Question

I’m using GWT for a web-app and I need to access to a mySql-database. There will be only one client (The app is used on a iPad localy). Is there any way to access the database without RPC? I’m looking for a possibility to direkty query a database.

Thanks!

Answer 1

There are 2.5 reasons you cannot use gwt to directly access MySQL.

Reason #1.
GWT is compiled into Javascript. You need to open a socket to the database server. GWT does not allow you to open a socket. In fact, no unaugmented browser (before advent of html5) is able to open a socket. But you can open a socket using Flash actionscript, or HTML 5 javascript.

Reason #2.
OK, let’s say you used HTML5 sockets. And you spent 6 months writing in Javascript a JDBC connectivity. But, your websocket would still need to address a servlet on the server which would help your websocket establish a persistent connection – and mysql is unable to perform such an establishment.

Reason #3.
SLD – SOP restriction:
(Second Level Domain Same Origin Policy)
Standard browser restricts its pages to only be able to request for, and to include, content from within the same second-level domain (SLD) as the server that provided that page to the browser. Top level domains (and top-level and a half) are such as .com, .org, .net, .me.us or .co.uk. So, domain names such as google.com, fbi.gov, mit.edu are second level domains. While, mail.google.com would be a third-level domain. Therefore, GWT would work only within the confines of an SLD. Your web server must also be accessible at the same SLD as your mysql server.

SLD-SOP and tunneling requirement is to close a security hole that could have allowed any tom-rick-or-mary to log into your system thro your browser. Tunneling is always required for a browser to connect to a server other than a http server. Tunneling is when a browser exploits the web server as a yenta (yiddish for busy-body/go-between/match-maker) to get to another server.

You have no choice but to use GWT-RPC. Perhaps you don’t wish to use RPC, then you could use RequestBuilder, or Script-Include or RequestFactory. But they are all still diverse means of tunneling. http://h2g2java.blessedgeek.com/2011/06/gwt-requestbuilder-vs-rpc-vs-script.html.

There is one reason why you can connect to your database server from your gwt client:
Your database server must run httpd connection engine. That is, your gwt app would access the db server thro http. I am not familiar with which relational database has a http access available. Most probably, you would have to query thro xml or json.

However, a company I had worked for created our own http service to allow “direct” client access. “direct” is a misnomer because we used tomcat. It is stil tunneling. Any database company that offers “direct” http access is still tunneling. Tunneling – no escape from it.

You could augment the browser with Flash and write a Flash application rather than using GWT. If direct access is so essential to you, you would have to abandon GWT and develop in Flash and run a httpd engine for your database server.