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satellite:blob
Gets a blob.
Syntax
<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>Attributes
service (optional)
- Specify the start of the HTML tag to hold this blob. For example, if the blob is an image, set
service
to"img src"
. The default value isimg src
.blobtable (required)
- Name of the content table containing the binary data.
blobkey (required)
- Name of the column used as the table's primary key.
blobwhere (required)
- Value of the primary key for the row containing the binary data.
blobcol (required)
- Name of the column containing the binary data.
blobheader (optional)
- MIME type for returned data. It takes the form
description
/extension
. For example, the MIME type for a GIF image is image/gif.classname (optional)
- Input. This parameter is used by the URL generation mechanism to allow the class implementing the IReference interface to be overidden. This can be useful when modifying the URL structure or when modifying the exported path names. The default value is
COM.FutureTense.Export.DiskPageRef
.outstring (optional)
- The name of the output variable containing the URL to blob.
container (optional)
- Input. Specify either
servlet
orportlet
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)
- Specify either
true
orfalse
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)
- This parameter is used by the URL generation mechanism to override the type of link to be generated. By default, Sites will generate a dynamic link if the page is being generated dynamically, and a static link if the page is being exported.
export
can be specified to force a static link, anddynamic
can be specified to force a dynamic link.parentid (optional)
- The id against which this blob should be logged as a dependency. When a blob is cached, an item dependency can be recorded against the cache key to provide a content-based identifier for accessing the cached blob, rather than requiring the cache key to do so. This is useful in cache management. When coupled with an asset identifier, this can allow blobs to be flushed when an asset is updated.
csblobid (optional)
- The value of this parameter must correspond to a session variable of the same name when BlobServer security is on. When a request is made to the BlobServer, the
img src
service parameter sends a new request to the application server after the browser reads the containing page. BlobServer then verifies if thecsblobid
parameter was set. When BlobServer security is set to true and thecsblobid
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)
- Specifies when this blob expires from the cache. If you omit this tag, Sites-Satellite uses the value of the
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)
- Whether or not to disable blob caching. A value of
true
prevents the blob and the header from being cached.assembler
(optional)- Short form name for uri assembler class. Specifying an assembler overrides the default assembler used by Sites to construct URLs. Omitting this value will cause URLs generated by this tag to use the assembler registered with the highest priority in the request property file.
fragment
(optional)- Optional attribute to specify a fragment on the URL. Fragments, sometimes known as anchors, allow browsers to advance to a specific location in a single web page. ex.
http://www.myhost.com/foo.html#thirdParagraph
.scheme
(optional, required if authority is set)- Attribute that allows the scheme to be set in the URL. The scheme in the case of most URLs refers to the protocol and is usually set to either
http
orhttps
. If this is left blank (andauthority
is left blank) then the URL will be relative to the current scheme and authority.authority
(optional, required if scheme is set)- Attribute that allows the user to specify a fully-qualified URL, when used in conjunction with
scheme
. URLs are of the formscheme://authority/path?query#fragment
. For most purposes, authority corresponds tohost:port
for the given application. Specifyingscheme
andauthority
allows for fully-qualified URLs to be created, which is useful for sites with multiple domains and in other cases.Arguments
satellite:parameter (optional)
- Arbitrary name-value pair that is added to the URL.
Description
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.
Note
The
satellite:blob
tag functions correctly even when cookies are disabled.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 thecachecontrol
attribute tonever
. 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:
- Copy the never-expiring images to all your Sites-Satellite hosts. Place them under the doc root for the Web server.
- Access them through
<img src="
pathname
">
HTML tags rather than throughsatellite: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 asatellite:blob
tag, your element could simply issue a tag like the following:<img src="CorporateLogo.gif"/>
Note
Be 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
andblobheadervalue
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:
- A value passed in using the
cachecontrol
attribute.- If there is no value in
cachecontrol
, the value in thesatellite.blob.cachecontrol.default
property, found in thefuturetense.ini
property file, is used.- If there is no value in
satellite.blob.cachecontrol.default
, the value of theexpiration
property, located in thesatellite.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 thecachecontrol
parameter.Example
<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
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