【发布时间】：2012-07-11 14:09:27
【问题描述】：
我有一个 JSF 页面，我想在其中显示图像。图像作为 blob 存储在数据库中。 实体如下所示：
@Entity
public class Player
{
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
private Long id;
@Lob
private byte[] pictureData;
@Transient
private StreamedContent streamedPicture;
public StreamedContent getStreamedPicture()
{
if (streamedPicture == null && pictureData != null)
{
try
{
ByteArrayOutputStream os = new ByteArrayOutputStream();
os.write(pictureData);
streamedPicture = new DefaultStreamedContent(
new ByteArrayInputStream(
os.toByteArray()),
"image/png");
}
catch (FileNotFoundException e)
{}
catch (IOException e)
{}
}
return streamedPicture;
}
}
JSF 页面是这样的：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.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:ui="http://java.sun.com/jsf/facelets"
xmlns:p="http://primefaces.org/ui">
<h:head></h:head>
<body>
<ui:repeat var="player" value="#{playerbean.cachedPlayers}">
<h:outputText value="#{player.id}" />
<p:graphicImage value="#{player.streamedPicture}" rendered="#{player.streamedPicture != null}"/>
</ui:repeat>
</body>
</html>
我调用的 bean 看起来像这样：
@ManagedBean(name = "playerbean")
@SessionScoped
public class PlayerBean
implements Serializable
{
@EJB
private PlayerManager playerManager;
private List<Player> cachedPlayers;
public List<Player> getCachedPlayers()
{
if (cachedPlayers == null)
{
cachedPlayers = playerManager.getAll();
}
return cachedPlayers;
}
}
在调试时，我在方法handleResourceRequest() 中在PrimeResourceHandler 中设置了一个断点。我正在查看的PrimeResourceHandler 的代码包含以下内容：
try {
String dynamicContentEL = (String) session.get(dynamicContentId);
ELContext eLContext = context.getELContext();
ValueExpression ve = context.getApplication().getExpressionFactory().createValueExpression(context.getELContext(), dynamicContentEL, StreamedContent.class);
StreamedContent content = (StreamedContent) ve.getValue(eLContext);
HttpServletResponse response = (HttpServletResponse) context.getExternalContext().getResponse();
response.setContentType(content.getContentType());
byte[] buffer = new byte[2048];
int length;
InputStream inputStream = content.getStream();
while ((length = (inputStream.read(buffer))) >= 0) {
response.getOutputStream().write(buffer, 0, length);
}
response.setStatus(200);
response.getOutputStream().flush();
context.responseComplete();
} catch(Exception e) {
logger.log(Level.SEVERE, "Error in streaming dynamic resource.");
} finally {
session.remove(dynamicContentId);
}
当通过StreamedContent content = (StreamedContent) ve.getValue(eLContext); 行时，content 似乎为空。这当然会导致 NullPointerException。但是在 JSF 页面中，我告诉元素如果值为 null 则不要渲染。
【问题讨论】：
标签： jsf-2 primefaces