Here is an example for adding toolbar, you can add your menu using the same example.
Please look into this page https://www.eclipse.org/che/docs/assemblies/sdk-actions/index.html
@Extension(title = "Sample Actions Extension", version = "1.0.0")
public class SampleActionsExtensions {
@Inject
public SampleActionsExtensions(HelloWorldAction helloWorldAction, ActionManager actionManager) {
actionManager.registerAction("helloWorldAction", helloWorldAction);
actionManager.registerAction("helloWorldActionWithIcon", helloWorldActionWithIcon);
/...
DefaultActionGroup sampleGroup = new DefaultActionGroup("Sample actions", true, actionManager);
sampleGroup.add(helloWorldAction);
// add sample group after help menu entry
DefaultActionGroup mainMenu = (DefaultActionGroup)actionManager.getAction(GROUP_MAIN_MENU);
mainMenu.add(sampleGroup);
// add the sample group to the beginning of the toolbar as well
DefaultActionGroup toolbar = (DefaultActionGroup)actionManager.getAction(IdeActions.GROUP_MAIN_TOOLBAR);
toolbar.add(helloWorldActionWithIcon);
/...
}
}