Maven配置默认JDK/JRE版本

1. settings.xml的profiles标签下配置

    <profile>
      <id>jdk-1.8</id>
      <activation>
		<activeByDefault>true</activeByDefault>
        <jdk>1.8</jdk>
      </activation>
	  <properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
	  </properties>
    </profile>