title: Failed to deploy to Google App Engine because --use_java7 flag has not been set
body: <blockquote>
    <p>------------ Deploying frontend ------------</p>
    
    <p>Preparing to deploy:  Created staging directory at:
    'C:\Users\ADMINI~1\AppData\Local\Temp\appcfg2555411734473986257.tmp'
    java.lang.RuntimeException: The application contains Java 7 classes,
    but the --use_java7 flag has not been set.</p>
    
    <p>Debugging information may be found in
    C:\Users\Administrator\AppData\Local\Temp\appengine-deploy7182870224187999057.log</p>
  </blockquote>
  
  <p>Debug Log:</p>
  
  <blockquote>
    <p>Unable to update:
    java.lang.RuntimeException: The application contains Java 7 classes, but the --use_java7 flag has not been set.
        at com.google.appengine.tools.admin.Application.createStagingDirectory(Application.java:576)
        at com.google.appengine.tools.admin.AppAdminImpl.doUpdate(AppAdminImpl.java:370)
        at com.google.appengine.tools.admin.AppAdminImpl.update(AppAdminImpl.java:53)
        at com.google.appengine.eclipse.core.proxy.AppEngineBridgeImpl.deploy(AppEngineBridgeImpl.java:433)
        at com.google.appengine.eclipse.core.deploy.DeployProjectJob.runInWorkspace(DeployProjectJob.java:148)
        at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:38)
        at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)</p>
  </blockquote>
  
  <p>I'm attempting to deploy a google app to my google app engine account and eclipse is giving me this error. It seems rather straight forward, but I can't find where to set a flag for java7. </p>
  
  <p>I'm using the latest version of Eclipse (Juno Service Release 1) and my google plugin is 4.2.</p>