A Java project set up using Maven and IntelliJ IDEA
With this part of the Java challenges project, I provide the code and settings for a Java project set up using Maven and IntelliJ IDEA.
Below, I give detailed background information on the project’s code, IntelliJ IDEA’s configuration and the used Maven configuration. I also describe several issues that can occur when setting up a Maven project, for which I provide possible solutions.
This project builds on Setting up a Java project using IntelliJ IDEA.
For demonstrative purposes, the current project contains only a single Java class called Main, which consists of a main method outputting a well-known message:
package nl.mauritssilvis.challenges.java.intellij.maven.projects.basic;
public class Main {
public static void main(String[] args) {
System.out.println("Hello world!");
}
}The basic configuration of this project is described in the IntelliJ IDEA section of Setting up a Java project using IntelliJ IDEA. Additional details regarding the IntelliJ IDEA run configurations of the current project are given in what follows.
This project comes with three run configurations.
This first run configuration is called Main and directly executes the main method of the Main class.
The other two run configurations, respectively, create a JAR and execute it.
Note that execution of the JAR fails.
This Java project is managed and built using Maven (see, e.g., the Maven section of the Java challenges project).
The Maven configuration of the current project is detailed in what follows.
In the project object model of the current project, pom.xml, the so-called project coordinates are set as follows:
<project>
<groupId>nl.mauritssilvis.challenges.java.intellij.maven.projects</groupId>
<artifactId>java-project-maven-intellij</artifactId>
<version>1.0-SNAPSHOT</version>
</project>The encoding of the source files is set to UTF-8:
<project>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
</project>Finally, the Maven compiler plugin is configured as follows:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
<configuration>
<source>21</source>
<target>21</target>
</configuration>
</plugin>
</plugins>
</build>
</project>Here, version 3.11.0 of the Maven compiler plugin is selected, which is the latest version at the time of writing. Additionally, Java 21 is selected, which is the latest long-term support (LTS) version of Java at the time of writing.
The project can be built using the following command:
mvn clean packageExecution of this command cleans the build folder, compiles the above-mentioned Java class file and packages it as a JAR file.
Alternatively, execute the following command:
mvn clean installIn addition to the previous command, this command makes the JAR available in your local Maven repository. Note that the JAR is not executable.
While setting up and building a Maven project, several issues may occur. I list several such issues below, including possible solutions. Specifically, I discuss problems related to the project object model, the Maven resources plugin, the Maven compiler plugin and the Maven JAR plugin.
Several issues may arise concerning the project object model.
When executing Maven goals, the following error may occur:
[ERROR] The goal you specified requires a project to execute but there is no POM in this directory ... Please verify you invoked Maven from the correct directory.
To solve this problem, ensure the project’s top-level directory contains a project object model file called pom.xml and that Maven is run in this directory.
When executing Maven goals, the following error may occur:
[ERROR] Some problems were encountered while processing the POMs:
[FATAL] Non-readable POM ...: input contained no data
To solve this problem, ensure the project object model, pom.xml, contains at least the project root element.
This root element can be included without any attributes:
<project></project>Alternatively, specify the optional XML preamble and namespace information:
<?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/xsd/maven-4.0.0.xsd">
</project>When executing Maven goals, the following error may occur:
[ERROR] Some problems were encountered while processing the POMs:
[ERROR] 'modelVersion' is missing. @ line 1, column 10
To solve this problem, set the model version in the project object model, pom.xml:
<project>
<modelVersion>4.0.0</modelVersion>
</project>When executing Maven goals, one or more of the following errors may occur:
[ERROR] Some problems were encountered while processing the POMs:
[FATAL] 'groupId' is missing. @ line 1, column 10
[FATAL] 'artifactId' is missing. @ line 1, column 10
[FATAL] 'version' is missing. @ line 1, column 10
To solve these problems, include the project coordinates, i.e., the group ID, the ID and the version of the artifact, in the project object model, pom.xml.
For the current project, these coordinates are defined by the following elements:
<project>
<groupId>nl.mauritssilvis.challenges.java.intellij.maven.projects</groupId>
<artifactId>java-project-maven-intellij</artifactId>
<version>1.0-SNAPSHOT</version>
</project>When executing Maven goals, the following error may occur:
[ERROR] Some problems were encountered while processing the POMs:
[FATAL] 'build.plugins.plugin.(groupId:artifactId)' artifactId of a plugin must be defined. @ line 10, column 21
To solve this problem, ensure all desired Maven plugins are identified using their artifact ID.
For example, the Maven compiler plugin can be selected with the following build section of pom.xml:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>When using Maven plugins, a warning may be shown that is similar to the following:
[WARNING] Some problems were encountered while building the effective model for nl.mauritssilvis.challenges.java.intellij.maven.projects:java-project-maven-intellij:jar:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 9, column 21
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
To prevent this warning and potential future problems with your project, select the latest Maven plugin version in the project object model, pom.xml.
