重要通知:自fixed(社区发行版)PrimeFaces 5.2 final到2015年4月8日，此问题已成为released。因此，如果您碰巧使用了该版本或更高版本，则无需费力地采取临时解决方法。
现在可以安全地修改前面给出的示例，如下所示。
public StreamedContent getImage() throws IOException {
FacesContext context = FacesContext.getCurrentInstance();
if (context.getCurrentPhaseId() == PhaseId.RENDER_RESPONSE) {
return new DefaultStreamedContent();
} else {
String id = context.getExternalContext().getRequestParameterMap().get("id");
byte[] bytes = Utils.isNumber(id) ? service.findImageById(Long.parseLong(id)) : null;
return bytes == null ? null : new DefaultStreamedContent(new ByteArrayInputStream(bytes));
}
}
在我厌倦了操纵/管理磁盘文件系统中存储的图像之后，我已经以BLOB(
LONGBLOB)的形式将图像移动到了数据库(MySQL)中。因此，我在
<p:dataTable>中显示图像，如下所示(从here:复制)。<p:column headerText="Header">
<p:graphicImage value="#{bannerBean.image}" height="200" width="200">
<f:param name="id" value="#{row.bannerId}"/>
</p:graphicImage>
<p:column>
检索图像的Bean如下。
@ManagedBean
@ApplicationScoped
public final class BannerBean
{
@EJB
private final BannerBeanLocal service=null;
public BannerBean() {}
public StreamedContent getImage() throws IOException {
FacesContext context = FacesContext.getCurrentInstance();
if (context.getCurrentPhaseId() == PhaseId.RENDER_RESPONSE) {
return new DefaultStreamedContent();
}
else {
String id = context.getExternalContext().getRequestParameterMap().get("id");
byte[] bytes = service.findImageById(Long.parseLong(id));
return bytes==null? new DefaultStreamedContent():new DefaultStreamedContent(new ByteArrayInputStream(bytes));
}
}
}
只要基础数据库表的每一行中都有图像，此方法就可以正常工作。
但是，在某些情况下，数据库中的BLOB类型列是可选的，因此，它也可以包含
null值。如果数据库中任何行中的此列为
null，则抛出以下异常。SEVERE: Error in streaming dynamic resource. null
WARNING: StandardWrapperValve[Faces Servlet]: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
at org.primefaces.application.PrimeResourceHandler.handleResourceRequest(PrimeResourceHandler.java:127)
at javax.faces.application.ResourceHandlerWrapper.handleResourceRequest(ResourceHandlerWrapper.java:153)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:643)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:344)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:70)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:316)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:722)
那么，如何管理
null BLOB以便该异常消失呢？返回
new DefaultStreamedContent(new ByteArrayInputStream(new byte[0]))，以防万一受管bean中的字节数组为null会抑制该异常，但这毕竟不是解决方案。这是理想的解决方案吗？在这种情况下，返回字节数组的EJB方法虽然完全没有必要。
public byte[] findImageById(Long id)
{
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<byte[]>criteriaQuery=criteriaBuilder.createQuery(byte[].class);
Root<BannerImages> root = criteriaQuery.from(BannerImages.class);
criteriaQuery.multiselect(root.get(BannerImages_.bannerImage));
ParameterExpression<Long>parameterExpression=criteriaBuilder.parameter(Long.class);
criteriaQuery.where(criteriaBuilder.equal(root.get(BannerImages_.bannerId), parameterExpression));
List<byte[]> list = entityManager.createQuery(criteriaQuery).setParameter(parameterExpression, id).getResultList();
return list!=null&&!list.isEmpty()?list.get(0):null;
}
最佳答案
这是 PrimeResourceHandler 中的错误(至少是功能/技术设计错误)。它不应该假定动态资源或其内容永远都不是null。它应该有条件地检查是否是这种情况，然后只需返回HTTP 404“未找到”响应。
换句话说，代替
85 streamedContent = (StreamedContent) ve.getValue(eLContext);
86
87 externalContext.setResponseStatus(200);
88 externalContext.setResponseContentType(streamedContent.getContentType());
他们应该做的
85 streamedContent = (StreamedContent) ve.getValue(eLContext);
86
87 if (streamedContent == null || streamedContent.getStream() == null) {
88 externalContext.responseSendError(HttpServletResponse.SC_NOT_FOUND, ((HttpServletRequest) externalContext.getRequest()).getRequestURI());
89 return;
90 }
91
92 externalContext.setResponseStatus(200);
93 externalContext.setResponseContentType(streamedContent.getContentType());
这样，您就可以从
null方法返回StreamedContent或空的getImage()来生成一个体面的404。好吧，你能做什么？
PrimeResourceHandler类的copy放在其自己的org.primefaces.application包中的webapp项目的Java源文件夹中，然后对其进行编辑以包括上述更改，最后像往常一样以WAR的方式构建/部署您的webapp项目。 /WEB-INF/classes中的类的加载优先级高于/WEB-INF/lib中JAR中的类的加载优先级，因此将改用经过修改的类。