Creating an application with Google Web Toolkit that interacts with MySQL

Question

I've created a web application in Java with Google Web Toolkit (GWT). On the client side, GWT generates an input box and (using the GWT search api) conducts a web search. I'd like to push some of the information from the web search into a MySQL database so that it can be analysed using a machine learning application (Weka). I've got an RPC running that interacts with server side code. In that server side code, I tried to establish a connection to the MySQL database.

I'm currently running the project locally, so, as far as I can tell, google app engine is hosting it. This is supported by the fact that when I run the application I get the following message:

Initializing AppEngine server
Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger  
The server is running at http://localhost:8888/

However, although I'm able to use the search part of the application, it throws an exception when trying to connect with my MySql database.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.  
Caused by: java.security.AccessControlException: access denied (java.net.SocketPermission mysql.database.location resolve)

I've tested the database connection from a regular (non-web based) Java program and there's no problem connecting to it from outside of the web application. I believe that I'm getting this error because google app engine won't allow connections to outside databases.

In short my questions are:
1. Although I'm using Google App Engine, is it possible to use a server side code to connect to MySQL? (I'm assuming no, but this would be ideal).
2. Is it possible to switch to another server (like Tomcat)? If so, can anyone point me to references about how to do this? I found an old stackoverflow question about how to use tomcat (http://stackoverflow.com/questions/2208181/gwt-app-deploying-on-tomcat-or-any-other-servlet-container) but it no longer directs to a place that has information about using other servers.

Thanks for your help and please feel free to ask follow up questions if you'd like me to provide more info.

Igor Artamonov Igor Artamonov · Accepted Answer · 2011-02-28T07:04:51

GAE disallow any access to other servers. You can use URLFetch service, but it's probably not what you want, and you cant use it for MySQL connection. BTW, you can create your own, http based protocol, for interacting with your other modules, but it's may be too complicated.
GWT compiles to javascript, and it works only on client-side, so it' doesn't matter what you're using on your server side, it could be used any programming language and any webserver (remember that you can use JSON to communicate, instead of default protocol). It's just default implementation of RPC build using java servlets, and you can use it inside any java web container, including tomcat. GWT was developed few years before GAE, it's totally independent projects, and it isn't requires to use GAE for server side.

Creating an application with Google Web Toolkit that interacts with MySQL

1 Answers