Exception while building Scala-Maven project on IntelliJ - scala

Question

I am trying to build a Scala-Maven project on IntelliJ IDEA. Right after creating the project, it says build successful. This is how my pom.xml looks like:
<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>com.dbloads.pgms</groupId>
<artifactId>Arts</artifactId>
<version>1.0-SNAPSHOT</version>
<inceptionYear>2008</inceptionYear>
<properties>
<scala.version>2.7.0</scala.version>
</properties>
<dependencies>
<dependency>
<groupId>org.scala-lang</groupId>
<artifactId>scala-library</artifactId>
<version>${scala.version}</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.4</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.specs</groupId>
<artifactId>specs</artifactId>
<version>1.2.5</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/scala</sourceDirectory>
<testSourceDirectory>src/test/scala</testSourceDirectory>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.4.0</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
<args>
<arg>-target:jvm-1.5</arg>
</args>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-eclipse-plugin</artifactId>
<configuration>
<downloadSources>true</downloadSources>
<buildcommands>
<buildcommand>ch.epfl.lamp.sdt.core.scalabuilder</buildcommand>
</buildcommands>
<additionalProjectnatures>
<projectnature>ch.epfl.lamp.sdt.core.scalanature</projectnature>
</additionalProjectnatures>
<classpathContainers>
<classpathContainer>org.eclipse.jdt.launching.JRE_CONTAINER</classpathContainer>
<classpathContainer>ch.epfl.lamp.sdt.launching.SCALA_CONTAINER</classpathContainer>
</classpathContainers>
</configuration>
</plugin>
</plugins>
</build>
<reporting>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.4.0</version>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
</configuration>
</plugin>
</plugins>
</reporting>
</project>
Next I tried to add the compiler options in project like below:
Once added and when I click the RUN button, I get the below error message:
[ERROR] Plugin net.alchim31.maven:scala-maven-plugin:3.4.0 or one of its dependencies could not be resolved: Failed to read artifact descriptor for net.alchim31.maven:scala-maven-plugin:jar:3.4.0: Could not transfer artifact net.alchim31.maven:scala-maven-plugin:pom:3.4.0 from/to central (https://repo.maven.apache.org/maven2): PITC-Zscaler-EMEA-Amsterdam3PR.proxy.corporate.ge.com: Unknown host PITC-Zscaler-EMEA-Amsterdam3PR.proxy.corporate.ge.com -> [Help 1]
I am using the jdk version: 1.8.0_172 and I have added the Scala plugin directly from the plugins. Hence it is the latest version of the Scala.
Could anyone let me know how can I fix this problem.

