Resolving the Spring Boot Parameter Name Reflection Error

Problem Statement

When upgrading to Spring Boot 3.2.4 or later, you may encounter this error:

Name for argument of type [java.lang.String] not specified, and parameter name information not available via reflection. Ensure that the compiler uses the '-parameters' flag

This occurs when Spring MVC attempts to bind URL path parameters to method arguments using reflection. Here's a common scenario that triggers the error:

@PutMapping("/{uid}/test/{state}")
public void update(
        @PathVariable String uid,
        @PathVariable String state
) {
    // Method implementation
}

Spring needs either:

1. Explicit parameter names declared in annotations OR
2. Access to parameter names via reflection through the -parameters compiler flag

Without either of these, Spring can't determine how to map path variables to method parameters.

Effective Solutions

Solution 1: Configure Compiler Parameters

Most reliable approach: Ensure Java retains parameter names at compile time.

For Maven Projects (pom.xml)

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <parameters>true</parameters>
            </configuration>
        </plugin>
    </plugins>
</build>

For Gradle Projects (build.gradle)

tasks.withType(JavaCompile) {
    options.compilerArgs += '-parameters'
}

IDE-Specific Configuration

• VS Code:
  Enable Java > Compiler > Store information about method parameters in settings

• IntelliJ IDEA:
  Go to Build, Execution, Deployment > Compiler > Java Compiler
  Add -parameters to Additional command line parameters

<info> **Why this works:** The `-parameters` flag preserves method parameter names in bytecode, enabling Spring to access them via reflection. This solution avoids cluttering your code with redundant annotation parameters. </info>

Solution 2: Explicit Parameter Naming

Annotation-based solution: Manually specify parameter names.

Modify your method parameters to include explicit names:

@PutMapping("/{uid}/test/{state}")
public void update(
        @PathVariable("uid") String uid, 
        @PathVariable("state") String state
) {
    // Method implementation
}

Apply consistently across:

• @PathVariable
• @RequestParam
• @RequestHeader
• Other parameter-binding annotations

<tip> **When to use this approach:** - When you can't change build configuration - When parameter names in URL and method should differ - For codebases with inconsistent compiler settings </tip>

Troubleshooting Considerations

1. Command Line vs IDE Execution:
   The error often occurs when running via IDE without compiler flags configured:

   # Use build tool execution instead of IDE run
   ./mvnw spring-boot:run   # Maven
   ./gradlew bootRun         # Gradle

2. Verification Check:
   Confirm parameter retention using reflection:

   Method method = YourController.class.getMethod("update", String.class, String.class);
   Parameter[] parameters = method.getParameters();
   System.out.println(parameters[0].getName()); // Should return "uid"

3. Spring Framework Changes:
   Since Spring Framework 6, parameter name retention is stricter where previously debug information was sufficient.

Best Practices Recommendation

For maintainable solutions:

1. First choice: Configure -parameters in your build tool
   (Ensures consistent behavior across environments)

2. Secondary option: Explicit parameter naming
   (Works when build configuration can't be changed)

<warning> **Avoid mixing approaches** in the same project to prevent confusion. Consistent strategy across the codebase simplifies maintenance. </warning>

Both solutions resolve the reflection error while adhering to Spring Boot 3.x+ requirements. The compiler parameter approach provides cleaner code, while explicit naming offers more control over parameter binding names.