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Gets a blob.
<satellite:blob [service="service name"] blobtable="blob table name" blobkey="primary key name" blobwhere="primary key value" blobcol="column_name" [blobheader="MIME type"] [classname="IReference class"] [outstring="output variable name"] [container="servlet|portlet"] [satellite="true|false"] [overridetype="export|dynamic"] [parentid="parent to log this blob as a dependency"] [csblobid="session variable"] [cachecontrol="expiration date and time"] [blobnocache="true|false"] [assembler="uri assembler short form"] [fragment="fragment value"] [scheme="scheme value"] [authority="authority value"] > <satellite:parameter name="ALT" value="alttext"/> <satellite:parameter name="BORDER" value="border_size"/> </satellite:blob>
service (optional)
service
to "img src"
. The default value is img src
. blobtable (required)
blobkey (required)
blobwhere (required)
blobcol (required)
blobheader (optional)
description
/extension
. For example, the MIME type for a GIF image is image/gif.classname (optional)
COM.FutureTense.Export.DiskPageRef
.outstring (optional)
container (optional)
servlet
or portlet
to construct a URL for that particular container. This is typically used as an override when constructing a link to a servlet from within a portlet. If this is omitted, Sites will detect the current container type and the current type will be used.satellite (optional)
true
or false
to force the url to be generated for a servlet context or a satellite server context respectively. If not specified (the default behaviour), Sites will detect whether or not the URL should be generated for Satellite Server and set the value accordingly.overridetype (optional)
export
can be specified to force a static link, and dynamic
can be specified to force a dynamic link.parentid (optional)
csblobid (optional)
img src
service parameter sends a new request to the application server after the browser reads the containing page. BlobServer then verifies if the csblobid
parameter was set. When BlobServer security is set to true and the csblobid
value matches the session variable value, the blob is served. If the values do not match a security violation is reported and no blob is served.cachecontrol (optional)
expiration
property to determine how long to cache this blob. You can override the default expiration value by specifying one of the following: never
- This blob should never expire for time reasons. Such objects are not guaranteed to stay in the cache forever. For example, if the cache is full, Sites-Satellite removes blobs on a LRU (Least Recently Used) basis. immediate
- Expire this blob immediately; in other words, to not cache this blob. expiration_date_and_time
- Specifies the precise date(s) and time(s) this blob should expire. blobnocache (optional)
true
prevents the blob and the header from being cached.assembler
(optional)fragment
(optional)http://www.myhost.com/foo.html#thirdParagraph
. scheme
(optional, required if authority is set)http
or https
. If this is left blank (and authority
is left blank) then the URL will be relative to the current scheme and authority. authority
(optional, required if scheme is set) scheme
. URLs are of the form scheme://authority/path?query#fragment
. For most purposes, authority corresponds to host:port
for the given application. Specifying scheme
and authority
allows for fully-qualified URLs to be created, which is useful for sites with multiple domains and in other cases.satellite:parameter (optional)
This tag retrieves a blob. satellite:blob
returns a link tag to render the link in the page.
This tag overrides the default caching expiration time defined by the Sites-Satellite expiration
property.
The satellite:blob
tag is the preferred method to render images, downloadable documents, and other large objects that are managed by Sites.
NoteThe |
Many Web sites contain images, such as banners or corporate logos, that never expire or seldom expire. Such images might appear on every page of content and be served millions of times per day. If a blob never expires (or seldom expires), your first impulse might be to use the satellite:blob
tag and set the cachecontrol
attribute to never
. This is an acceptable method of serving blobs, however, it does not provide the best performance. Whenever the cached blob is requested, Satellite must perform a lookup in the cache table. Each individual lookup does not require many resources, but Sites-Satellite might have to perform that same lookup millions of times per day.
An alternative way to serve never-expiring images is to do the following:
<img src="
pathname
">
HTML tags rather than through satellite:blob
Satellite JSP tags.
For example, consider a never-expiring corporate logo file named CorporateLogo.gif
. To use the alternate scheme, you first copy the file to the Web server's doc root on all your Sites-Satellite hosts. Then, instead of serving this logo through a satellite:blob
tag, your element could simply issue a tag like the following:
<img src="CorporateLogo.gif"/>
NoteBe careful when using this alternative mechanism for serving never-expiring images. For example, Sites-Satellite cannot warn you that one of the Sites-Satellite hosts does not contain the same image file as the other hosts. |
You can use the blobheadername
and blobheadervalue
arguments to specify http headers in the BlobServer response. For example, you can specify the content-type as follows:
blobheadername1="Content-Type" blobheadervalue1="image/gif"
If you want to use http headers to prevent browser caching of BlobServer requests for all browsers, use both HTTP 1.0 and HTTP 1.0 cache control directives. In the following example, the first header (Cache-Control:no-cache) is the HTTP 1.1 directive and the second header (Pragma:no-cache) is the HTTP 1.0 directive.
blobheadername1="Cache-Control" blobheadervalue1="no-cache" blobheadername2="Pragma" blobheadervalue2="no-cache"
To determine how long to cache the blob, these criteria are evaluated in this order:
cachecontrol
attribute.cachecontrol
, the value in the satellite.blob.cachecontrol.default
property, found in the futuretense.ini
property file, is used.satellite.blob.cachecontrol.default
, the value of the expiration
property, located in the satellite.properties
property file, is used. We recommend that you set values for the satellite.blob.cachecontrol.default
properties that make sense for the majority of your blobs. If you want to override the default expiration time, use the cachecontrol
parameter.
<satellite:blob service="img src" blobtable="MyImageTable" blobkey="id" blobwhere="12345" blobcol="urlpicture" blobheader="image/gif" cachecontrol="*:30:0 */*/*"> <satellite:parameter name='ALT' value='imagelist.alttext'/> <satellite:parameter name='BORDER' value='0'/> </satellite:blob>
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Oracle JSP Tag Reference |