过滤器不会初始化EntityManager。

Question

我正在尝试使用Open Session in View模式，但每次我尝试在我的ManagedBean中捕获EntityManager时，entityManager都会变成NULL。这是我的做法：

package filters;

// imports..    


public class JPAFilter implements Filter {

    private EntityManagerFactory factory;

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

        EntityManager entityManager = this.factory.createEntityManager();
        request.setAttribute("entityManager", entityManager);
        entityManager.getTransaction().begin();

        chain.doFilter(request, response);

        try {
            entityManager.getTransaction().commit();
        } catch (Exception e) {
            entityManager.getTransaction().rollback();
            throw new ServletException(e);
        } finally {
            entityManager.close();
        }
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.factory = Persistence.createEntityManagerFactory("copadomundo");

    }

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

}

这是我的托管Bean:

package managedbeans;

// imports ..

@ManagedBean
public class PlayerBean {

    @ManagedProperty(value = "#{entityManager}")
    private EntityManager entityManager;

    private Player player = new Player();

    private Long teamID;

    private List<Player> players = new ArrayList<Player>();

    public void add() {
        TeamRepository selecaoRepository = new TeamRepository(this.entityManager);
        Team selecao = selecaoRepository.search(this.teamID);
        this.player.setTeam(selecao);

        PlayerRepository playerRepository = new PlayerRepository(this.entityManager);
        playerRepository.adiciona(this.player);

        this.player = new Player();
        this.players = null;
    }

    public void remove(Player player) {
        PlayerRepository repository = new PlayerRepository(this.entityManager);
        repository.remove(player);
        this.players = null;
    }

    // GETTERS AND SETTERS
    public List<Player> getPlayeres() {
        if (this.players == null) {

            PlayerRepository repository = new PlayerRepository(
                    this.entityManager);
            this.players = repository.getPlayeres();
        }
        return this.players;
    }

    public EntityManager getEntityManager() {
        return entityManager;
    }

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    public Player getPlayer() {
        return player;
    }

    public void setPlayer(Player player) {
        this.player = player;
    }

    public Long getTeamID() {
        return teamID;
    }

    public void setTeamID(Long teamID) {
        this.teamID = teamID;
    }

    public void setPlayeres(List<Player> players) {
        this.players = players;
    }
}

这是我的web.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <display-name>WorldCup</display-name>
    <welcome-file-list>
        <welcome-file>index.xhtml</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>Faces Servlet</servlet-name>
        <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Faces Servlet</servlet-name>
        <url-pattern>*.xhtml</url-pattern>
    </servlet-mapping>
    <filter>
        <filter-name>LoginFilter</filter-name>
        <filter-class>jpa.LoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>LoginFilter</filter-name>
        <servlet-name>Faces Servlet</servlet-name>
    </filter-mapping>
    <filter>
        <filter-name>JPAFilter</filter-name>
        <filter-class>jpa.JPAFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>JPAFilter</filter-name>
        <servlet-name>Faces Servlet</servlet-name>
    </filter-mapping>
    <error-page>
        <exception-type>java.lang.Exception</exception-type>
        <location>/error.xhtml</location>
    </error-page>
</web-app>

有任何想法为什么会发生这种情况吗？

更新： 在搜索了关于JPA、Hibernate和EJB的所有地方之后，我终于找到了一篇好的教程（按照以下顺序理解正在做什么，好吗？）：

安装并配置 Eclipse 和 Oracle Glassfish 3.1 的 MySQL：Install and Configure MySQL for Eclipse and Oracle Glassfish 3.1 使用 JSF 2.0 构建用户注册表单：Building a User Registration Form using JSF 2.0 使用 JSF 2.0 进行数据验证和转换：Validation and Conversion of Data Using JSF 2.0 使用 EJB 3.0 和 JPA 2.0 进行数据库持久化：Using EJB 3.0 and JPA 2.0 for Database Persistence

- Valter Silva

Answer 1

那只有在您的PlayerBean也是请求范围内时才能起作用。如果它是视图范围内的，则任何手动创建的请求范围属性都将被忽略并且不会注入，因为此构造不允许这样做。您只能注入与接收器相同或更广泛范围的JSF托管属性。

根据您的问题历史，我知道您正在使用Glassfish 3。为什么不使用EJB呢？这样容器将自行处理事务，您根本不需要拥有这样的过滤器。您可以通过@PersistenceContext注入EntityManager。

非常简单。只需创建以下EJB类：

@Stateless
public class PlayerService {

    @PersistenceContext
    private EntityManager em;

    public Player find(Long id) {
        return em.find(Player.class, id);
    }

    public List<Player> list() {
        return em.createQuery("SELECT p FROM Player p", Player.class).getResultList();
    }

    public void create(Player player) {
        em.persist(player);
    }

    public void update(Player entity) {
        em.merge(player);
    }

    public void delete(Player player) {
        em.remove(em.contains(player) ? player : em.merge(player));
    }

    // ...
}

(在Glassfish 3上不需要进一步的配置)

然后您可以在JSF托管的bean中按如下方式使用它:

@ManagedBean
@ViewScoped
public class PlayerBean {

    private List<Player> players;

    @EJB
    private PlayerService playerService;

    @PostConstruct
    public void init() {
        players = playerService.list();
    }

    // ...
}

- BalusC

---

开放式会话视图模式用于避免在表示层中使用分离的对象，从而避免担心延迟初始化异常。 - JB Nizet

我明白了@BalusC，谢谢伙计，哇哦哦哦哦哦哦哦哦哦！=] 终于。 - Valter Silva