JSF和JPA:在持久性/模型层中使用Filter

我正在练习JSF和JPA,下面的例子中有一个用于模型/持久层的过滤器类:

@WebFilter(servletNames = { "Faces Servlet" })
public class JPAFilter implements Filter {

    private EntityManagerFactory factory;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.factory = Persistence.createEntityManagerFactory("K19-Futebol-PU");
    }

    @Override
    public void destroy() {
        this.factory.close();
    }

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

        // in
        EntityManager manager = this.factory.createEntityManager();
        request.setAttribute("EntityManager", manager);
        manager.getTransaction().begin();
        // in

        // FACES SERVLET
        chain.doFilter(request, response);
        // FACES SERVLET

        // out
        try {
            manager.getTransaction().commit();
        } catch (Exception e) {
            manager.getTransaction().rollback();
        } finally {
            manager.close();
        }
        // out
    }
}

运行应用程序时出现NullPointerException:

SEVERE: Error Rendering View[/times.xhtml]
javax.el.ELException: /lista-de-times.xhtml @5,51 rendered="#{empty timeBean.times}": java.lang.NullPointerException
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:114)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)

    at filters.JPAFilter.doFilter(JPAFilter.java:42)

    Caused by: java.lang.NullPointerException
    at repositories.TimeRepository.getLista(TimeRepository.java:44)
    at managedbeans.TimeBean.getTimes(TimeBean.java:68)

    ... 43 more

WARNING: StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
    at repositories.TimeRepository.getLista(TimeRepository.java:44)

    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at filters.JPAFilter.doFilter(JPAFilter.java:42)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)

这是“存储库”类:

public class TimeRepository {

    private EntityManager manager;

    public TimeRepository(EntityManager manager) {
        this.manager = manager;
    }

    public void adiciona(Time time) {
        this.manager.persist(time);
    }

    @SuppressWarnings("unchecked")
    public void remove(Long id) {
        Time time = this.procura(id);
        Query query = this.manager.createQuery("select x from Jogador x");
        List<Jogador> jogadores = query.getResultList();
        for (Jogador jogador : jogadores) {
            jogador.setTime(null);
        }
        this.manager.remove(time);
    }

    public Time atualiza(Time time) {
        return this.manager.merge(time);
    }

    public Time procura(Long id) {
        return this.manager.find(Time.class, id);
    }

    @SuppressWarnings("unchecked")
    public List<Time> getLista() {
        Query query = this.manager.createQuery("select x from Time x");
        return query.getResultList();
    }
}

表中已经有一些数据了,我认为这个问题与JSF生命周期和过滤器类有关,但我不知道如何解决它。

有人能帮帮我吗?我还引用了关于使用所描述的过滤器的评论,我的意思是,这是一个好的实践,一个“优雅的解决方案”吗?

提前谢谢。

以下是与存储库相关的TimeBean类:

@ManagedBean
public class TimeBean {

    private Time time = new Time();
    private List<Time> times;

    public void adiciona() {
        EntityManager manager = this.getManager();
        TimeRepository repository = new TimeRepository(manager);
        if (this.time.getId() == null) {
            repository.adiciona(this.time);
        } else {
            repository.atualiza(this.time);
        }
        this.time = new Time();
        this.times = null;
    }

    public void preparaAlteracao() {
        Map< String, String> params =
                FacesContext.getCurrentInstance().getExternalContext().Ã
                - getRequestParameterMap();
        Long id = Long.parseLong(params.get("id"));
        EntityManager manager = this.getManager();
        TimeRepository repository = new TimeRepository(manager);
        this.time = repository.procura(id);
    }

    public void remove() {
        Map< String, String> params =
                FacesContext.getCurrentInstance().getExternalContext().Ã
                - getRequestParameterMap();
        Long id = Long.parseLong(params.get("id"));
        EntityManager manager = this.getManager();
        TimeRepository repository = new TimeRepository(manager);
        repository.remove(id);
        this.times = null;
    }

    public List<Time> getTimes() {
        if (this.times == null) {
            EntityManager manager = this.getManager();
            TimeRepository repository = new TimeRepository(manager);
            this.times = repository.getLista();
        }
        return this.times;
    }

    private EntityManager getManager() {
        FacesContext fc = FacesContext.getCurrentInstance();
        ExternalContext ec = fc.getExternalContext();
        HttpServletRequest request = (HttpServletRequest) ec.getRequest();
        return (EntityManager) request.getAttribute(" EntityManager ");
    }
    // GETTERS E SETTERS
}