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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"]
    [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"]
>
    <satellite:parameter name="ALT" value="alttext"/>
<satellite:parameter name="BORDER" value="border_size"/>
</satellite:blob>

Parameters

service (required)

Specify the start of the HTML tag to hold this blob. For example, if the blob is an image, set service_name to "img 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 (required)

MIME type for returned data. It takes the form description/extension. For example, the MIME type for a GIF image is image/gif.

parentid (optional)

The id against which this blob should be logged as a dependency.

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 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)

Specifies when this blob expires from the cache. If you omit this tag, CS-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, CS-Satellite removes blobs on a LRU (Least Recently Used) basis.
• immediate - Expire this blob immediately; in other words, to not cache this page.
• expiration_date_and_time - Specifies the precise date(s) and time(s) this blob should expire.
• session:expiration_date_and_time - Specifies the precise date(s) and time(s) this blob should expire. Placing the word session in front of expiration_date_and_time tells CS-Satellite to serve this blob only to the person who originally requested it.

blobnocache (optional)

Whether or not to disable blob caching. A value of true prevents the blob from being cached.

assembler (optional)

Short form name for uri assembler class. Specifying an assembler overrides the default assembler used by Content Server to construct URLs. Omitting this value will cause URLs generated by this tag to use the assembler registered with an index of 0 in the request property file.

 

ALT (optional)

Alternate text associated with the blob.

BORDER (optional)

Sets the border size for the blob.

Description

This tag retrieves a blob. If the specified blob is already cached on this CS-Satellite, satellite:blob loads it into the page. If the specified blob is not already cached on this CS-Satellite, satellite:blob extracts the blob from a table, caches it, and loads it into the page. Keep in mind that this tag works regardless of the cookie setting on the browser.

This tag overrides the default caching expiration time defined by the CS-Satellite expiration property.

The satellite:blob tag is the preferred method to render images, downloadable documents, and other large objects that are managed by Content Server.

Note The satellite:blob tag functions correctly 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 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 CS-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 CS-Satellite hosts. Place them under the doc root for the Web server.

• Access them through <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 CS-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">

Note Be careful when using this alternative mechanism for serving never-expiring images. For example, CS-Satellite cannot warn you that one of the CS-Satellite hosts does not contain the same image file as the other hosts.

You can use the blobheadername and blobheadervalue parameters 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 a page or pagelet, these criteria are evaluated in this order:

1. A value passed in using the cachecontrol parameter.

2. If there is no value in cachecontrol, the value in the satellite.page.cachecontrol.default property, found in the futuretense.ini property file, is used.

3. If there is no value in satellite.page.cachecontrol.default, the value of the expiration property, located in the satellite.ini property file, is used.

We recommend that you set values for the satellite.page.cachecontrol.default properties that make sense for the majority of your pages and pagelets.  If you want to override the default expiration time, use the cachecontrol parameter.  Use the expiration property to determine the timeout for pages that are not generated from this tag; for example, pages that are generated directly from a URL.

Example

<%   
StringBuffer bf = new StringBuffer()

ics.SetVar("category", "logo")

IList list = ics.SelectTo("MyImageTable", 
        "id,urlpicture,alttext",
        "category", 
         null, 
        1, 
        "imagelist", 
         true, 
        bf)
%>

<satellite:blob>
    <satellite:parameter name='service' value='img src'/>
    <satellite:parameter name='blobtable' value='MyImageTable'/>
    <satellite:parameter name='blobkey' value='id'/>
    <satellite:parameter name='blobwhere' value='imagelist.id'/>
    <satellite:parameter name='blobcol' value='urlpicture'/>
    <satellite:parameter name='blobheader' value='image/gif'/>
    <satellite:parameter name='cachecontrol' value='*:30:0 */*/*'/>
    <satellite:parameter name='ALT' value='imagelist.alttext'/>
    <satellite:parameter name='BORDER' value='0'/>
</satellite:blob>

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	FatWire JSP Tag Reference Copyright 2005 by FatWire Software All rights reserved.