource usage

Important: The agent only captures code paths exercised during the run. Ensure thorough coverage by running all application features, endpoints, and edge cases.

Running the Tracing Agent

Basic Usage

# Create output directory
mkdir -p src/main/resources/META-INF/native-image

# Run with the tracing agent
java -agentlib:native-image-agent=config-output-dir=src/main/resources/META-INF/native-image \
    -jar target/myapp.jar

Then exercise all application features (call APIs, trigger scheduled tasks, etc.) before shutting down gracefully.

With Spring Boot

# Run Spring Boot app with tracing agent
java -agentlib:native-image-agent=config-output-dir=src/main/resources/META-INF/native-image \
    -jar target/myapp.jar

# Exercise all endpoints
curl http://localhost:8080/api/users
curl -X POST http://localhost:8080/api/users -H 'Content-Type: application/json' -d '{"name":"test"}'
curl http://localhost:8080/actuator/health

# Shut down gracefully (Ctrl+C or kill -SIGTERM)

Merging with Existing Config

# Merge agent output with existing metadata (does not overwrite)
java -agentlib:native-image-agent=config-merge-dir=src/main/resources/META-INF/native-image \
    -jar target/myapp.jar

Agent Modes

Output Mode (Fresh Config)

Writes new configuration, overwriting any existing files:

-agentlib:native-image-agent=config-output-dir=<path>

Merge Mode (Append to Existing)

Merges new entries into existing configuration files:

-agentlib:native-image-agent=config-merge-dir=<path>

Conditional Mode

Generate conditional metadata (only include if a type is reachable):

-agentlib:native-image-agent=config-output-dir=<path>,experimental-conditional-config-filter-file=filter.json

Integration with Build Tools

Maven — Run Agent During Tests

<profiles>
  <profile>
    <id>agent</id>
    <build>
      <plugins>
        <plugin>
          <groupId>org.graalvm.buildtools</groupId>
          <artifactId>native-maven-plugin</artifactId>
          <configuration>
            <agent>
              <enabled>true</enabled>
              <options>
                <option>config-output-dir=src/main/resources/META-INF/native-image</option>
              </options>
            </agent>
          </configuration>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-surefire-plugin</artifactId>
          <configuration>
            <argLine>-agentlib:native-image-agent=config-output-dir=src/main/resources/META-INF/native-image</argLine>
          </configuration>
        </plugin>
      </plugins>
    </build>
  </profile>
</profiles>

Run with:

./mvnw -Pagent test

Gradle — Run Agent During Tests

graalvmNative {
    agent {
        defaultMode.set("standard")
        metadataCopy {
            inputTaskNames.add("test")
            outputDirectories.add("src/main/resources/META-INF/native-image")
            mergeWithExisting.set(true)
        }
    }
}

Run with:

# Run tests with agent
./gradlew -Pagent test

# Copy collected metadata
./gradlew metadataCopy

Filtering and Fine-Tuning

Agent Filter Configuration

Create a filter file to reduce noise in the generated metadata:

{
  "rules": [
    {
      "excludeClasses": "jdk.internal.**"
    },
    {
      "excludeClasses": "sun.**"
    },
    {
      "excludeClasses": "com.sun.**"
    },
    {
      "includeClasses": "com.example.**"
    }
  ]
}

Use with:

java -agentlib:native-image-agent=config-output-dir=<path>,caller-filter-file=filter.json \
    -jar target/myapp.jar

Post-Processing Agent Output

After collecting metadata, review and clean up:

  1. Remove unnecessary entries — The agent is conservative; many entries may not be needed
  2. Add conditions — Use condition.typeReached to limit when metadata is applied
  3. Verify correctness — Build the native image and test thoroughly
  4. Commit metadata — Add the generated files to version control

Recommended Workflow

# 1. Run agent with tests for baseline coverage
./mvnw -Pagent test

# 2. Run agent with the full application for runtime coverage
java -agentlib:native-image-agent=config-merge-dir=src/main/resources/META-INF/native-image \
    -jar target/myapp.jar
# Exercise all features, then shut down

# 3. Build native image
./mvnw -Pnative package

# 4. Test the native executable
./target/myapp

# 5. If failures occur, repeat steps 2-4 with additional code paths

plugins

developer-kit-java

skills

graalvm-native-image

references

gradle-native-plugin.md

maven-native-profile.md

quarkus-micronaut-native.md

reflection-resource-config.md

spring-boot-native.md

tracing-agent.md

SKILL.md

README.md

tile.json