我正在为我的JSF应用程序使用视图范围的托管bean。由于视图范围bean需要序列化，我已经实现了Serialiazable。但问题在于EntityManager。我尝试使用transient关键字绕过它，但我得到以下异常。
我使用了以下bean文件：
@ManagedBean
@ViewScoped
public class StatusBean2 implements Serializable {
/**
*
*/
private static final long serialVersionUID = -7528998562821856315L;
private transient EntityManager em;
public StatusBean2() {
EntityManagerFactory emf = Persistence
.createEntityManagerFactory("FreeBird");
em = emf.createEntityManager();
FacesContext context = FacesContext.getCurrentInstance();
HttpSession session = (HttpSession) context.getExternalContext()
.getSession(true);
int toIndex = 5;
session.setAttribute("toIndex", toIndex);
}
public List<Status> getStatusList() {
FacesContext context = FacesContext.getCurrentInstance();
HttpSession session = (HttpSession) context.getExternalContext()
.getSession(true);
User user = (User) session.getAttribute("userdet");
Query query = em.createQuery("SELECT s FROM Status s WHERE s.email='"// line no 49
+ user.getEmail() + "' ORDER BY s.timeMillis desc",
Status.class);
List<Status> results = query.getResultList();
Query query1 = em.createQuery("SELECT f FROM Friend f WHERE f.email='"
+ user.getEmail() + "'", Friend.class);
List<Friend> results1 = query1.getResultList();
Iterator<Friend> it = results1.listIterator();
while (it.hasNext()) {
String email = it.next().getFriendEmail();
Query query2 = em.createQuery(
"SELECT s FROM Status s WHERE s.email='" + email
+ "' ORDER BY s.timeMillis desc", Status.class);
List<Status> results2 = query2.getResultList();
results.addAll(results2);
}
Collections.sort(results);
int toIndex = (int) session.getAttribute("toIndex");
List<Status> subList = results.subList(0, toIndex);
return subList;
}
}
我在EntityManager上出现瞬态时遇到的异常如下：
javax.el.ELException: /Home.xhtml @458,24 items="#{statusBean2.statusList}": Error reading 'statusList' on type com.bean.StatusBean2
at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:111)
at com.sun.faces.facelets.tag.jstl.core.ForEachHandler.apply(ForEachHandler.java:158)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:131)
at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:162)
at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:114)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:131)
at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:162)
at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:114)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
at com.sun.faces.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:89)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
at com.sun.faces.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:79)
at com.sun.faces.facelets.impl.DefaultFacelet.apply(DefaultFacelet.java:148)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.buildView(FaceletViewHandlingStrategy.java:711)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:96)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:135)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:309)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at com.bean.StatusBean2.getStatusList(StatusBean2.java:49)
at sun.reflect.GeneratedMethodAccessor78.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at javax.el.BeanELResolver.getValue(BeanELResolver.java:87)
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:71)
at org.apache.el.parser.AstValue.getValue(AstValue.java:169)
at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:106)
答案 0 :(得分：0)
反序列化对象时未调用构造函数，因此transient字段保留为null。
你需要延迟初始化字段：
@ManagedBean
@ViewScoped
public class StatusBean2 implements Serializable {
private static final long serialVersionUID = -7528998562821856315L;
private transient EntityManager em;
private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("FreeBird");
public StatusBean2() {
FacesContext context = FacesContext.getCurrentInstance();
HttpSession session = (HttpSession) context.getExternalContext()
.getSession(true);
int toIndex = 5;
session.setAttribute("toIndex", toIndex);
}
private EntityManager em() {
if(em == null)
em = emf.createEntityManager();
return em;
}
public List<Status> getStatusList() {
FacesContext context = FacesContext.getCurrentInstance();
HttpSession session = (HttpSession) context.getExternalContext()
.getSession(true);
User user = (User) session.getAttribute("userdet");
Query query = em().createQuery("SELECT s FROM Status s WHERE s.email='"// line no 49
+ user.getEmail() + "' ORDER BY s.timeMillis desc", Status.class);
List<Status> results = query.getResultList();
Query query1 = em().createQuery("SELECT f FROM Friend f WHERE f.email='"
+ user.getEmail() + "'", Friend.class);
List<Friend> results1 = query1.getResultList();
Iterator<Friend> it = results1.listIterator();
while (it.hasNext()) {
String email = it.next().getFriendEmail();
Query query2 = em().createQuery(
"SELECT s FROM Status s WHERE s.email='" + email +
"' ORDER BY s.timeMillis desc", Status.class);
List<Status> results2 = query2.getResultList();
results.addAll(results2);
}
Collections.sort(results);
int toIndex = (int) session.getAttribute("toIndex");
List<Status> subList = results.subList(0, toIndex);
return subList;
}
}