I'm very new to all things JVM and want to start a Java project that involves a Clojure library as a dependency. I've seen this question on how to run Clojure code from Java, but when I try to run the jar file after mvn package, I get cannot find symbol for variable Clojure. My code looks like this so far:
package org.example;
import clojure.java.api.Clojure;
import clojure.lang.IFn;
public class App
{
public static void main( String[] args )
{
IFn plus = Clojure.var("clojure.core", "+");
}
}
So far, my pom file looks like this:
<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>org.example</groupId>
<artifactId>project</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>poi</name>
<properties>
<maven.compiler.source>1.6</maven.compiler.source>
<maven.compiler.target>1.6</maven.compiler.target>
</properties>
<url>http://maven.apache.org</url>
<repositories>
<repository>
<id>clojars</id>
<url>https://repo.clojars.org/</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
<releases>
<enabled>true</enabled>
</releases>
</repository>
</repositories>
<build>
<plugins>
<plugin>
<groupId>com.theoryinpractise</groupId>
<artifactId>clojure-maven-plugin</artifactId>
<version>1.8.3</version>
<extensions>true</extensions>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.clojure</groupId>
<artifactId>clojure</artifactId>
<version>1.10.1</version>
</dependency>
<dependency>
<groupId>clj-python</groupId>
<artifactId>libpython-clj</artifactId>
<version>1.45</version>
</dependency>
</dependencies>
</project>
The clojure-maven-plugin seemed to download the dependencies (I watched the usual downloads fly up the screen), but still no luck on invoking Clojure after an import.
Ultimately, I hope to be able to reference libpython-clj from within Java.
Update
I tried Alan Thompson's answer and needed to run lein pom to get a pom.xml file. Then I needed to add the following to the pom at the project level to get it to mvn -q compile
<properties> <maven.compiler.source>1.6</maven.compiler.source> <maven.compiler.target>1.6</maven.compiler.target> </properties>
However, at mvn -q exec gives me long stack trace ending with
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:3.0.0:java (default-cli) on project demo: An exception occured while executing the Java class. example.Main -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:exec-maven-plugin:3.0.0:java (default-cli) on project demo: An exception occured while executing the Java class. example.Main
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:216)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:120)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:347)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:154)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:582)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.MojoExecutionException: An exception occured while executing the Java class. example.Main
at org.codehaus.mojo.exec.ExecJavaMojo.execute(ExecJavaMojo.java:311)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:132)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
... 19 more
Caused by: java.lang.ClassNotFoundException: example.Main
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:471)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:588)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:246)
at java.base/java.lang.Thread.run(Thread.java:834)
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
Update 2
It seems running mvn clean install && java -jar target/<whatever-it's called>.jar works when you add the following snippet to the pom.xml within the <plugins> section.
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>demo.Main</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
