Published: Wednesday, March 08, 2000
Creating Zip Files on the Fly
By James Felton
In many large scale or user-based ASP projects, a large number of files need to be made
available for download. It is inconvenient for users to have to download files one at
a time as this would take a lot of their time and care to do so. A solution? Zip the
files. Normally this needs to be done manually - but what if it is not possible to do
this? What if the server is going to be inaccessable, or what if the number of files
is going to greatly increase every day, or the users can select a dynamic number of
files to download? Ladies and Gentlemen, I bring you the ZipFunctions component!
What is it?
It is an open-source component written in Java. It is completely free, and grants the
magic ability to gzip a single file, or zip one or more files. It has been tested
thoroughly under PWS and IIS 4.0.
Installing the component
First download the component and then
copy the ZipFunctions.class file into the windows\java\trustlib
directory. If you are a Java developer, then you may want to edit the source code. When
it comes to compiling, simply compile as normal (optimise with the -O flag
if you are using Sun's JDK) and then copy the file into windows\java\trustlib.
Using the component
A testing function is integrated into the component. This allows you to check to see if
the component installed correctly. To use it the code is as follows:
<%
Dim strResult
'Create an instance of the component
set javaObject = GetObject("java:ZipFunctions")
'Execute the test method and output its result
strResult = javaObject.test()
response.write strResult
'Clean up!
set javaObject = nothing
%>
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if the component was installed correctly, then you should see the text: test ok!
as an output.
GZipping a file (gzip if a format usually used on UNIX boxes)
To GZip a file, simply use the code below:
<%
Dim strResult
'Create an instance of the component
set javaObject = GetObject("java:ZipFunctions")
'GZip a file using the GZipFile method
strResult = javaObject.GZipFile(Server.mappath("/asp/zipme.txt"), _
Server.mappath("/asp/zipme.txt.gz"))
'Output strResult
response.write strResult
'Clean up!
set javaObject = nothing
%>
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This will compress the file zipme.txt into the file zipme.txt.gz.
No files get deleted in the process, although if there is already a zipme.txt.gz
it will be overwritten. Only one file can be GZipped at a time. If an error occurs, it
will be stated in strResult. If everything goes to plan, then
strResult will read Created filename. where filename
is the file which was written to.
To create a link to the file, you must hack through this output a bit. The following
code demonstrates how to take the output of a successful strResult and
output a link to the newly created GZip file:
'Display a link to the newly created GZip file
Dim strLink
strLink = Replace(Replace(strResult, "Created " & _
Server.MapPath("/"), ""), "\", "/")
strLink = Left(strLink, Len(strLink) - 1)
Response.Write "<A HREF=""" & strLink & """>"
Response.Write strLink & "</A>"
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Simply replace the response.write strResult in the GZip example with
the code seen above to output a link to the newly created GZip file.
Zipping files
Zipping multiple files requires a slightly different procedure. The files are all passed
as a string, with each filename being separated by an asterisk (*). If only
one file is passed, no asterisk is needed, so the string could be something like:
file1.gif. If two files are passed then one asterisk is needed and the
string would look something like this: file1.gif*file2.htm. Adding another
file, another asterisk is needed and the string would become file1.gif*file2.htm*file3.zip.
To create the zip file, the following code is used:
<%
Dim strResult, theFiles
theFiles = Server.mappath("/asp/somefile.txt") & "*" & _
Server.mappath("/asp/anotherfile.zip")
set javaObject = GetObject("java:ZipFunctions")
strResult = javaObject.ZipFile(theFiles, _
Server.mappath("/asp/zipfile.zip"))
response.write strResult
set javaObject = nothing
%>
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This compresses the file somefile.txt and anotherfile.zip into
the file zipfile.zip. Once again, if zipfile.zip already
exists, it will be overwritten. Any errors will be reported in strResult.
Again, if no errors occur, then strResult will read
Created filename. where filename is the zip file that was
written. Finally, if you want to display a link to the newly created zip file, simply
replace the response.write strResult line in the above code with:
'Display a link to the newly created GZip file
Dim strLink
strLink = Replace(Replace(strResult, "Created " & _
Server.MapPath("/"), ""), "\", "/")
strLink = Left(strLink, Len(strLink) - 1)
Response.Write "<A HREF=""" & strLink & """>"
Response.Write strLink & "</A>"
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Potential Uses and Updates
There are a large number of uses for this component, but beware - zipping takes up a
lot of processing, and the more large files you compress, the longer it will take.
Constant zipping could cause problems to your server if it is not very powerful.
It would be fairly simple to zip a whole directory, certain files, databases, etc. The
type of site that ZipFunctions will be used on is the only thing that can determine the
potential uses of the component.
Updates will be few and far between. The next version of ZipFunctions will come out in
about 5-6 weeks and will be available from
http://www4.ewebcity.com/javaasp.
Happy Programming!
Attachments
Download ZipFunctions.class
Visit the Java-ASP HomePage
