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screen scrape

 
 
plork123
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      09-29-2005
hi all ,

can anyone give me an example of screen scraping a website and return
the result e.g. html as a string

or lead me to some tutorials / examples

many thanks

 
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Oliver Wong
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      09-29-2005

"plork123" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> hi all ,
>
> can anyone give me an example of screen scraping a website and return
> the result e.g. html as a string
>
> or lead me to some tutorials / examples


Typically, for websites, you don't need to do screen scrapping. It's
much easier to just parse the HTML data.

- Oliver


 
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Roedy Green
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      09-29-2005
On 29 Sep 2005 09:30:09 -0700, "plork123" <(E-Mail Removed)> wrote
or quoted :

>can anyone give me an example of screen scraping a website and return
>the result e.g. html as a string

Here is a rough and ready screen scraper I wrote to pluck exchange
rates off the Oanda site. They siced the legal people on me so I had
to quickly desist using it. However, you could use it as a model.

This is not beautiful code. It is just to show proof of concept. It
uses unnecessarily low-level socket code. It was easier at the time
that trying to decipher how Sun's classes worked.

I offer this as is.

/* Oanda complained, so I had to discontinue this.
* Requests a currency conversion from Oanda.com
* I pretend to be a browser, get the page and extract the part I
want.
* copyright (c) 1998-2005 Roedy Green, Canadian Mind Products
* #327 - 964 Heywood Avenue
* Victoria, BC Canada V8V 2Y5
* tel: (250) 361-9093
* mailto(E-Mail Removed)
* http://mindprod.com
*/
package com.mindprod.currcon;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import com.mindprod.voter.CGIRequest;
import com.mindprod.voter.CGIget;

public class Oanda
{
/**
* undisplayed copyright notice
*/
private static final String EmbeddedCopyright =
"copyright (c) 2003-2005 Roedy Green, Canadian Mind Products,
http://mindprod.com";

// c o n f i g u r a t i o n s t r i n g s

/**
* Site URL to process the cgi script. without http:// on front
*/
final static String host = "www.oanda.com";

/**
* Name of CGI Script to process this vote, namely the ACTION
parameter, without host.
* absolute name on host.
*/
final static String relativeURL = "/convert/fxdaily";

/**
* get list of currencies to fetch, and glue them together
separated with underscores.
*
* @return String of currency codes wanted, separated
* by underscores. e.g. CAD_USD_EUR
*/
public static String getWantedCurrencies () throws IOException
{
BufferedReader r = new BufferedReader ( new FileReader (
"oanda.wanted" ), 4096 );
StringBuffer sb = new StringBuffer ( 700 );
String line;
while ( ( line = r.readLine () ) != null )
{
sb.append ( "_" );
sb.append ( line );
}
return sb.toString().substring( 1 );
}

/**
* extract the useful CSV info out of the web page.
*
* @param haystack the entire webpage
* @return Extracted goodies, just the CSV data.
*/
static String extractGoodies ( String haystack )
{
/* Result that comes back in embedded a large web page.
We find it by
<PRE><font face=Verdana size=2>Currency,Code,USD/1 Unit,Units/1
USD

Canadian Dollar,CAD,0.7283,1.3737
Swiss Franc,CHF,0.7739,1.2933
British Pound,GBP,1.6325,0.6127
Japanese Yen,JPY,0.008562,116.9
</TD></TR></font></PRE>
*/
String lookFor = "<PRE><font face=Verdana
size=2>Currency,Code,USD/1 Unit,Units/1 USD";
int startGoodies = haystack.indexOf( lookFor );
if ( startGoodies < 0 )
{
System.out.println("failure. Oanda format change.");
System.exit(1);
return null;
}
else
{
// bypass junk on front
haystack = haystack.substring( startGoodies +
lookFor.length() + 2 );
int endGoodies = haystack.indexOf( "</TD>" );
if ( endGoodies < 0 )
{
System.out.println("failure. Oanda format change.");
System.exit(1);
return null;
}
return haystack.substring( 0, endGoodies );
}
}

