如何拦截Struts 2 Action之间的导航？

public class TestInterceptor extends AbstractInterceptor {

    public String intercept(ActionInvocation invocation) throws Exception {
        // Do checking here, get user from session or from parameter is OK.
        // Example:
        // string returned below will be redirected to result of Struts 2 action
        String roleName = user.getRole().getName();
        if (\"admin\".equals(roleName) {
            return \"admin\";
        } else if(\"user\".equals(roleName)) {
            return \"user\";
        }

        // This means if roleName is not admin or user, the action will be invoked
        return invocation.invoke();
    }

}