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title Java Builds

The Java buildpack detects if your build is Java by looking for a pom.xml file. If found, Maven will download all dependencies and build the project.

Setting up your POM.XML file

If your app has any dependencies, the pom.xml file should include the maven-dependency-plugin.

It tells Maven to copy the jar files that your app depends on to the target/dependency directory.

Because we use Cloudnative Buildpacks, the pom.xml file needs to have a compatible structure to produce a correct build slug for Java.

<?xml version="1.0" encoding="UTF-8"?>
<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <version>1.0-SNAPSHOT</version>
    <artifactId>helloworld</artifactId>
    <dependencies>
        ...
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>3.0.1</version>
                <executions>
                    <execution>
                        <id>copy-dependencies</id>
                        <phase>package</phase>
                        <goals><goal>copy-dependencies</goal></goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Specify Java version

You can specify a Java version by adding a file called system.properties to your application.

Then set a java.runtime.version in the file:

java.runtime.version=13

Sample Java Procfile

Keep in mind, you must specify a PORT variable for the web process to expose the server to the internet.

web: java $JAVA_OPTS -cp target/classes:target/dependency/* com.example.MyJavaApplication