How to set build properties from a file in Maven POM?

Question

I need to read and filter a properties file from a location outside my project, say ${user.home}/my.properties. This properties file looks like this:

res.dir=/my/stuff/here
resource.dir=C:/${res.dir}
bin.dir=${resource.dir}/bin
cfg.dir=${resource.dir}/config

I have to do this in both my build and in my application when it runs. This is easy to do in Ant, using the PROPERTY tag. However, there doesn't seem to be a good way to do it in Maven.

So far I have tried the Maven <property> tag, the Maven <filter> tag and various permutations of other tags. Either my build fails or the unit tests fail, or both.

If I hardcode these properties into the POM, everything works, so I know the problem is just reading the properties.

I looked at the properties-maven-plugin but the plugin no longer seems to be maintained.

Is there a way to do this?

Solution 1

You could simply implement your own maven-plugin that will take care of this for you.

Here is an example with the following structure:

.
 |-- pom.xml
 |-- plugin
 |   `-- pom.xml
 |   `-- src
 |       `-- main
 |           `-- java
 `-- app
     `-- pom.xml
     `-- src
         `-- main
             `-- java

You will need to create a Mojo that takes the properties file as an input and then propagates the properties to the pom.xml of the app. The pom.xml will actually not be updated but just the project data in it.

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>

    <groupId>com.stackoverflow</groupId>
    <artifactId>Q12082277</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>${project.artifactId}-${project.version}</name>

    <modules>
        <module>plugin</module>
        <module>app</module>
    </modules>

</project>

plugin/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>

    <parent>
        <groupId>com.stackoverflow</groupId>
        <artifactId>Q12082277</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <artifactId>Q12082277-plugin</artifactId>
    <packaging>maven-plugin</packaging>

    <name>${project.artifactId}-${project.version}</name>

    <dependencies>
        <dependency>
            <groupId>org.apache.maven</groupId>
            <artifactId>maven-plugin-api</artifactId>
            <version>3.0.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.maven</groupId>
            <artifactId>maven-project</artifactId>
            <version>2.2.1</version>
        </dependency>
    </dependencies>
</project>

plugin/src/main/java/com/stackoverflow/Q12082277/plugin/PropertiesMojo.java

package com.stackoverflow.Q12082277.plugin;

import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugin.MojoFailureException;
import org.apache.maven.plugin.logging.Log;
import org.apache.maven.project.MavenProject;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;

/**
 * @author maba, 2012-08-24
 *
 * @goal extract
 */
public class PropertiesMojo extends AbstractMojo {

    private Log log;

    /**
     * The current project representation.
     * @parameter expression="${project}"
     * @required
     * @readonly
     */
    private MavenProject project;

    /**
     * A properties file
     *
     * @parameter expression="${propertiesFile}"
     * @required
     */
    private File propertiesFile;

    @Override
    public void execute() throws MojoExecutionException, MojoFailureException {
        log.info("Executing PropertiesMojo on " + propertiesFile.getAbsolutePath());

        try {
            Properties fileProperties = new Properties();
            fileProperties.load(new FileInputStream(propertiesFile));
            Properties projectProperties = project.getProperties();
            for (Object key : fileProperties.keySet()) {
                projectProperties.setProperty((String)key, (String) fileProperties.get(key));
            }
            project.getProperties().list(System.out);
        } catch (FileNotFoundException e) {
            throw new MojoFailureException("The file " + propertiesFile.getAbsolutePath() + " was not found!", e);
        } catch (IOException e) {
            log.error("");
        }

    }

    @Override
    public void setLog(Log log) {
        this.log = log;
    }
}

You will use this plugin from the following app/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>

    <parent>
        <groupId>com.stackoverflow</groupId>
        <artifactId>Q12082277</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <artifactId>Q12082277-app</artifactId>

    <name>${project.artifactId}-${project.version}</name>

    <build>
        <plugins>
            <plugin>
                <groupId>com.stackoverflow</groupId>
                <artifactId>Q12082277-plugin</artifactId>
                <version>1.0-SNAPSHOT</version>
                <executions>
                    <execution>
                        <phase>initialize</phase>
                        <goals>
                            <goal>extract</goal>
                        </goals>
                        <configuration>
                            <propertiesFile>${user.home}/my.properties</propertiesFile>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.2.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>java</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <mainClass>com.stackoverflow.Q12082277.App</mainClass>
                </configuration>
            </plugin>
        </plugins>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

