JAR file not able to read application.properties in Maven Springboot project

Troubleshooting Spring Boot JAR File Not Reading application.properties in a Maven Project

When running a Spring Boot project via the IDE, everything seems fine, but the project fails after building and running the JAR file. If you encounter an error like:

Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'secure.url' in value "${secure.url}"

It indicates that the application cannot locate or resolve the placeholder secure.url defined in your application.properties or environment variables. This post will guide you on how to troubleshoot and resolve this issue.

Root Cause

This problem typically arises because:

1. Configuration properties (like application.properties or application.yml) are not included in the built JAR.
2. The path to the configuration file is incorrectly specified.
3. Placeholder values are missing from the properties file or are not provided as environment variables.

Steps to Resolve

1. Verify application.properties is Included in the JAR

By default, Maven should package application.properties (or application.yml) into the src/main/resources folder. Confirm that:

• The application.properties file exists in the correct location:

  src/main/resources/application.properties

• Check the target folder after running mvn clean install. Open the JAR file and ensure application.properties is located under BOOT-INF/classes/.

If it’s missing, add the following configuration to your pom.xml:

<build>
    <resources>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.yml</include>
            </includes>
        </resource>
    </resources>
</build>

2. Check Placeholder Configuration

Ensure the secure.url key is defined in application.properties or as an environment variable. For example:

secure.url=https://example.com

If this is dynamically configured through profiles, ensure the correct profile is being picked up. Add the --spring.profiles.active argument when running the JAR:

java -jar your-app.jar --spring.profiles.active=prod

3. Provide External application.properties (Optional)

If your application.properties is external, ensure it is referenced correctly. Place the file alongside the JAR and use:

java -jar your-app.jar --spring.config.location=file:./application.properties

4. Debug Classpath Issues

Run the following command to check the classpath at runtime:

java -cp your-app.jar org.springframework.boot.loader.JarLauncher

Ensure application.properties is being detected.

Common Pitfalls

1. Custom Properties Files: If you’re using a non-standard name for application.properties, configure it explicitly in your application.yml:

   spring:<br>     config:<br>       name: custom-application

2. Incorrect Packaging: Ensure the project uses the spring-boot-maven-plugin for proper packaging:

   <build>
       <plugins>
           <plugin>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-maven-plugin</artifactId>
           </plugin>
       </plugins>
   </build>

3. Environment Variables Overriding Defaults: Sometimes, environment variables can unintentionally override application.properties. Use --debug to identify mismatches.

Conclusion

By following the steps above, you should be able to resolve the Could not resolve placeholder error in your Spring Boot application. Ensure all required properties are included in the correct files and properly packaged with the JAR. If the issue persists, debug the classpath and profiles to locate missing configurations.

By addressing this, your application should run smoothly and meet your project timelines.

Let me know if you need help with specific parts of your configuration!