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

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>