BgImageServlet (DHD Multimedia Gallery V1.53.0 Javadoc)

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org.hd.d.pg2k.webSvr.bgImg
Class BgImageServlet

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
          org.hd.d.pg2k.webSvr.bgImg.BgImageServlet

All Implemented Interfaces:: java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public final class BgImageServlet
extends javax.servlet.http.HttpServlet
extends javax.servlet.http.HttpServlet

Servlet to serve dynamic and partially-random HTML-page background image. This serves a randomly-generated image which we would like to be slightly different for each visitor.

This is intended to be pleasing on the eye, and possible, if required, to read normal black text over. So the image is nearly white with a slowly changing 'watermark' image.

To minimise bandwidth fetching this, and CPU time generating it, this is designed to be served with the "caching" filter in front of it, so that any one user should typically only fetch a new image once per week or thereabouts, though each user should get a different one. Also, the image dimensions and quality are adjusted to those of a "standard" thumbnail, which does not take you lots of space in memory or on the wire.

We may cache the last image generated, so that if the system is busy the last image may be returned again rather than a new one being generated.

See Also:: Serialized Form

Field Summary
`private static byte[][]`	`_imageCache` Simple cache by "seed" value of background images as raw byte[]; each entry is computed on demand.
`private static java.lang.Object`	`_imageCacheLock` Lock for access to _imageCache.
`private static long`	`creationTime` Construction time for this class.
`private static int`	`MIN_BGS` Minimum number of different backgrounds seen; strictly positive.
`private static long`	`serialVersionUID` Unique Serialisation class ID generated by http://random.hd.org/.

Constructor Summary
`BgImageServlet()`

Method Summary
`void`	`doAction(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Respond to a GET/HEAD request for the content served by this servlet.
`void`	`doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Respond to a GET request for the content served by this servlet.
`void`	`doHead(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Respond to a HEAD request for the content served by this servlet.

Methods inherited from class javax.servlet.http.HttpServlet
`doDelete, doOptions, doPost, doPut, doTrace, getLastModified, service, service`

Methods inherited from class javax.servlet.GenericServlet
`destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, init, log, log`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

creationTime

private static final long creationTime

Construction time for this class. Used to modify the relationship between client IP address and the background selected.

MIN_BGS

private static final int MIN_BGS

Minimum number of different backgrounds seen; strictly positive. Possibly good if prime to scatter client's more uniformly across the image set.

As this value gets larger, memory consumption will go up.

We set this not to use more than about 1%--2% of total memory, although we may find an abnormally-small heap size during startup when this will get computed.

_imageCache

private static final byte[][] _imageCache

Simple cache by "seed" value of background images as raw byte[]; each entry is computed on demand. This is indexed by a hash on the client's IP address, and caches a background image.

The size of this array determines how many different images we hold, and more will use more memory.

Access the array contents only under the _imageCacheLock.

We vary the size of this array a little on each run to vary the mix. The array size stays constant while the class remains loaded.

_imageCacheLock

private static final java.lang.Object _imageCacheLock

Lock for access to _imageCache.

serialVersionUID

private static final long serialVersionUID

Unique Serialisation class ID generated by http://random.hd.org/.

See Also:: Constant Field Values

Constructor Detail

BgImageServlet

public BgImageServlet()

Method Detail

doGet

public void doGet(javax.servlet.http.HttpServletRequest request,
                  javax.servlet.http.HttpServletResponse response)
           throws java.io.IOException

Respond to a GET request for the content served by this servlet.

Overrides:: doGet in class javax.servlet.http.HttpServlet

Parameters:: request - The servlet request we are processing; response - The servlet response we are producing
Throws:: java.io.IOException - if an input/output error occurs

doHead

public void doHead(javax.servlet.http.HttpServletRequest request,
                   javax.servlet.http.HttpServletResponse response)
            throws java.io.IOException

Respond to a HEAD request for the content served by this servlet.

Overrides:: doHead in class javax.servlet.http.HttpServlet

Parameters:: request - The servlet request we are processing; response - The servlet response we are producing
Throws:: java.io.IOException - if an input/output error occurs

doAction

public void doAction(javax.servlet.http.HttpServletRequest request,
                     javax.servlet.http.HttpServletResponse response)
              throws java.io.IOException

Respond to a GET/HEAD request for the content served by this servlet. Returns the exhibit data, with a correct MIME type.

Parameters:: request - The servlet request we are processing; response - The servlet response we are producing
Throws:: java.io.IOException - if an input/output error occurs