To inject a Seam component you may use the @In annotation.
@In private User _user;
If you want to outject your component back to the context, please use @Out annotation.
@Out private User user;
Since @Out@Out requires non-null value, you can make Seam to create an instance of the component if there is none existing instance by using @In(create=true)
@In(create=true) @Out private User user;
Furthermore you can inject the value of an expression:
@In("#{user.username}") public String _username();
The el binding prefix allows you to use EL expressions in Tapestry templates.
${el:user.getUsername()}