/**
* Save the results in the oanda.csv file.
*
* @param result Results to save, in csv format.
*
* @exception IOException
*/
static void save ( String result ) throws IOException
{
// save result in oand.csv ready for further processing.
FileWriter w = new FileWriter ( "oanda.csv" );
w.write( result );
w.close();
}
/**
* Connect and send request
*/
public static void main (String[] args)
{
try
{
String currencies = getWantedCurrencies();

// prepare http parms to server and get return data
CGIRequest p = new CGIRequest( 2000 );
// order appears to matter.
p.appendCGIPair( "value", "1" );
// leave out date to get today's date.
p.appendCGIPair( "date_fmt", "jp" );
p.appendCGIPair( "redirected", "1" );
p.appendCGIPair( "result", "1" );
p.appendCGIPair( "lang", "en" );
p.appendCGIPair( "exch", "USD" );
p.appendCGIPair( "exch2", "" );
p.appendCGIPair( "expr2", "" );
p.appendCGIPair( "format", "CSV" );
p.appendCGIPair( "dest", "Get Table" );
p.appendCGIPair( "sel_list", currencies );
String parms = p.toString();

System.out.println( "sending request to oanda.com. Please be
patient." );

// ask oanda for exchange rates on given list of currencies.
String haystack = CGIget.get( host, relativeURL, parms );

/* extract good stuff from the whole web page */
String result = extractGoodies ( haystack );

System.out.println( result );

save ( result );
}
catch ( IOException e )
{
System.out.println(e);
}
} // end class Main
} // end class Oanda


package com.mindprod.voter;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;

/**
* Like A StringBuffer but encodes CGI pairs.
*
* @author Roedy Green
* @version 1.0
* @since 2003-05-26
*/
public class CGIRequest
{
// ideally would extend StringBuffer, but it is final.

/**
* constructor
*
* @param size estimated size of result string.
*/
public CGIRequest ( int size )
{
this.sb = new StringBuffer (size);
}

private final StringBuffer sb;

/**
* append a parm=value pair of CGI parameters,
* ecoding them with URL encoding, xxx=yyy&aaa=bbb etc.
*
* @param name parameter name
*
* @param value parameter value
*/
public void appendCGIPair ( String name, String value )
{
if ( sb.length() != 0 )
{
// separates pairs
sb.append( '&' );
}
try
{
sb.append( URLEncoder.encode( name , "ASCII" ) );
sb.append ( '=' );
sb.append( URLEncoder.encode( value, "ASCII" ) );
}
catch ( UnsupportedEncodingException e )
{
throw new IllegalArgumentException("ASCII encoding support
missing");
}

}

/**
* get request as an a URL-encoded String.
*
* @return result CGI request string.
*/
public String toString()
{
return sb.toString();
}
}

// Class com/mindprod/voter/CGIpost.java
// copyright (c) 1998-2005 Roedy Green, Canadian Mind Products
// based on work by Jonathan Revusky

// To encode strings use java.net.URLEncoder.encode;
// and Java.net.URLDecoder.decode or CGIRequest.

/*
* copyright (c) 1998-2005
* Roedy Green
* Canadian Mind Products
* #327 - 964 Heywood Avenue
* Victoria, BC Canada V8V 2Y5
* tel: (250) 361-9093
* mailto(E-Mail Removed)
* http://mindprod.com
*/
// Version 1.0

package com.mindprod.voter;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.Socket;
import java.net.URL;

/**
* simulates a browser posting a form to CGI via POST.
*/
public class CGIpost
{
/**
* Static only. Prevent instantiation.
*/
private CGIpost()
{
}
/**
* Send a formful of data to the CGI host using POST
*
* @param websiteURL URL of the website
* @param relativeURL
* relative URL of the document/CGI desired
* Absolute begin with /.
*
* @param parms parms to send, encoded with URLEncoder
*
* @return CGI host's response with headers and embedded length
fields stripped
* @exception IOException
*/
public static String post( String websiteURL, String relativeURL,
String parms ) throws IOException
{
// O P E N

