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         


        

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

    4.0.0

    com.stackoverflow
    Q12082277
    1.0-SNAPSHOT
    pom

    ${project.artifactId}-${project.version}

    
        plugin
        app
    

plugin/pom.xml

    4.0.0

    
        com.stackoverflow
        Q12082277
        1.0-SNAPSHOT
    

    Q12082277-plugin
    maven-plugin

    ${project.artifactId}-${project.version}

    
        
            org.apache.maven
            maven-plugin-api
            3.0.4
        
        
            org.apache.maven
            maven-project
            2.2.1
        
    

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

    4.0.0

    
        com.stackoverflow
        Q12082277
        1.0-SNAPSHOT
    

    Q12082277-app

    ${project.artifactId}-${project.version}

    
        
            
                com.stackoverflow
                Q12082277-plugin
                1.0-SNAPSHOT
                
                    
                        initialize
                        
                            extract
                        
                        
                            ${user.home}/my.properties
                        
                    
                
            
            
                org.codehaus.mojo
                exec-maven-plugin
                1.2.1
                
                    
                        
                            java
                        
                    
                
                
                    com.stackoverflow.Q12082277.App
                
            
        
        
            
                src/main/resources
                true
            
        
    

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.