Question

I’m developing a web application in which users are allowed to upload pictures, the system will then generate thumbs for them.

My problem relies on the fact that EJBs can be distributed on several servers and thus are not allowed to handle files directly. I could store the images in the databases but I was hoping to store them as files in one of the servers. How can I do this? Is there any way to centralize the storage of files? Or any approach to deal with files in Java EE with EJBs?

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Currently, I’m storing my files in a database. So I have centralized access and I don’t need a dedicated file server. I’m doing this because I don’t know how to integrate ftp servers and EJBs. Is this however a good alternative?

What I want is: Using Stateless EJBs, store the uploaded images as files and the path to them in the database. So I can display them using

<h:graphicImage ... />

Answer 1

You actually have four aspects here,

1. Receiving and sending files
2. Creating thumbnails
3. Storing the files somewhere every node can access
4. Storing the original + thumbnail entities in a common database

Since you already have Java EE server, you probably also already have a (HTTP) servlet server, in which there is numerious ways of doing load balancing and caching, not to mention the obious potential for web-based interaction. If anything, support FTP transfer with a directory watcher as a bonus.

You should not create the thumbnails using stateless session beans, this means your servers will be crap at peak time – the server will give priority to buisness logic over making new connections. Rather, first receieve and store the file + original entity in the database, and then use a service bean to queue up thumbnail creation (maybe with n worker threads or message queues if you want). You can also use native tools in some cases, we do in linux.

You should use a shared file system, SAN, which is the right tool for sharing files across several machines. And structure your files according to your file system’s limits – like number of files per directory and read/write capacity.

And a single database will be good enough for at least a small cluster, as long as you are not killing it with big binary blobs.

If in doubt, buy more ram 😉 Especially the thumbnails are very cachable and will give good performance also in Tomcat – if you are not familiar with multi-threading, find a cache at google. Also cache the entities naturally, not only the files.