GWT-RPC傳輸Hibernate對象問題

Question

我在通過GWT中的RPC調用傳輸一個對象時出現問題。我在這個項目中使用Spring MVC和Hibernate。

這裏是實體類：

@Entity 
public class Room implements Serializable{ 
    private static final long serialVersionUID = -5924198459524011627L; 

    private Long id; 
    private String name; 
    private String description; 

    private Set<Wall> walls = new HashSet<Wall>(0); 

    public Room(){ 
    } 

    public Room(String name, String description){ 
     this.name = name; 
     this.description = description; 
    } 

    public Room(String name, String description, Set<Wall> walls){ 
     this.name = name; 
     this.description = description; 
     this.walls = walls; 
    } 

    @Id 
    @Column(name = "ROOM_ID") 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    public Long getId() { 
     return id; 
    } 
    public void setId(Long id) { 
     this.id = id; 
    } 
    public String getName() { 
     return name; 
    } 
    public void setName(String name) { 
     this.name = name; 
    } 
    public String getDescription() { 
     return description; 
    } 
    public void setDescription(String description) { 
     this.description = description; 
    } 

    @ManyToMany(cascade = CascadeType.ALL, fetch=FetchType.EAGER) 
    @JoinTable(name = "ROOM_WALL", joinColumns = {@JoinColumn(name = "ROOM_ID")}, 
      inverseJoinColumns = {@JoinColumn(name = "WALL_ID")}) 
    public Set<Wall> getWalls(){ 
     return walls; 
    } 

    public void setWalls(Set<Wall> walls){ 
     this.walls = walls; 
    } 
} 

這裏是我的RoomDAO：

@Repository 
public class RoomDAO { 

    @Autowired 
    private HibernateTemplate hibernate; 

    public Room get(Long id){ 
     return hibernate.get(Room.class, id); 
    } 

    public void delete(Room entity){ 
     hibernate.delete(entity); 
    } 

    public void save(Room entity){ 
     hibernate.saveOrUpdate(entity); 
    } 

    private Session getCurrentSession(){ 
     return hibernate.getSessionFactory().getCurrentSession(); 
    } 

    @SuppressWarnings("unchecked") 
    public List<Room> list(){ 
     String queryStr = "from "+Room.class.getSimpleName()+" fetch all properties"; 
     Query query = getCurrentSession().createQuery(queryStr); 
     System.out.println("Room list succesfull"); 
     return (List<Room>)query.list(); 
    } 

    @SuppressWarnings("unchecked") 
    public List<Wall> getWalls(Long id){ 
     String queryStr = "from "+Wall.class.getSimpleName()+" wl join wl.walls ls where ls.id=:"+id; 
     Query query = getCurrentSession().createQuery(queryStr); 
     System.out.println("Walls list succesfull"); 
     return (List<Wall>)query.list(); 
    } 
} 

這裏是錯誤信息我獲得：

com.google.gwt.user.client.rpc.SerializationException: Type 'org.hibernate.collection.PersistentSet' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = [] 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:619) 
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:539) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeClass(ServerSerializationStreamWriter.java:709) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeImpl(ServerSerializationStreamWriter.java:748) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:621) 
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126) 
    at com.google.gwt.user.client.rpc.core.java.util.Collection_CustomFieldSerializerBase.serialize(Collection_CustomFieldSerializerBase.java:44) 
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serialize(ArrayList_CustomFieldSerializer.java:39) 
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serializeInstance(ArrayList_CustomFieldSerializer.java:51) 
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serializeInstance(ArrayList_CustomFieldSerializer.java:28) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeImpl(ServerSerializationStreamWriter.java:740) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:621) 
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153) 
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:539) 
    at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:616) 
    at com.google.gwt.user.server.rpc.RPC.encodeResponseForSuccess(RPC.java:474) 
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:571) 
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:551) 
    at org.spring4gwt.server.SpringGwtRemoteServiceServlet.processCall(SpringGwtRemoteServiceServlet.java:37) 
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248) 
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487) 
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362) 
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) 
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) 
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729) 
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) 
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) 
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49) 
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) 
    at org.mortbay.jetty.Server.handle(Server.java:324) 
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505) 
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843) 
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647) 
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211) 
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380) 
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395) 
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488) 

我想問一下這個問題是由ManyToMany關係造成的，而設置爲用來映射我實體之間的關係。因爲當我傳輸一個沒有任何關係的對象（ManyToMany或OneToMany等）時，我使用Set，RPC調用可以正常工作。

難道這是解決方案來取代設置列表？我知道列表是不是有效的數據庫，但我不想重建整個項目：D

我發現這些問題可以通過使用推土機解決前。

非常感謝您的回答:)

Answer 1

這是一個已知的問題。看一下這一章爲什麼當Hibernate對象在文章Using GWT with Hibernate到達瀏覽器世界時無法被理解。