Andy in the Cloud

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Handling Office Files and Zip Files in Apex – Part 2

In part 1 of this blog I talked about using the Salesforce Metadata API, Static Resources the PageReference.getContent method to implement a native unzip. This blog completes the series by introducing two Visualforce Components (and subcomponents) that provide full zip and unzip capabilities. By wrapping the excellent JSZip library behind the scenes. I gave myself three main goals…

  • Easy of use for none JavaScript Developers
  • Abstraction of the storage / handling of file content on the server
  • Avoiding hitting the Viewstate Governor!

While this audience and future developers I hope will be the judge of the first, the rest was a matter of selecting JavaScript Remoting. As the primary means to exchange the files in the zip or to be zipped between the client and server.

Unzip Component

The examples provided in the Github repo utilise a Custom Object called Zip File and Attachments on that record to manage the files within. As mentioned above, this does not have to be the case, you could easily implement something that dynamically handles and/or generates everything if you wanted!

As Open Office files are zip files themselves, the following shows the result of using the Unzip Demo to unzip a xlsx file. The sheet1.xml Attachment is the actual Sheet in the file, in its uncompressed XML form. Thus unlocking access to the data within! From this point you can parse it and update it ready for zipping.

Screen Shot 2012-12-08 at 10.20.47

As a further example, the following screenshot shows the results of unzipping the GitHub repo zip download

Screen Shot 2012-12-08 at 10.10.12

The c:unzipefile component renders a HTML file upload control to capture the file. Once the user selects a file, the processing starts. It then uses the HTML5 file IO support (great blog here) to read the data and pass it to the JSZip library. This is all encapsulated in the component of course! The following shows the component in action on the Unzip Demo page.

<c:unzipfile name="somezipfile" oncomplete="unzipped(state);"
 onreceive=
 "{!$RemoteAction.UnzipDemoController.receiveZipFileEntry}" />

Screen Shot 2012-12-08 at 10.09.02

As mentioned above it uses JavaScript Remoting, however as I wanted to make the component extensible in how the file entries are handled. I have allowed the page to pass in the RemoteAction to call back on. Which should look like this..

@RemoteAction
 public static String receiveZipFileEntry(
    String filename, String path, String data, String state)

In addition to the obvious parameters, the ‘state’ parameter allows for some basic state management between calls. Since of course JavaScript Remoting is stateless. Basically what this method returns is what gets sent back in the ‘state’ parameter on subsequent calls. In the demo provided, this contains the Id of the ZipFile record used to store the incoming zip files as attachments.

The other key attribute on the component is ‘oncomplete’. This can be any fragment of JavaScript you choose (the ‘state’ variable is in scope automatically). In the demo provided it calls out to an Action Function to invoke a controller method to move things along UI flow wise, in this case redirect to the Zip File record created during the process.

Zip Component

You may have noticed on the above screenshots I have placed a ‘Zip’ custom button on the Zip File objects layout. This effectively invokes the Zip Demo page. The use cases here is to take all the attachments on the record, zip them up, and produce a Document record and finally redirect to that for download.

Screen Shot 2012-12-09 at 10.16.11

Screen Shot 2012-12-09 at 10.17.02

The c:zipfile component once again wraps the JSZip library and leverages JavaScript Remoting to request the data in turn for each zip file entry. The page communicates the zip file entries via the c:zipentry component. These can be output explicitly at page rendering time (complete with inline base64 data if you wish) or empty leaving the component to request them via JS Remoting.

<c:zipfile name="someZipfile" state="{!ZipFile__c.Id}" 
  oncomplete="receiveZip(data);"
  getzipfileentry=
     "{!$RemoteAction.ZipDemoController.getZipFileEntry}">
   <apex:repeat value="{!paths}" var="path">
     <c:zipentry path="{!path}" base64="true"/>
   </apex:repeat>
</c:zipfile>

This component generates a JavaScript method on the page based on the name of the component, e.g. someZipfileGenerate. This must be called  at somepoint by the page to start the zip process.

The action method in the controller needs to look like this.

@RemoteAction
 public static String getZipFileEntry(String path, String state)

Once again the ‘state’ parameter is used. Except in this case it is only providing what was given to the c:zipfile component initially, it cannot be changed. Instead the method returns the Base64 encoded data of the requested zip file entry.

Finally the ‘oncomplete’ attributes JavaScript is executed and the resulting data is passed back (via apex:ActionFunction) to the controller for storage (not the binding in this case is transient, always good to avoid Viewstate issues when receiving large data) and redirects the user to the resulting Document page.

Summary

Neither components are currently giving realtime updates on the zip entries they are processing, so as per the messaging in the demo pages the user has to wait patiently for the next step to occur. Status / progress messages is something that can easily be implemented within the components at a future date.

These components utilise some additional components, I have not covered. Namely the c:zip and c:unzip components. If you have been following my expliots in the Apex Metdata API you may have noticed early versions of these in use in those examples, check out the Deploy and Retrieve demos in that repo.

I hope this short series on Zip file handling has been useful to some and once again want to give a big credit to the JSZip library. If you want to study the actual demo implementations more take a look at the links below. Thanks and enjoy!

Links