sunlabs.brazil.filter
public class FilterHandler extends Object implements Handler
FilterHandler
captures the output of another
Handler
and allows the ouput to
be modified. One or more
{@link sunlabs.brazil.filter.Filter Filters}
may be specified to change that output
before it is returned to the client.
This handler provides one of the core services now associated with the Brazil Server: the ability to dynamically rewrite web content obtained from an arbitrary source.
For instance, the FilterHandler
can be used as a proxy for
a PDA. The wrapped Handler
would go to the web to
obtain the requested pages on behalf of the PDA. Then, a
Filter
would examine all "text/html" pages and rewrite the
pages so they fit into the PDA's 200 pixel wide screen. Another
Filter
would examine all requested images and dynamically
dither them to reduce the wireless bandwidth consumed by the PDA.
The following configuration parameters are used to initialize this
Handler
:
handler
Handler
whose output will be captured
and then filtered. This is called the "wrapped handler".
filters
Filter
names. The filters are applied in
the specified order to the output of the wrapped handler.
exitOnError
initFailure
will set
any of the filters fail to
initialize. No handler prefix is required.
handler=filter port=8081 filter.class=sunlabs.brazil.filter.FilterHandler filter.handler=proxy filter.filters=noimg proxy.class=sunlabs.brazil.proxy.ProxyHandler noimg.class=sunlabs.brazil.filter.TemplateFilter noimg.template=sunlabs.brazil.template.NoImageTemplateThese parameters set up a proxy server running on port 8081. As with a normal proxy, this proxy server forwards all HTTP requests to the target machine, but it then examines all HTML pages before they are returned to the client and strips out all
<img>
tags. By applying
different filters, the developer could instead build a server Version: 2.3
Field Summary | |
---|---|
Filter[] | filters |
Handler | handler |
Method Summary | |
---|---|
boolean | init(Server server, String prefix)
Start the handler and filter classes. |
boolean | respond(Request request)
Responds to an HTTP request by the forwarding the request to the
wrapped Handler and filtering the output of that
Handler before sending the output to the client.
|
Handler
and filtering the output of that
Handler
before sending the output to the client.
At several stages, the Filters
are given a chance to
short-circuit this process:
Filter
is given a chance to examine the
request before it is sent to the Handler
by invoking its respond() method. The
Filter
may decide to change the request's properties.
A Filter
may even return some content to the client now,
by (calling request.sendResponse()
and
returning true),
in which case, neither the Handler
nor any further
Filter
s are invoked at all.
handler's respond()
method is called, and is expected to generate content.
If no content is generated at this step,
this handler returns false.
Handler
has generated the response headers,
but before it has generated any content, each Filter
is
asked if it would be interested in filtering the content. If no
Filter
is, then the subsequent content from the
Handler
will be sent directly to the client.
Filter
is interested
in filtering the content, then the output of the Handler
will be sent to each of the interested Filter
s in order.
The output of each interested Filter
is sent to the
next one; the output of the final Filter
is sent to
the client.
Filter
s
can decide to reject the content completely, instead of rewriting it.
Parameters: request The HTTP request to be forwarded to one of the sub-servers.
Returns: true
if the request was handled and content
was generated, false
otherwise.
Throws: IOException if there was an I/O error while sending the response to the client.