[JAVA] Create command line app with maven

Create a minimal Maven project

If you create a Maven project with the defaults in Eclipse (STS to be exact), the POM will look like this.

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>test</groupId>
  <artifactId>test</artifactId>
  <version>0.0.1-SNAPSHOT</version>
</project>

Create a class appropriately ...

Main.java

package jp.demo;

public class Main {
	public static void main(String[] args){
		System.out.println("### START ###");
		System.out.println("### END ###");
	}
}

When you run ...

When I run Jar after maven install, I get angry if there is no manifest.

Command line

C:\sts\workspace\simple_maven\target>java -jar test-0.0.1-SNAPSHOT.jar
test-0.0.1-SNAPSHOT.jar does not have main manifest attribute
Generate manifest file

Specify mainClass

Therefore, specify the mainClass tag in order from the build tag as shown below. In the mainClass tag, specify the main class from the package.

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>test</groupId>
	<artifactId>test</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-jar-plugin</artifactId>
				<configuration>
					<archive>
						<manifest>
							<mainClass>jp.demo.Main</mainClass>
						</manifest>
					</archive>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

When I run it again ...

After maven install, when I executed it again, it ended normally.

Command line

C:\sts\workspace\simple_maven\target>java -jar test-0.0.1-SNAPSHOT.jar
### START ###
### END ###

If you get an error like this ...

-"Please use -source 7 or later to enable the diamond operator" -"Please use -source 8 or higher to enable lambda expressions"

Since the version of the compiler is low, let's add the following.

pom.xml

	<properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
	</properties>

If you get this error 2 ...

--"Unknown Error" at the beginning of POM.xml

Let's add the following to properties as above. (It seems to be a bug of maven-jar-plugin 3.1.2. It came out in another project.)

pom.xml

	<maven-jar-plugin.version>3.1.1</maven-jar-plugin.version>

reference: https://bugs.eclipse.org/bugs/show_bug.cgi?id=547409

Finally

Now this.

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>test</groupId>
	<artifactId>test</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
	</properties>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-jar-plugin</artifactId>
				<configuration>
					<archive>
						<manifest>
							<mainClass>jp.demo.Main</mainClass>
						</manifest>
					</archive>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>