This, and many other building problems in Talend O.S. 6.x (both ESB and DI products) are related with the <source> and <target> values, in the pom.xml of the .Java project, within the Talend workspace folder.
Try to set them to the JDK/JRE You configured in Talend properties. By example, if You configured Talend product to start and to build with JDK/JRE v 1.8, You should set the mentioned tags as follows:
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
Moreover, remember that when a Talend product builds (generates Java sources and compiles 'em) a Job, it's using Maven (behind the scenes) with the settings as defined in the following file:
[Talend_install_dir]/configuration/maven_user_settings.xml