java - Error of source value 1.5 is obsolete and will be removed in a future release

Question

I use scala-maven-plugin to compile a project with both scala and java code. I already set the source and target to 1.7, but not sure why maven still use 1.5.

Here's my plugin in pom.xml

<plugin>
        <groupId>net.alchim31.maven</groupId>
        <artifactId>scala-maven-plugin</artifactId>
        <version>3.2.2</version>
        <executions>
          <execution>
            <id>eclipse-add-source</id>
            <goals>
              <goal>add-source</goal>
            </goals>
          </execution>
          <execution>
            <id>scala-compile-first</id>
            <phase>process-resources</phase>
            <goals>
              <goal>compile</goal>
            </goals>
          </execution>
          <execution>
            <id>scala-test-compile-first</id>
            <phase>process-test-resources</phase>
            <goals>
              <goal>testCompile</goal>
            </goals>
          </execution>
          <execution>
            <id>attach-scaladocs</id>
            <phase>verify</phase>
            <goals>
              <goal>doc-jar</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <scalaVersion>${scala.version}</scalaVersion>
          <recompileMode>incremental</recompileMode>
          <useZincServer>true</useZincServer>
          <args>
            <arg>-unchecked</arg>
            <arg>-deprecation</arg>
            <arg>-feature</arg>
          </args>
          <jvmArgs>
            <jvmArg>-Xms1024m</jvmArg>
            <jvmArg>-Xmx1024m</jvmArg>
            <jvmArg>-XX:PermSize=${PermGen}</jvmArg>
            <jvmArg>-XX:MaxPermSize=${MaxPermGen}</jvmArg>
          </jvmArgs>
          <javacArgs>
            <javacArg>-source</javacArg>
            <javacArg>1.7</javacArg>
            <javacArg>-target</javacArg>
            <javacArg>1.7</javacArg>
            <javacArg>-Xlint:all,-serial,-path,-options</javacArg>
          </javacArgs>
        </configuration>
      </plugin>

And this the output error I see

[warn]   implicit def toDisplayTraversableFunctions[T <: Product](traversable: Traversable[T]): DisplayTraversableFunctions[T] = new DisplayTraversableFunctions[T](traversable)
[warn]                ^
[warn] two warnings found
[error] /Users/jzhang/github/zeppelin/spark/src/main/java/org/apache/zeppelin/spark/DepInterpreter.java:158: error: diamond operator is not supported in -source 1.5
[error]     settings.explicitParentLoader_$eq(new Some<>(Thread.currentThread()

But I am sure I am usign JDK8.

java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

Maven also use JDK8

Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=1024M; support was removed in 8.0
Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-11T00:41:47+08:00)
Maven home: /Users/jzhang/Java/lib/apache-maven-3.3.9
Java version: 1.8.0_45, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.11.6", arch: "x86_64", family: "mac"

Answer 1

The quintessential way to set the compiler source and target versions these days seems to be use these pre-defined properties:

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

As you already noted, these default to 1.5 in maven. This is because Maven was always about "convention over configuration" and this default value was defined when Java 1.5 was still shiny and new. Unfortunately this has been difficult to change because any existing projects that still depend on Java 1.5 (and had not specified these values) could break.