使用 ContentFlow (coverflow) 显示数据库图像 IllegalStateException 错误

我目前正在使用第三方图像 coverflow (http://www.jacksasylum.eu/ContentFlow/) 来显示保存在数据库中的图像。为此，我使用 Java、JPA 和 Richfaces。我已经设置了一个图像 servlet 来处理图像显示。我设置了 Richfaces 数据表，并且只想在封面流中显示所选记录的图像。此功能就是为了执行此操作而准备的。我有一个命令按钮可以在 OutputPanel 中渲染图像封面流。在实施封面流程之前，我的图像在页面下方正确显示，没有错误。所以，我知道我的底层功能可以按预期工作。问题是，当我按照指示在 img 标签周围放置特定的 div 标签来实现 coverflow 时，出现以下错误：

Error Rendering View[/index.xhtml]: java.lang.IllegalStateException: Cannot create a session after the response has been committed
at org.apache.catalina.connector.Request.doGetSession(Request.java:2636) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.connector.Request.getSession(Request.java:2375) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:841) [jbossweb-7.0.10.Final.jar:]
at com.sun.faces.context.ExternalContextImpl.getSession(ExternalContextImpl.java:155) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at javax.faces.context.ExternalContextWrapper.getSession(ExternalContextWrapper.java:396) [jboss-jsf-api_2.1_spec-2.0.0.Final.jar:2.0.0.Final]
at com.sun.faces.renderkit.ServerSideStateHelper.writeState(ServerSideStateHelper.java:175) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.renderkit.ResponseStateManagerImpl.writeState(ResponseStateManagerImpl.java:122) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.application.StateManagerImpl.writeState(StateManagerImpl.java:166) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.application.view.WriteBehindStateWriter.flushToWriter(WriteBehindStateWriter.java:225) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:419) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288) [jboss-jsf-api_2.1_spec-2.0.0.Final.jar:2.0.0.Final]
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288) [jboss-jsf-api_2.1_spec-2.0.0.Final.jar:2.0.0.Final]
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139) [jsf-impl-2.1.5-jbossorg-1.jar:2.1.5-SNAPSHOT]
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594) [jboss-jsf-api_2.1_spec-2.0.0.Final.jar:2.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.10.Final.jar:]
at org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62) [weld-core-1.1.5.AS71.Final.jar:2012-02-10 15:31]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:280) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.10.Final.jar:]
at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.1.0.Final.jar:7.1.0.Final]
at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:154) [jboss-as-web-7.1.0.Final.jar:7.1.0.Final]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.10.Final.jar:]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.10.Final.jar:]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.10.Final.jar:]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:671) [jbossweb-7.0.10.Final.jar:]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:930) [jbossweb-7.0.10.Final.jar:]
at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_32]

这是我的一些代码：

ImgServlet.java

 /**
   * Servlet implementation class ImgServlet
   */
    @WebServlet(name = "ImgServlet", urlPatterns = {"/ImgServlet/*"})
    public class ImgServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Inject
    Screenshot model;
        @PersistenceUnit(unitName = "primary")
    private EntityManagerFactory emf; 

    public ImgServlet() {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter writer = response.getWriter();
        ServletContext sc = getServletContext();

        String classString = "Screenshot";
        String idString = request.getParameter("id");

        if (classString == null || classString.isEmpty() || idString == null || idString.isEmpty()) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
            return;
        }

        Long id = Long.parseLong(idString.trim());
        PhotoInterface entry = null;

        EntityManager em = null;

        try {
            em = emf.createEntityManager();
        } catch (Throwable e1) {
            e1.printStackTrace();
        } 

        try {
            entry = em.find(Screenshot.class, id);
        } catch (Exception ex) {
            //Log.log(ex.getMessage());
        }

        if (entry == null) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
            return;
        }

        ServletOutputStream out = null;

        try {
            response.reset();

             // It works ok without setting any of these...
            //response.setContentType(image.getContentType());
            //response.setHeader("Content-Length", String.valueOf(image.getLength()));
            //response.setHeader("Content-Disposition", "inline; filename=\"" + image.getName() + "\"");
            response.setContentType("image/png");

            out = response.getOutputStream();

            if (entry.getPng() != null && entry.getPng().length != 0) {
                out.write(entry.getPng());
                getServletContext().log("Found png!!");
            }
            else 
                getServletContext().log("png is NULL!!!");
        } catch (IOException e) {
            getServletContext().log("Error finding png!!!");
        } finally {
            close(out);
        }

