Why is Maven trying to compile my code as -source 1.3?

问题

I get this error mvn -e package in Ubuntu 12.04:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project HadoopSkeleton: Compilation failure: Compilation failure:
[ERROR] /home/jesvin/dev/hadoop/HadoopMahoutSkeleton-master/src/main/java/HadoopSkeleton/App.java:[22,8] error: generics are not supported in -source 1.3
[ERROR] 
[ERROR] (use -source 5 or higher to enable generics)
[ERROR] /home/jesvin/dev/hadoop/HadoopMahoutSkeleton-master/src/main/java/HadoopSkeleton/App.java:[53,28] error: for-each loops are not supported in -source 1.3
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project HadoopSkeleton: Compilation failure
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:213)
    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:84)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:537)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.apache.maven.plugin.CompilationFailureException: Compilation failure
    at org.apache.maven.plugin.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:516)
    at org.apache.maven.plugin.CompilerMojo.execute(CompilerMojo.java:114)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
    ... 19 more
[ERROR] 
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[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/MojoFailureException

So I guess Maven is forced to compile against an older version of Java. But why is it doing so? I just want a maven configuration that builds Mahout jars.

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-core</artifactId>
        <version>1.0.4</version>
        <!-- or whatever version -->
    </dependency>
    <dependency>
        <groupId>org.apache.mahout</groupId>
        <artifactId>mahout-core</artifactId>
        <version>0.7</version>
    </dependency>
</dependencies>

I am trying to build by https://github.com/yeahiii/HadoopMahoutSkeleton/blob/master/pom.xml

java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) Server VM (build 23.21-b01, mixed mode)

回答1:

Use Maven compiler plugin

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

回答2:

This answer to a similar qestion might answer your original question as to why.

Quoting from that post:

Configuring the Maven Compiler Plugin will fix the problem. It turns out the problem was caused by the Maven3 package in the Ubuntu repository. An alternate fix is to download Maven 3 from the Apache website which uses a more up to date Compiler plugin.

I wanted to know why this was happening when the documentation states the default Java source is 1.5. To see what mvn is using for your compiler plugin use:

mvn help:effective-pom

My Maven Compiler Plugin was 2.0.2 even though I was using Maven 3.0.4 from the Ubuntu packages. When I run the same command using Maven 3.0.4 from Apache I have a plugin version 2.3.2, which defaults to Java 1.5 as expected.

来源：https://stackoverflow.com/questions/16662830/why-is-maven-trying-to-compile-my-code-as-source-1-3

标签

maven

Hadoop

mahout