如何从Maven POM中的文件设置构建属性？

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?

Answer 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.

Answer 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.