title: heroku - system.properties and java version
body: <p>I wanted to deploy my java 7 application to <code>Heroku</code> but I encountered some problems with java version. </p>
  
  <p>I added <code>system.properties</code> file in my project root directory (where <code>src</code> and <code>pom.xml</code> are) with content <code>java.runtime.version=1.7</code> but still I am getting something like this: </p>
  
  <pre><code>Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.0:compile (default-compile) on project lets-code: Fatal error compiling: invalid target release: 1.7
  </code></pre>
  
  <p>so I am a bit confused as to what to do next.</p>