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POGoogle Appengine JAVA - Zip lots of images saving in Blobstore
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copied!<p>I developed a simple media library where you can choose a set of images and download them. When a client request a download, a servlet receives the blob keys to use for create a zip file and then a Task is launched for the procedure</p> <p>The task iterate through the received blob keys and zip the images into the archive. When the task has finished a mail with the download link is sent to the user.</p> <p>Here is my problem:</p> <pre><code>FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock); OutputStream blobOutputStream = Channels.newOutputStream(writeChannel); ZipOutputStream zip = new ZipOutputStream(blobOutputStream); </code></pre> <p>A single channel can handle only this amount of bytes</p> <blockquote> <p>BlobstoreService.MAX_BLOB_FETCH_SIZE</p> </blockquote> <p>Because of that, i must open and close the channel every 1mb of data i have to write (same issue for the read, but for the read i used <a href="https://stackoverflow.com/a/11105235">this code</a> and it works). or the write() method throws a null exception</p> <p>Opening and closing the channel with a normal outputStream, does not presents issue, like <a href="http://jsfiddle.net/fDrYt/" rel="nofollow noreferrer">this code</a></p> <p>But handling a Zip file i also have to manage</p> <pre><code>ZipOutputStream zip = new ZipOutputStream(blobOutputStream); ZipEntry zipEntry = new ZipEntry(image_file_name); zipOut.putNextEntry(zipEntry); // while the image has bytes to write zipOut.write(bytesToWrite); </code></pre> <p>After i wrote 1MB of data in the ZipEntry i have to close the channel and open it again.</p> <p>So here the problem: where i open a new channel i can't access to the previouse zipEntry i was writing and then i cannot continue to write the next 1MB of the image i'm processing. </p> <p>And, after a open a new channel, if i try to write on the zipEntry object (w/o re-initializing it) i get a ClosedChannel exception</p> <p><a href="http://jsfiddle.net/97r2W/" rel="nofollow noreferrer">Here</a> is the SAMPLE code i wrote, i know is not working, but explains what i am trying to do.</p> <p>My question then: How (if is possible, off course) can i create a zip file writing 1MB per time?</p> <p>I'm also available to other approaches, the thing i need is to zip some images into one zip and save it into the blobstore, if you have other ideas to make this, please tell me</p>

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