在过滤器中访问JSF（2.3）托管bean

Question

我有一个注释为@SessionScoped的Bean：

@ManagedBean(name="bUser")
@SessionScoped
public class BUser implements Serializable {
    private Integer userId = 0;

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }
}

我有一个过滤器类（javax.servlet.Filter），它将用作路由器：

public class LoginFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        // Get bUser bean property

        chain.doFilter(request, response);
    }

    // [...]
}

如何访问bUser bean及其属性？