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For some reason my stock Ubuntu 13.10 Maven installation uses old plugins. Most blatantly the compiler plugin is version 2.0.2 which defaults to Java 1.3:

$ mvn --show-version compile                                  
Apache Maven 3.0.4
Maven home: /usr/share/maven
Java version: 1.7.0_25, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-7-openjdk-amd64/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "3.11.0-14-generic", arch: "amd64", family: "unix"
[INFO] Scanning for projects...
[...]
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project simple: Compilation failure
[ERROR] [...]/simple/src/main/java/org/sonatype/mavenbook/App.java:[11,17] error: generics are not supported in -source 1.3

Compilation fails because of ArrayList<Integer> a = new ArrayList<Integer>(); which uses generics. Now I know I can force maven to use the current compiler plugin (see generics are not supported in -source 1.3) but I would rather solve the root cause than to add every plugin I use to my pom file. If there is no other solution I will add plugin specifications to a parent pom, but I would still be interested by which rational maven chooses plugin versions.

My environment: I have no settings.xml in my local m2 repository, my (stock Ubuntu) /etc/maven/m2.conf looks like this:

main is org.apache.maven.cli.MavenCli from plexus.core

set maven.home default ${user.home}/m2

[plexus.core]
optionally ${maven.home}/lib/ext/*.jar
load       ${maven.home}/lib/*.jar

And my /etc/maven/settings.xml is essentially empty except for a few comments and empty xml tags. The projects pom is the default generated by mvn archetype:generate -DgroupId=org.sonatype.mavenbook -DartifactId=simple -Dpackage=org.sonatype.mavenbook -Dversion=1.0-SNAPSHOT:

<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>org.sonatype.mavenbook</groupId>
  <artifactId>simple</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>simple</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

Any advice?

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Perseids
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1 Answers1

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You can (and should) specify the Maven compiler plugin manually in your pom.xml

<build>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <configuration>
                <source>1.7</source>
                <target>1.7</target>
            </configuration>
        </plugin>
    </plugins>
</build>

I have no idea why Maven 3.0.4 uses such an early Maven compiler plugin version but I don't think it's an Ubuntu specific problem. I don't know a general solution bould it would require local configuration. You want to avoid that because it makes your build platform dependent. The advantage of explicitly specifying this in your pom is that you can just build your project on any other machine without facing the same issue again.

If don't want to do this in every project you can use a parent pom. See default maven compiler setting

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André Stannek
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