URL url = new URL ( "http://" + websiteURL + '/' + relativeURL
);
HttpURLConnection urlc =
(HttpURLConnection)url.openConnection();
urlc.setAllowUserInteraction( false );
urlc.setDoInput( true );
urlc.setDoOutput( true );
urlc.setUseCaches( false );
urlc.setRequestMethod( "POST" );
// could set Referer: here
urlc.setRequestProperty( "Content-length", ( Integer.toString(
parms.length() ) ) );

urlc.connect();
InputStream is = urlc.getInputStream();

OutputStream os = urlc.getOutputStream();
// parms are the data content.
os.write( parms.getBytes( "8859_1" /* encoding */ ) );
os.close();

int statusCode;
statusCode = urlc.getResponseCode();
// get size of message. -1 means comes in an indeterminate
number of chunks.
int estimatedLength = (int)urlc.getContentLength();
if ( estimatedLength < 0 )
{
estimatedLength = 32*1024;
}

// R E A D
String result = CGIget.readEverything( is, estimatedLength );
// C L O S E
is.close();
urlc.disconnect();

return result;
} // end get



/**
* Send a formful of data to the CGI host using POST.
* @param websiteURL URL of the website
* @param relativeURL
* relative URL of the document/CGI desired
* Absolute begin with /.
*
* @return CGI host's response, including headers and length
fields.
*/
public static String rawPost( String websiteURL, String
relativeURL, String parms ) throws IOException

{
URL url = new URL( "http://" + websiteURL );
int port = url.getPort();
if ( port == -1 ) port = 80;

Socket sock = new Socket( websiteURL, port );


// Obtain data streams
OutputStream os = sock.getOutputStream();
InputStream is = sock.getInputStream();

StringBuffer sb = new StringBuffer( 1000 );
sb.append( "POST" );
sb.append( " " );
sb.append( relativeURL );
sb.append( "HTTP/1.1\n" );
sb.append( " " );
sb.append( "User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;
Windows NT 5.0) Opera 7.11 [en]\n" );

sb.append( "Host: " );
sb.append( websiteURL );
sb.append( "\n" );

sb.append( "Accept: text/html, image/png, image/jpeg, image/gif,
image/x-xbitmap, */*;q=0.1\n" );
sb.append( "Accept-Language: en\n" );
sb.append( "Accept-Charset: windows-1252, utf-8, utf-16,
iso-8859-1;q=0.6, *;q=0.1\n" );
sb.append( "Accept-Encoding: deflate, gzip, x-gzip, identity,
*;q=0\n" );

// Referer: could go here
// cookies would go here.


sb.append( "Connection: Keep-Alive, TE\n" );
sb.append( "TE: deflate, gzip, chunked, identity, trailers\n" );
sb.append( "Content-type: application/x-www-form-urlencoded\n"
);

sb.append( "Content-Length: " );
sb.append( parms.length() );
sb.append( "\n\n" );


String header = sb.toString();

os.write( header.getBytes( "8859_1" /* encoding */ ) );
os.write( parms.getBytes( "8859_1" /* encoding */ ) );
os.close();

// Read data FROM server till -1 eof
String result = CGIget.readEverything ( is, 32*1024 );

is.close();
return result;
} // end post

} // end class CGIPost

// Class com/mindprod/voter/CGIget.java
// copyright (c) 1998-2005 Roedy Green, Canadian Mind Products
// based on work by Jonathan Revusky

// To encode strings use java.net.URLEncoder.encode;
// and Java.net.URLDecoder.decode or CGIRequest.
/*
* copyright (c) 1998-2005
* Roedy Green
* Canadian Mind Products
* #327 - 964 Heywood Avenue
* Victoria, BC Canada V8V 2Y5
* tel: (250) 361-9093
* mailto(E-Mail Removed)
* http://mindprod.com
*/
// Version 1.0

package com.mindprod.voter;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.Socket;
import java.net.URL;

