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.
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.
Related
I'm thinking about what might be the best solution to create a standalone client-server application in java with these features:
Server: it must provide APIs (probably rest?)
Client: javafx webview with angularjs to make requests to webserver.
Loader; it starts the server and the client;
The user can then manage the application directly from the webview or from the browser (to the server port)
This would also be able to create in the future a "cloud" version of the application, the client instead to query the localhost will perform to a remote server.
A solution of this type is correct?
What might be useful tools for its realization and how could it be structured?
I would like in particular a solution which does not require the use of a large Java Application Server, but something more simple that it can be included as a library.
I thought same architecture which you think because it's easy. localhost binding, angularjs, bootstrap in java Webview. one of solutions is Spring MVC Rest API with embedded tomcat. it may be not lightweight.
I am creating a web application using java. I'm wondering if there is a way to detect external memory like an SD card on a client's device. Also, is Java a good language to use for an application with this functionality? Or is there something better?
Java works on the server side (your server) and won't run on the client unless you send a Java application to the client like an Applet or a JavaFX app. If using the web application only, you're unable to accomplish this with Java, if you're using the Applet/JavaFX approach, you're able to get that info but maybe you cannot send it to the server.
IMO it would be very insecure to have such features in a web application. Imagine a web application where everyone who access to it and the web application can access to your SD card, retrieve all the contents and send them through the net to the server side, thus having access to all your info and the info of every user who access to it.
Ok so I am still new to Objective C and currently learning it. I wanted to make an app where people can login and submit data to a database. I have research and found that I need to connect to a web server (I will use a Java web server) and from this server, it will communicate to the database server.
However, I am just wondering exactly how I would connect from an IPad app (that I will make in the future) to a Java App Server such as Glashfish. To do this, what kind of web app would I make (servlets?)? If I did, would I use the URL wrting method to transfer data?
I would want to use a http connection since I am using Glassfish.
Thanks
You can expose Restful API through the java web application; and access these api in your iOS app. There are many rest-client library for iOS now.
You can also write data to url connection directly, but it's tedious and complex.
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!
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.
GWT is ultimately Javascript. As noted at Are there JavaScript bindings for MySQL?
, there is currently no way of accessing MySQL from Javascript.
Therefore you can't access it from client-side GWT code.
AFAIK it's not possible, and even if it were, it would be a really bad idea. Are you sure you actually need a database? Maybe something like gwt-client-storage would be more appropriate.
EDIT
Your database would we publicly accessible and open for any sort of attacks.
EDIT 2
This may even be a better solution, as it offers support for accessing the HTML5 Database API and is targeted to iPhone/iPad.
gwt-mobile-webkit
If you were even successful in doing so, in short, doing a CTRL + U on the browser would make your database name, username, password, tables names etc visible... And done, any developer curious to know your code has a way to hack anything and everything in your server.
I think it's not possible, I mean, if you want all your data stored in DBs. I mean, GWT compiles into javascript and javascript executes on the client (typically a web browser).
If you want to access data stored somewhere (by some mean) in a server, then you have no option but RPC. If I were you, I would stop thinking in client-server paradigm (GWT was developed with that in mind). Perhaps some embedded database like H2 and then hold connections through JDBC.
I'am developing a java servlet application, and tesing it on Eclipse + Apache Tomcat (refer: http://www.vogella.de/articles/EclipseWTP/article.html#overview_wtp).
The application is now tested on the localhost and accesed by any clients on the same LAN.
Now, I need to deploy it into the web server, where everyone from anywhere can access this servlet.
Coud you guide me the way that I've to do to archive this task.
You need to have a computer accessible to everyone - i.e. placed on the internet and not behind a firewall - with the appropriate software installed (and hardened against hacker attacks).
If you do not have such a computer, you can have a look at the Google Application Engine which allows you to deploy Java web applications (with some additional restrictions) to the Google cloud. This is free for low-volume applications.
Yes, you can do it by deploying your application in the Cloud Instance. Since we cannot able to make our server instance or computer to be run always(We may come across internet connection problems, Power Fluctuation, etc.,), We have lot of problems while making our instance public(In Security perspective too). So it is better to use cloud instances.
We have many Cloud Service Providers such as AWS by Amazon, Google Cloud, Microsoft Cloud, etc.,
Take a look on this List of Cloud Services Providers.(You have links for all top 10 providers)