<p:graphicImage>不渲染图像
我有一个JSF页面，我想在其中显示一个图像。图像作为blob存储在数据库中。该实体如下所示：
@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页面如下所示：
<!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handleResourceRequest()方法的PrimeResourceHandler中设置了一个断点。我正在查看的PrimeResourceHandler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);
}当传递行时，StreamedContent content = (StreamedContent) ve.getValue(eLContext); content显示为null。这当然会导致NullPointerException。但是，在JSF页面中，我告诉元素，如果值为null，则不呈现该元素。
回答 1
Stack Overflow用户
发布于 2012-07-12 19:59:22
<p:graphicImage>组件不能具有指向SessionScoped bean中的托管属性的value属性。该值必须设置为RequestScoped bean。
这是因为image/jpeg内容类型HTTP响应的HTTP请求本质上是无状态的。浏览器将发出对JSF页面内容的初始请求，然后对于呈现的每个HTML标签，它将向每个<img>标签的动态生成的url发出单独的请求，以获取这些内容。在有状态上下文中获取图像没有实际意义。
https://stackoverflow.com/questions/11434517
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