Answer 1

It looks like you need to configure Maven and IntelliJ to use network proxy settings, since it looks like you might be behind a corporate firewall.
Maven has the ability to configure a proxy through its settings (in ~/.m2/settings.xml on Unix-like systems, or %HOME%\.m2\settings.xml on Windows), as follows:
<settings ...>
.
.
<proxies>
<!-- You can have one of these for each possible proxy. -->
<proxy>
<active>true</active>
<!-- Pick some ID for your proxy here. -->
<id>corp-proxy</id>
<!-- Choose your protocol here. E.g. "http", "socks4" or "socks5" -->
<protocol>http</protocol>
<!-- Specify the proxy server name (or IP address) and port of your proxy here. -->
<host>proxy.example.com</host>
<port>8080</port>
<!-- Identify any hosts here that you can access directly. It's unlikely that you'll
need this unless you have a proxy repository (such as Nexus, Artifactory, etc.) on
your corporate network. -->
<nonProxyHosts>www.google.com|*.example.com</nonProxyHosts>
<!-- The following fields are only necessary if required by your proxy. If you need to
enter your own username and password, make sure you do not add this file to version
control! -->
<username>proxyuser</username>
<password>somepassword</password>
</proxy>
</proxies>
.
.
</settings>
Meanwhile, IntelliJ is configured to use proxies through its settings. Refer to this answer for further details. (Note that setting proxy information via the JAVA_OPTS environment variable will work for running any Java/Scala/JVM application that needs to access the Internet via a proxy.)
Alternatively, if your proxy settings are configured correctly or are not required, it might be a temporary network connection issue, so make sure you have an Internet connection and try again. (The exception is a failure by Maven to download the plugin from the Maven central repository.)
BTW, the version of Scala you have specified—2.7.0—is ancient and almost certainly will not work with JDK 8. Either use an older JDK or a more recent version of Scala (the current release is 2.12.6).
Note that if you need to work with the current version of Apache Spark, you must currently use Scala 2.11.x - the most recent release being 2.11.12.
UPDATE:
From your comments, it seems there is some confusion about the roles played by Maven, the scala-maven-plugin, IntelliJ and the IntelliJ Scala plugin, so I'll quickly summarize them here. Please bear with me if I cover topics you're already familiar with...
Maven is a system for building and publishing software. (It actually does a lot more than just that, which is why Maven describes itself as project management software.) It allows developers to specify, in a single place, all of their software's dependencies (third-party libraries used by the software), which Maven downloads as required from the Central Maven Repository—mostly open-source—or from other, private repositories, as required. Further settings control how compilers are configured, tests are run, reports generated, etc.
Maven was developed primarily for development of Java-language projects. The scala-maven-plugin provides support for the Scala language and compiler within Maven. It is this plugin that downloads the version of the Scala compiler specified by your project and uses it to compile and build your sources.
If you look at your Maven project's pom.xml file, you will notice the following lines in the build section:
<project ...>
...
<build>
...
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.4.0</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
<args>
<arg>-target:jvm-1.5</arg>
</args>
</configuration>
</plugin>
...
</build>
...
</project>
and again in the reporting section:
<project ...>
...
<reporting>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.4.0</version>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
</configuration>
</plugin>
</plugins>
</reporting>
</project>
In both cases, there is a line that reads <scalaVersion>${scala.version}</scalaVersion>, which tells Maven which version of Scala you want to use. The plugin then uses this version of the Scala compiler, and has Maven download it to a cached, local repository on your machine (typically, in C:\Users\{your account}\.m2 on a Windows machine). Note that both Maven and the scala-maven-plugin will ignore any versions of Scala you have installed on your machine.
So which version of Scala is the plugin going to download for you? The value ${scala.version} states that the version number is stored as the value of a property named scala.version. Your pom.xml file also has lines, near the top, that create this property:
<project ...>
...
<properties>
<scala.version>2.7.0</scala.version>
</properties>
...
</project>
So, you can see that you will use version 2.7.0 of the Scala compiler. If you want to use the latest Scala version, you should change this to:
<project ...>
...
<properties>
<scala.version>2.12.6</scala.version>
</properties>
...
</project>
OK, so now you will be using the latest version of the Scala compiler. Now let's move on to IntelliJ...
IntelliJ IDEA is an Integrated Development Environment (IDE), primarily aimed at development with the Java language. It provides syntax highlighting, smart code completion, and other features to simplify the process of writing code. In order to provide those features for the Scala programming language, you need to install its Scala plugin.
You can configure IntelliJ to use any version of Scala that you have installed on your machine. IntelliJ will then know how to compile, build and run your software and can work without using your Maven project object model (POM) file's build definition.
However, one of the reasons for using Maven is to ensure a consistent build environment for developing a project, so that it is not at the whim of whatever each developer may or may not have installed on their machine. For this reason, if a project uses Maven, it's a good idea to tell IntelliJ. That way, IntelliJ can use Maven's pom.xml file to specify the version of the compiler, download dependencies, configure the compiler settings, etc.
So, the above information should help you to get up-and-running with your project, working with your corporation's network proxy and using the latest version of Scala, using Maven and IntelliJ.