how to inject a property at maven build time that is accessible later at runtime in a java project?

Question

I'm trying to inject a property into a java project when it is built by maven, by injecting the property via the command line, like

mvn clean install -DMYPROP=myProperty

I thought this was enough to have maven transform this into a System property, which could then be accessed in java via System.getProperty("MYPROP"). But this hasn't worked.

So I did more research, one post here pointed to Maven Properties, so I tried the following, in the pom.xml:

<properties>
    <MY.VARIABLE>${MYPROP}</MY.VARIABLE>
    <MY.ENV.VARIABLE>${env.MYPROP}</MY.ENV.VARIABLE>
</properties>

This is not working either. All the following properties are null

System.getProperty("MYPROP")
System.getProperty("MY.VARIABLE")
System.getProperty("MY.ENV.VARIABLE")

I've also tried using a properties-maven-plugin, based on another question. That property was null as well.

Any suggestions?

What you are doing is installing a package into your local repository. To pass the property to your java application, you need to pass it during execution. — Michael, Dec 23 '19 at 20:50

Petr Aleksandrov · Answer 1 · 2020-01-02T14:41:18.217

You can save the properties to the file inside the build artifact.

E.g. file src/main/resources/myProperties.properties

mavenProperty=${MYPROP}

You need to tune filtering in pom.xml:

<project>
...
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

Then, when you run maven with -DMYPROP=some-value, myProperties.properties will contain:

mavenProperty=some-value

So you will be able to get some-value in runtime by loading the property resource (and not with System.getProperty(..)):

public class App {                                                             

  public static void main(String[] args) throws IOException {                  
    Properties properties = new Properties();                                  
    properties.load(App.class.getResourceAsStream("/myProperties.properties"));
    properties.get("mavenProperty");                                             
  }                                                                            

}

Thanks, but I'm confused by the `mavenProperty=${MYPROP}` which is originally in the properties file. According to this, it looks like it will be overridden by the filtering to be `MYPROP=myProperty`. So what is the point of having the originaly mavenProperty? Looks like that is never used. — user26270, Dec 30 '19 at 17:20
Thank you for the note. There was a confusion in the property name. It's fixed now. `mavenProperty` property is available in runtime. `${MYPROP}` in the file can be replaced to the value you pass to maven: `-DMYPROP=some-value`. — Petr Aleksandrov, Jan 02 '20 at 14:49

score 1 · Answer 2 · answered Dec 23 '19 at 20:48

I use Maven Resources Plugin to write the Maven properties into a .properties file.

In your POM, specify the directory that contains the properties file and enable filtering:

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

Then in a properties file, like: src/main/resources/application.properties, reference a property:

my.property=${my.maven.property}

Then, when you build the project your property will be written into the properties file in the target/ dir. Then in your application, at runtime load the properties file and access the value.

The destination is correctly `target/classes` directory and not `target`... — khmarbaise, Dec 23 '19 at 21:36

score 1 · Answer 3 · answered Dec 23 '19 at 21:32

There are several ways of achieving your goal. Below is one of them.

No matter what you decide to do, using a properties file to store your properties is a good practice.

With maven you can use profiles and create different properties files for different profiles. To make maven pass the property value to the property file, use resource filtering. Example below:

<project ... >
    .
    .
    .
    <profiles>
        <profile>
            <id>dev</id>
            <activation>
                <activeByDefault>true</activeByDefault>
            </activation>
            <properties>
                <my.prop>dev_value</my.prop>
            </properties>
        </profile>
        <profile>
            <id>prod</id>
            <properties>
                <my.prop>prod_value</my.prop>
            </properties>
        </profile>
    </profiles>
    .
    .
    .
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>

Inside the src/main/resources/my_properties.properties file, use:

my.prop=${my.prop:default_value}

This will eventually replace the value of my.prop and if none is found, the default value default_value will be used.

Hope this helps.

score 0 · Answer 4 · answered Dec 23 '19 at 20:44

0

As far as I know, there is no way to set a System property for the Java application that you build.

If you want to save information for later use inside the Java application, you can use properties files as resources that are packed into the jar.

answered Dec 23 '19 at 20:44

J Fabian Meier

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how to inject a property at maven build time that is accessible later at runtime in a java project?

4 Answers4