And then you will have to add the following app.properties that will work as a template and take the values that we have just read from file and set them and create a concrete file app.properties that will be reachable from within the jar.

app/src/main/resources/app.properties

res.dir=${res.dir}
resource.dir=${resource.dir}
bin.dir=${bin.dir}
cfg.dir=${cfg.dir}

And finally here is a test application that just loads the app.properties from the classpath and prints the result.

app/src/main/java/com/stackoverflow/Q12082277/App.java

package com.stackoverflow.Q12082277;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * @author maba, 2012-08-23
 */
public class App {

    public static void main(String[] args) throws IOException {
        ClassLoader loader = App.class.getClassLoader();
        InputStream in = loader.getResourceAsStream("app.properties");
        Properties properties = new Properties();
        properties.load(in);
        properties.list(System.out);
    }
}

Now you can stand in the top directory and execute

mvn install

Then go down into the app folder and execute

mvn exec:java

And it will print

-- listing properties --
resource.dir=C://my/stuff/here
cfg.dir=C://my/stuff/here/config
bin.dir=C://my/stuff/here/bin
res.dir=/my/stuff/here

Which is exactly what you wanted.

Solution 2

I think it would be better if you turned the properties file into a template file and take the properties from the pom.xml using maven resource filtering.

A simple setup might look like this

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>

    <groupId>com.stackoverflow</groupId>
    <artifactId>Q12082277</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>${project.artifactId}-${project.version}</name>

    <properties>
        <res.dir>/default/stuff/here</res.dir>
        <resource.dir>${res.dir}</resource.dir>
        <bin.dir>${resource.dir}/bin</bin.dir>
        <cfg.dir>${resource.dir}/config</cfg.dir>
    </properties>

    <dependencies>
    <!-- Your dependencies -->
    </dependencies>

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

</project>

src/main/resources/app.properties

res.dir=${res.dir}
resource.dir=${resource.dir}
bin.dir=${bin.dir}
cfg.dir=${cfg.dir}

src/main/java/com/stackoverflow/Q12082277/App.java

package com.stackoverflow.Q12082277;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * @author maba, 2012-08-23
 */
public class App {

    public static void main(String[] args) throws IOException {
        ClassLoader loader = App.class.getClassLoader();
        InputStream in = loader.getResourceAsStream("app.properties");
        Properties properties = new Properties();
        properties.load(in);
        properties.list(System.out);
    }
}

System.out

-- listing properties --
resource.dir=/default/stuff/here
cfg.dir=/default/stuff/here/config
bin.dir=/default/stuff/here/bin
res.dir=/default/stuff/here

The pom.xml will have the default properties that are used by everybody.

If you want to override the values then call maven with input parameters:

mvn install -Dres.dir=/my/stuff/here -Dresource.dir="C:/${res.dir}"

System.out

-- listing properties --
resource.dir=C://my/stuff/here
cfg.dir=C://my/stuff/here/config
bin.dir=C://my/stuff/here/bin
res.dir=/my/stuff/here

By doing it this way everybody will have the same view of the properties and you can override them if you want to when running on your own machine.

Comments

[khmarbaise]

What brings you to the assumption that the plugin will not be maintained anymore ? Furthermore properties outside the Maven project will make your project depend on those things which will break the Maven concept to have all needed things for a Maven project inside the project itself. The question is why you are needing this?

[user1071914]

"The question is why you are needing this?" It's the corporate standard. It evolved in the days of Ant. I am no more happy with it than the rest of the Maven community seems to be. As for the plugin, even Codehaus lists it as "pre-release."

[user1071914]

Thanks for the suggestion, unfortunately the way it is currently laid out (with the properties in a separate file) is a corporate standard and is not up for discussion, so I'm stuck using it the way it is.

[maba]

@user1071914 Try to use the maven antrun plugin. It might do what you need.

[maba]

@user1071914 I added another answer that implements a simple mojo that does what you want.

[user1071914]

This appears to be the best answer - I'm not happy that this gaping hole in Maven's toolset hasn't been addressed, but hey, welcome to open source, I guess. :-(