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    private static void close(Closeable resource) {
        if (resource != null) {
            try {
                resource.close();
            } catch (IOException e) {
                // Do your thing with the exception. Print it, log it or mail it.
            }
        }
    }
}

contentflow_src.js- 用于渲染封面流的 javascript，可以在以下位置查看示例

http://www.jacksasylum.eu/ContentFlow/download.php

目前，这在我的 xhtml 中有效（outputPanel 内没有 ContentFlow Div 标签）：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"  
    xmlns:h="http://java.sun.com/jsf/html"  
    xmlns:f="http://java.sun.com/jsf/core"  
    xmlns:p="http://primefaces.org/ui">  

    <ui:composition 
                xmlns:ui="http://java.sun.com/jsf/facelets"
                xmlns:f="http://java.sun.com/jsf/core"
                xmlns:h="http://java.sun.com/jsf/html"
                xmlns:a4j="http://richfaces.org/a4j"
                xmlns:rich="http://richfaces.org/rich"
                xmlns:my="http://java.sun.com/jsf/composite/components"
                xmlns:s="http://jboss.com/products/seam/taglib"
                >
    <h:head>  
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <h:outputStylesheet name="screen.css" library="css"/> 
        <script language="JavaScript" type="text/javascript" src="contentflow_src.js" load="slideshow lightbox">
        </script>
    </h:head>  
    <h:body>
       <h:form id="form"> 
        <p:dataTable var="scrshot">
          ....................
          ....................
         </p:dataTable>

          <p:commandButton id="viewDetails" value="View Selected Screenshots" icon="ui-icon-search"  
                             update=":form:imgBlock"/> 

          <p:outputPanel id="imgBlock" layout="block"> 
             <a4j:repeat var="img" value="#{screenshotListProducer.selectedScreenshots}">
               <img src="ImgServlet?id=#{img.id}" title="#{img.time}"/>
             </a4j:repeat>
          </p:outputPanel>
         </h:form>                            
    </h:body> 
    </ui:composition> 
</html>

这在我的 xhtml 中不起作用（在通过在 outputPanel 内使用 Div 标签包装来实现 ContentFlow 之后）并触发错误：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"  
    xmlns:h="http://java.sun.com/jsf/html"  
    xmlns:f="http://java.sun.com/jsf/core"  
    xmlns:p="http://primefaces.org/ui">  

    <ui:composition 
                xmlns:ui="http://java.sun.com/jsf/facelets"
                xmlns:f="http://java.sun.com/jsf/core"
                xmlns:h="http://java.sun.com/jsf/html"
                xmlns:a4j="http://richfaces.org/a4j"
                xmlns:rich="http://richfaces.org/rich"
                xmlns:my="http://java.sun.com/jsf/composite/components"
                xmlns:s="http://jboss.com/products/seam/taglib"
                >
    <h:head>  
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <h:outputStylesheet name="screen.css" library="css"/> 
        <script language="JavaScript" type="text/javascript" src="contentflow_src.js" load="slideshow lightbox">
        </script>
    </h:head>  
    <h:body>
       <h:form id="form"> 
        <p:dataTable var="scrshot">
          ....................
          ....................
         </p:dataTable>

          <p:commandButton id="viewDetails" value="View Selected Screenshots" icon="ui-icon-search"  
                             update=":form:imgBlock"/> 

          <p:outputPanel id="imgBlock" layout="block"> 
           <div class="ContentFlow" id="ContentFlow">
            <div class="flow">
             <a4j:repeat var="img" value="#{screenshotListProducer.selectedScreenshots}">
              <div class="item">
               <img src="ImgServlet?id=#{img.id}" title="#{img.time}"/>
              </div>
             </a4j:repeat>
            </div>
           </div>
          </p:outputPanel>
         </h:form>                            
    </h:body> 
    </ui:composition> 
</html>

对所有代码感到抱歉。如果有人可以提供帮助，我们将不胜感激！我花了好几天的时间试图让 ContentFlow 在我的会话中正常运行。