/**
* simulates a browser posting a form to CGI via GET.
*/
public class CGIget
{
/**
* Static only. Prevent instantiation.
*/
private CGIget()
{
}
/**
* Send a formful of data to the CGI host using GET.
*
* @param websiteURL URL of the website
* @param relativeURL
* relative URL of the document/CGI desired
* Absolute begin with /.
*
* @param parms parms to send, encoded with URLEncoder
*
* @return CGI host's response with headers and embedded length
fields stripped
* @exception IOException
*/
public static String get( String websiteURL, String relativeURL,
String parms ) throws IOException
{
// O P E N

URL url = new URL ( "http://" + websiteURL + '/' + relativeURL +
'?' + parms );
HttpURLConnection urlc =
(HttpURLConnection)url.openConnection();
urlc.setAllowUserInteraction( false );
urlc.setDoInput( true );
urlc.setDoOutput( false );
urlc.setUseCaches( false );
urlc.setRequestMethod( "GET" );
urlc.connect();
InputStream is = urlc.getInputStream();

int statusCode;
statusCode = urlc.getResponseCode();
// get size of message. -1 means comes in an indeterminate
number of chunks.
int estimatedLength = (int)urlc.getContentLength();
if ( estimatedLength < 0 )
{
estimatedLength = 32*1024;
}

// R E A D
String result = readEverything( is, estimatedLength );
// C L O S E
is.close();
urlc.disconnect();

return result;
} // end get



/**
* Send a formful of data to the CGI host using GET.
*
* @param websiteURL URL of the website
* @param relativeURL
* relative URL of the document/CGI desired
* Absolute begin with /.
* @param parms parms to send, encoded with URLEncoder
* @return CGI host's response, raw, everything incuding headers
and embedded length fields
* @exception IOException
*/
public static String getRaw( String websiteURL, String relativeURL,
String parms ) throws IOException
{

URL url = new URL( "http://" + websiteURL );
int port = url.getPort();
if ( port == -1 ) port = 80;
Socket sock = new Socket( websiteURL, port );

// Obtain data streams
OutputStream os = sock.getOutputStream();
InputStream is = sock.getInputStream();


StringBuffer sb = new StringBuffer( 1000 );
sb.append( "GET" );
sb.append( " " );
sb.append( relativeURL );

if ( parms.length() > 0 )
{
sb.append( "?");
sb.append( parms );
}

sb.append( " " );
sb.append( "HTTP/1.1\n" );
sb.append( "User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;
Windows NT 5.0) Opera 7.11 [en]\n" );

sb.append( "Host: " );
sb.append( websiteURL );
sb.append( "\n" );

sb.append( "Accept: text/html, image/png, image/jpeg, image/gif,
image/x-xbitmap, */*;q=0.1\n" );
sb.append( "Accept-Language: en\n" );
sb.append( "Accept-Charset: windows-1252, utf-8, utf-16,
iso-8859-1;q=0.6, *;q=0.1\n" );
sb.append( "Accept-Encoding: deflate, gzip, x-gzip, identity,
*;q=0\n" );

// Referer: could go here.
// cookies could go here.

sb.append( "Connection: Keep-Alive, TE\n" );
sb.append( "TE: deflate, gzip, chunked, identity, trailers\n" );
sb.append( "Content-type: application/x-www-form-urlencoded\n"
);
sb.append( "\n" );

String header = sb.toString();

os.write( header.getBytes( "8859_1" /* encoding */ ) );
os.close();

// Read data FROM server till -1 eof
// get everything. headers, embedded length counts etc.
String result = readEverything ( is, 32*1024 );

is.close();
return result;
} // end getRaw

/**
* Used to read until EOF on an Inputstream that
* sometimes returns 0 bytes because data have
* not arrived yet. Does not close the stream.
*
* @param is InputStream to read from.
* @param estimatedLength
* Estimated number of bytes that will be read.
* -1 or 0 mean you have no idea. Best to make
* some sort of guess a little on the high side.
* @return String representing the contents of the entire
* stream.
*/
public static String readEverything( InputStream is, int
estimatedLength ) throws IOException
{
if ( estimatedLength <= 0 )
{
estimatedLength = 10*1024;
}

