< p:graphicImage>不渲染图像 [英] <p:graphicImage> not rendering image
问题描述
我有一个要显示图像的JSF页面.图像作为斑点存储在数据库中. 实体看起来像这样:
I have a JSF page where I want to show a image. The image is stored in the database as a blob. The entity looks like this:
@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:
The JSF page is this:
<!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:
And the bean I call looks like this:
@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()中的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:
While debugging I set a breakpoint in PrimeResourceHandler in the method handleResourceRequest(). The code of the PrimeResourceHandler I'm looking at contains this:
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);
}
通过时，行StreamedContent content = (StreamedContent) ve.getValue(eLContext); content似乎为空.当然，这会导致NullPointerException.但是，在JSF页面中，我告诉元素如果值为null则不要渲染.
When passing the line StreamedContent content = (StreamedContent) ve.getValue(eLContext); content appears to be null. This of course causes a NullPointerException. However in the JSF page I told the element not to render if the value is null.
推荐答案
<p:graphicImage>组件不能具有指向SessionScoped bean中托管属性的value属性.该值必须设置为RequestScoped bean.
The <p:graphicImage> component cannot have a value attribute that points to a managed property within a SessionScoped bean. The value must be set to a RequestScoped bean.
这是因为对image/jpeg内容类型HTTP响应的HTTP请求本质上是无状态的.浏览器将对JSF页面内容进行初始请求，然后对于呈现的每个HTML <img>标签，它将分别对每个<img>标签的动态生成的URL进行单独的请求以获取这些内容.在有状态的上下文中获取图像实际上没有任何意义.
This is because an HTTP request for an image/jpeg content type HTTP response is inherently stateless. The browser will make the initial request for the JSF page content, then for every HTML <img> tag that is rendered it will make seperate requests to the dynamically generated url of each <img> tag to fetch these. Fetching an image in a stateful context doesn't really make sense.
这篇关于< p:graphicImage>不渲染图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
