Maven: How to execute a dependency in a forked JVM? - maven

Question

Using maven-exec-plugin and a java goal I execute a jar program that validates some files in my project. When the validation fails, it calls System.exit to return a non zero return code.
The problem is that it executes in the same JVM as Maven, so when it calls exit, the processing stops since it does not fork.
I configured it to execute with maven-exec-plugin and a java goal (like in here ). The execute jar is in my Nexus repository, so I want to download it as a dependency in my pom.xml.
A very nice feature of configuring the maven-exec-plugin dependency is that it downloads the jar and all its dependencies, so it isn't necessary to use maven assembly plugin to include all jars in the executable.
How do I configure my pom.xml to execute a jar dependency and correctly stop when it fails?

Answer 1

I solved my problem. Basically, instead of using the java goal, I must use the exec goal, and run the java executable. The code below sets the classpath and the class with the main method.
This solution using the pom.xml and a Nexus repository has a lot of advantages over just handling a jar file for my users:
No need to install anything in the machine that will run it, be it a developer machine or a continuous integration one.
The validation tool developer can release new versions and it will be automatically updated.
The developer can turn it off with a simple parameter.
Also solves the original problem: the validation tool will execute in a separate process, so the maven process won't abort when it calls System.exit.
Here is a commented 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.company</groupId>
<artifactId>yourId</artifactId>
<version>1.0</version>
<properties>
<!--
Skip the validation executing maven setting the parameter below
mvn integration-test -Dvalidation.skip
-->
<validation.skip>false</validation.skip>
<java.version>1.8</java.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.6.0</version>
<executions>
<execution>
<id>MyValidator</id>
<phase>integration-test</phase> <!-- you can associate to any maven phase -->
<goals>
<goal>exec</goal> <!-- forces execution in another process -->
</goals>
</execution>
</executions>
<configuration>
<executable>java</executable> <!-- java must be in your PATH -->
<includeProjectDependencies>false</includeProjectDependencies>
<includePluginDependencies>false</includePluginDependencies>
<skip>${validation.skip}</skip>
<arguments>
<argument>-classpath</argument>
<classpath/> <!-- will include your class path -->
<mainClass>com.company.yourpackage.AppMain</mainClass> <!-- the class that has your main file -->
<argument>argument.xml</argument> <!-- any argument for your executable -->
</arguments>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<!-- Specify your executable jar here -->
<groupId>com.company.validator</groupId>
<artifactId>validatorId</artifactId>
<version>RELEASE</version> <!-- you can specify a fixed version here -->
<type>jar</type>
</dependency>
</dependencies>
</project>
You can run more than one executable passing its id: mvn exec:exec#MyValidator

Answer 2

I have stumbled upon the same issue - System.exit halts the maven with exec:java.
I have experimented to use the exec:exec goal, and made it work with the following configuration:
(using exec-maven-plugin 3.1.0)
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<executions>
<execution>
<id>generate-observability-docs</id>
<phase>prepare-package</phase>
<goals>
<goal>exec</goal>
</goals>
<configuration>
<executable>java</executable>
<arguments>
<argument>-jar</argument>
<argument>${settings.localRepository}/io/micrometer/micrometer-docs-generator/${micrometer-docs-generator.version}/micrometer-docs-generator-${micrometer-docs-generator.version}.jar</argument>
<argument>${micrometer-docs-generator.inputPath}</argument>
<argument>${micrometer-docs-generator.inclusionPattern}</argument>
<argument>${micrometer-docs-generator.outputPath}</argument>
</arguments>
</configuration>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>io.micrometer</groupId>
<artifactId>micrometer-docs-generator</artifactId>
<version>${micrometer-docs-generator.version}</version>
<type>jar</type>
</dependency>
</dependencies>
</plugin>