StringBuffer buf = new StringBuffer( estimatedLength );

int chunkSize = Math.min ( estimatedLength, 4*1024 );
byte[] ba = new byte[ chunkSize ];

// -1 means eof, 0 means none available for now.
int bytesRead;

while ( ( bytesRead = is.read( ba, 0, chunkSize )) >= 0 )
{
if ( bytesRead == 0 )
{
try
{
// no data for now
// wait a while before trying again to see if data has
arrived.
// avoid hogging cpu in a tight loop
Thread.sleep( 100 );
}
catch ( InterruptedException e )
{
Thread.currentThread().interrupt();
}
}
else
{
// got some data
buf.append( new String( ba, 0, bytesRead , "8859_1" /*
encoding */) );
}
}
return buf.toString();
} // end readEverything

/**
* Reads exactly len bytes from the input stream
* into the byte array. This method reads repeatedly from the
* underlying stream until all the bytes are read.
* InputStream.read is often documented to block like this, but in
actuality it
* does not always do so, and returns early with just a few bytes.
* readBlocking blocks until all the bytes are read,
* the end of the stream is detected,
* or an exception is thrown. You will always get as many bytes as
you
* asked for unless you get an eof or other exception.
* Unlike readFully, you find out how many bytes you did get.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data in the array,
* not offset into the file!
* @param len the number of bytes to read.
* @return number of bytes actually read.
* @exception IOException if an I/O error occurs.
*
*/
public static final int readBlocking ( InputStream in , byte b[ ],
int off, int len ) throws IOException
{
int totalBytesRead = 0;
while ( totalBytesRead < len )
{
int bytesRead = in.read( b , off + totalBytesRead , len -
totalBytesRead );
if ( bytesRead < 0 )
{
break;
}
if ( bytesRead == 0 )
{
try
{
// no data for now
// wait a while before trying again to see if data has
arrived.
// avoid hogging cpu in a tight loop
Thread.sleep( 100 );
}
catch ( InterruptedException e )
{
Thread.currentThread().interrupt();
}
}
else
{
totalBytesRead += bytesRead;
}
}
return totalBytesRead;
}
// end readBlocking

} // end class CGIget
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.
 
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Roedy Green
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Posts: n/a
 
      09-29-2005
On Thu, 29 Sep 2005 21:23:39 GMT, "Oliver Wong" <(E-Mail Removed)>
wrote or quoted :

> Typically, for websites, you don't need to do screen scrapping. It's
>much easier to just parse the HTML data.


I think the term come to be used more generically than the original
literal meaning of grabbing chars out of the regen buffer. When
people say screen scraping today what they mean is extracting data
from web pages designed for humans to read.
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.
 
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plork123
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      09-30-2005
Thanks very much for your help, much appreicated

 
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plork123
Guest
Posts: n/a
 
      09-30-2005
Thanks for your reply
> It's much easier to just parse the HTML data.


Do you have an example/tutorial of how this is done?

Many thanks

 
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Oliver Wong
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      09-30-2005

"plork123" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Thanks for your reply
>> It's much easier to just parse the HTML data.

>
> Do you have an example/tutorial of how this is done?


I think Roedy posted an example in another branch of this thread (which
I presume you saw since you replied to it). Otherwise, general assumptions
that need to be resolved include:

Does the structure (as opposed to the content) of the HTML data change
regularly?
Can you be assured that what you get is valid HTML?
Is the author of the site actively trying to discourage "screen
scrapping"?

- Oliver


 
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Roedy Green
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Posts: n/a
 
      09-30-2005
On Fri, 30 Sep 2005 14:57:54 GMT, "Oliver Wong" <(E-Mail Removed)>
wrote or quoted :

> Can you be assured that what you get is valid HTML?

This is a biggy. A parser can get blown out the water pretty easily.
So in practice you use indexOf to look for begin/end marker strings,
and strip out what does not matter. Usually the data part you want is
pretty regular, often machine generated.

You are always at the mercy of the provider. They can make changes at
any time perhaps intentionally to foil you.
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.
 
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