For example, for the Maven compiler plugin, extend the build section of pom.xml with the following elements:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
</plugin>
</plugins>
</build>
</project>Here, version 3.11.0 of the Maven compiler plugin is selected, which is the latest version at the time of writing.
The Maven resources plugin may report at least one issue.
2.2.1 Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
The Maven resources plugin may throw a warning of the following form:
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
This warning indicates that no encoding has been set for the project files, i.e., for the source and resource files of the project.
To set the file encoding to UTF-8, include the following line in the properties section of the project object model, pom.xml:
<project>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
</project>The Maven compiler plugin may report several issues.
2.3.1 File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
Similar to the Maven resources plugin, the Maven compiler plugin may return the following warning:
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
This warning indicates that no encoding has been set for the project files, i.e., for the source and resource files of the project.
To set the file encoding to UTF-8, include the following line in the properties section in the project object model, pom.xml:
<project>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
</project>2.3.2 Source value 7 is obsolete and will be removed in a future release / Target value 7 is obsolete and will be removed in a future release
The Maven compiler plugin may return the following warnings:
[WARNING] source value 7 is obsolete and will be removed in a future release
[WARNING] target value 7 is obsolete and will be removed in a future release
To solve these warnings, ensure the Java source and target versions are explicitly set in the project object model, pom.xml, and are higher than 7.
Additionally, ensure that the target version is not smaller than the source version.
Java 21 can be selected by extending the properties section of pom.xml with the following lines:
<project>
<properties>
<maven.compiler.source>21</maven.compiler.source>
<maven.compiler.target>21</maven.compiler.target>
</properties>
</project>In addition, select the latest version of the Maven compiler plugin (3.11.0 at the time of writing) in the build section of pom.xml:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
</plugin>
</plugins>
</build>
</project>Alternatively, configure the Java target, source and Maven compiler plugin versions in the build section:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
<configuration>
<source>21</source>
<target>21</target>
</configuration>
</plugin>
</plugins>
</build>
</project>The Maven compiler plugin may halt with one of the following errors:
[ERROR] Source option 1.3 is no longer supported. Use 8 or later.
[ERROR] Source option 5 is no longer supported. Use 8 or later.
[ERROR] Source option 6 is no longer supported. Use 8 or later.
To solve these problems, explicitly set the Java source version in the project object model, pom.xml.
The source version can be set to Java 21 by extending the properties section of pom.xml with the following line:
<project>
<properties>
<maven.compiler.source>21</maven.compiler.source>
</properties>
</project>In addition, select the latest version of the Maven compiler plugin (3.11.0 at the time of writing) in the build section of pom.xml:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
</plugin>
</plugins>
</build>
</project>Alternatively, configure both the Java source and Maven compiler plugin versions in the build section:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
<configuration>
<source>21</source>
</configuration>
</plugin>
</plugins>
</build>
</project>The Maven compiler plugin may halt with one of the following errors:
[ERROR] Target option 1.1 is no longer supported. Use 8 or later.
[ERROR] Target option 5 is no longer supported. Use 8 or later.
[ERROR] Target option 6 is no longer supported. Use 8 or later.
To solve these problems, explicitly set the Java target version in the project object model, pom.xml.
The target version can be set to Java 21 by extending the properties section of pom.xml with the following line:
<project>
<properties>
<maven.compiler.target>21</maven.compiler.target>
</properties>
</project>In addition, select the latest version of the Maven compiler plugin (3.11.0 at the time of writing) in the build section of pom.xml:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
</plugin>
</plugins>
</build>
</project>Alternatively, configure both the Java target and Maven compiler plugin versions in the build section:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
<configuration>
<target>21</target>
</configuration>
</plugin>
</plugins>
</build>
</project>The Maven compiler plugin may encounter the following error while compiling:
[ERROR] source release 21 requires target release 21
To solve these problems, ensure the Java source and target versions are set in the project object model, pom.xml.
Additionally, ensure that the target version is not smaller than the source version.
Java 21 can be selected by extending the properties section of pom.xml with the following lines:
<project>
<properties>
<maven.compiler.source>21</maven.compiler.source>
<maven.compiler.target>21</maven.compiler.target>
</properties>
</project>In addition, select the latest version of the Maven compiler plugin (3.11.0 at the time of writing) in the build section of pom.xml:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
</plugin>
</plugins>
</build>
</project>Alternatively, configure the Java target, source and Maven compiler plugin versions in the build section:
<project>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.11.0</version>
<configuration>
<source>21</source>
<target>21</target>
</configuration>
</plugin>
</plugins>
</build>
</project>At least one issue may arise with the Maven JAR plugin.
When trying to execute a JAR, an error similar to the following may occur:
no main manifest attribute, in java-project-maven-intellij-1.0-SNAPSHOT.jar
To solve this problem, configure the Maven JAR plugin according to the discussion of potential Maven JAR plugin issues that is part of Creating an executable JAR using Maven and IntelliJ IDEA.
Copyright © 2021–2023 Maurits Silvis
This source code package is subject to the terms and conditions defined in the GNU General Public License v3.0 or later.