Add Build Properties to a Spring Boot Application

1. Introduction

Usually, our project's build configuration contains quite a lot of information about our application. Some of this information might be needed in the application itself. So, rather than hard-code this information, we can use it from the existing build configuration.

In this article, we'll see how to use information from the project's build configuration in a Spring Boot application.

2. The Build Information

Let's say we want to display the application description and version on our website's home page.

Usually, this information is present in pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <artifactId>spring-boot</artifactId>
    <name>spring-boot</name>
    <packaging>war</packaging>
    <description>This is simple boot application for Spring boot actuator test</description>
    <version>0.0.1-SNAPSHOT</version>
...
</project>

3. Referencing the Information in the Application Properties File

Now, to use the above information in our application, we'll have to first reference it in one of our application properties files:

application-description=@project.description@
application-version=@project.version@

Here, we've used the value of the build property project.description to set the application property application-description. Similarly, application-version is set using project.version.

The most significant bit here is the use of the @ character around the property name. This tells Spring to expand the named property from the Maven project.

Now, when we build our project, these properties will be replaced with their values from pom.xml.

This expansion is also referred to as resource filtering. It's worth noting that this kind of filtering is only applied to the production configuration. Consequently, we cannot use the build properties in the files under src/test/resources.

Another thing to note is that if we use the addResources flag, the spring-boot:run goal adds src/main/resources directly to the classpath. Although this is useful for hot reloading purposes, it circumvents resource filtering and, consequently, this feature, too.

Now, the above property expansion works out-of-the-box only if we use spring-boot-starter-parent.

3.1. Expanding Properties Without spring-boot-starter-parent

Let's see how we can enable this feature without using the spring-boot-starter-parent dependency.

First, we have to enable resource filtering inside the <build/> element in our pom.xml:

<resources>
    <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
    </resource>
</resources>

Here, we've enabled resource filtering under src/main/resources only.

Then, we can add the delimiter configuration for the maven-resources-plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-resources-plugin</artifactId>
    <configuration>
        <delimiters>
            <delimiter>@</delimiter>
        </delimiters>
        <useDefaultDelimiters>false</useDefaultDelimiters>
    </configuration>
</plugin>

Note that we've specified the useDefaultDelimiters property as false. This ensures that the standard Spring placeholders such as ${placeholder} are not expanded by the build.

4. Using the Build Information in YAML Files

If we're using YAML to store application properties, we might not be able to use @ to specify the build properties. This is because @ is a reserved character in YAML.

But, we can overcome this by either configuring a different delimiter in maven-resources-plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-resources-plugin</artifactId>
    <configuration>
        <delimiters>
            <delimiter>^</delimiter>
        </delimiters>
        <useDefaultDelimiters>false</useDefaultDelimiters>
    </configuration>
</plugin>

Or, simply by overriding the resource.delimiter property in the properties block of our pom.xml:

<properties>
    <resource.delimiter>^</resource.delimiter>
</properties>

Then, we can use ^ in our YAML file:

application-description: ^project.description^
application-version: ^project.version^

5. Conclusion

In this article, we saw how we could use Maven project information in our application. This can help us to avoid hardcoding the information that's already present in the project build configuration in our application properties files.

And of course, the code that accompanies this tutorial can be found over on GitHub.