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Notify Java or Python when a file has been uploaded with the SFTP protocol

I use several applications which upload files using the SFTP protocol to a specific directory on my server. I'ld like to write an application which will be deployed on my server, using the Java or Python programming language. This application has to be notified when a new file has been added to the directory. I'ld like to do this without polling the directory. Is this possible?

Yes - for Java 7 use a WatchService. For Python see pyinotify.
The underlying mechanism is inotify, and you can produce shell-level solutions which use inotify-tools to run a small helper application every time a file is added.

How do you access SQL database from GWT?

I've read some articles on the Internet that this is not possible. To communicate own SQL database that is located on other server from GWT application. Jetty doesn't allow it.
I found a way how to perform it but it's not very cosy. I have client and server part inside GWT. The server has to communicate with MySQL database on localhost. So I've written an ant script to build a war that I can launch on Apache Tomcat server. It works perfectly there but I'm not able to debug the code effectively.
Do you have some advices how to perform this task? I was thinking of writing the clienty only in GWT and find some waz how to communicate my own server written outside the GWT. I've found Apache Thrift for GWT but this edited library of thrift seem not to work properly.
Thank you very much for your answers:)

It is possible to communicate with a database from a GWT application. The client side has to call the methods of the server via GWT-RPC, which can communicate with any database.
Maybe Jetty does not support it (have not tested it personally) but you can develop your web application using Apache too. There you can access the database the same way as from any web application:
You will need the mysql-connector-java-5.1.20-bin.jar file (downloadable from: http://dev.mysql.com/downloads/connector/j/ ), and restart the server added to the $CATALINA_HOME/common/lib directory.
OR added to the WEB-INF/lib folder of your web application.
You can find tutorials online of how to develop an application using Tomcat instead of Jetty. For example: https://wiki.auckland.ac.nz/display/BeSTGRID/Deploying+GWT+to+Tomcat+in+Eclipse

Reshi, stop and think about how applications really work. Nobody provides web pages with javascript to read/write databases, that would be crazy and unsecure. Servers are always in themiddle of all communication in this case. You need to create services that run inside your server, one of these services will be a database layer.
Javascript cant create network connections and read/write binary data, thus it would be insane to attempt to get the gwt compiler to compile any jdbc drvier and more.

Jetty does NOT stop us from connecting to a database. All you have to do is to follow the MVP model way. Although MVP is better bet against all hurdles, at a minimal point, you would have to try not having SQL code on the client package.

Running camel in standalone mode

I have a system that consists of several thick client apps that communicate with each other. The apps currently communicate directly with each other over rmi but I a exploring options for using a messaging framework, specifically camel.
I know camel can be run in standalone (often when we do testing) but is often deployed in a container or esb. Is it appropriate to run camel in standalone mode if the only apps communicating with it are desktop (swing) apps?

Well yes and no. Camel is a message router, it helps you defining routes for your calls. However it will not help you choosing communication protocol. It just makes the integration quicker and faster (for example use JMS to communicate App1 <-> App2, RMI for App2 <-> App3 and some other protocol for App2 <-> App3).
Yes, Camel might be deployed in Standalone version. Here is link how to do this. I would advice to create separate application (I would also use Shade Maven plugin here to embed all dependencies).
You might also consider using some ESB, for example Servicemix or Fuse. However this is pretty big environment...

Actually, a vanilla installation (unzip that is) of ActiveMQ (5.5.1 for instance) will come bundled with Camel. Simply edit conf/activemq.xml and insert somewhere. Configure camel at conf/camel.xml. ActiveMQ does not come with all Camel components, so simply drop any additional camel jar file into /lib. You can easy just drop any of your own .jar files that for instance definies a RouteBuilder etc. in /lib to.

To communicate between applications I would use a standalone ActiveMQ broker (typically two instances for failover) and embed camel into the thick client applications. You can then use the pojo messaging features in camel to achieve almost transparent communication.
See my blog for an example http://www.liquid-reality.de/x/NoBe

Web server java library?

I m looking for a simple java library which would let me make a java web server and share some files. Is there any libraries which would let me achieve this?

Use jetty - the lightweight web server and servlet container.

There is a host of different web servers which all can do what you want (provided it just is allowing users to download files).
A good, small library with a simple-to-get-started method, is the Acme Laboratory Java pages.
http://acme.com/java/software/Acme.Serve.Serve.html
serves the current directory without any fuzz.

You can directly use an Apache WebServer setup for this.

Which application server should i choose for my project?

I am currently developing an application for some researchers in my university.It's a small java program that you can use by command line. The next step is to package that program and deploy it to an application server. Some clients program will submit requests to the server who will call the tool that I wrote. Lately, we will add more tools to the server and he has to dispatch the requests to the right tool.
Which application server fits my needs ? I have looked for Tomcat, Jetty and Glassfish but it seems that they are only used for web application.
Is it possible to use those servers in some context different from web context? Which package archive should i use (jar, war) ?
Any advice?

Some clients program will submit requests to the server who will call the tool that I wrote.
The big question is what server-side technology and what communication protocol can you use between the clients and the server. You basically have two major options: HTTP and web services (in that case, consider using either JAX-WS or JAX-RS) or RMI-IIOP and EJBs (in that case, you'll have to use a Java EE compliant server like GlassFish).
I have looked for Tomcat, Jetty and Glassfish but it seems that they are only used for web application.
Not really. As I said, they can also be used for web services oriented applications. And GlassFish can be used for EJBs applications.
Which package archive should i use (jar, war)
The packaging will depend on the type of application you'll write, it's not something that you choose upfront, it's just a consequence. EJBs are packaged in an EJB JAR and typically deployed inside an EAR; Servlet based web services are deployed inside a WAR.
You really need to think about what technology to use first (with the current level of detail, I can't provide more guidance).

Do you even need an application server? There's nothing stopping you from adding the necessary network bindings and deploying it on its own.
Of the servers you mention, you've got 2 different categories: servlet containers and full-stack Java EE servers
Tomcat and Jetty are servlet containers. That doesn't mean that you can only do web stuff with them and you could manually add the required libraries to get a full Java EE server.
Glassfish is a full-stack Java EE server and can be compared with JBoss (both are open source) or the commercial rivals Weblogic and Websphere.
Sometimes this question is simple as the environment you are working in mandates a particular flavour of app server. You should check this first.
If you're not forced to use an app server, I'd ask why you think you need to use an app server?

I don't see why you would want to use tomcat, glassfish or jetty for a command line program.
If it's command-line based, and you want it to run server-side, you could write a little program that allows users to, for instance, telnet to your server, which in turn starts the CLI-application in question, and relays input / output to the client.
You may also want to look into Java Webstart, which makes deployment of new versions a breeze.

Actually we can't answer with so few elements.
- What are you planning to do
- With what technologies
- Where are you planning to host your application (have you got budget?)
- In which language are written the clients (even the future ones)?
- Could clients be on mobile phones (add some technlogy constraints...)
....
It would also be great to know what kind of request the clients will do, and what kind of response the server will provide...
Actually with what you tell us, all those application servers can do what you want...
I have looked for Tomcat, Jetty and
Glassfish but it seems that they are
only used for web application
You could even make a webapplication (servlet) and on the clientside use a httpclient to call that servlet... there are so many options :)
vive Paris!