How to connect to SQL database from applet

Question

I am making an applet that connects to a database that is stored on the same web server, and when I test the code in the applet viewer in Eclipse, it connects. Problem is, when I try to run it outside Eclipse (on web server or locally), I get this error:

Exception in thread "AWT-EventQueue-2" java.lang.ExceptionInInitializerError
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:286)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.j_ctrl.MovePanel.connectDB(MovePanel.java:569)
at com.j_ctrl.MovePanel.showHighScore(MovePanel.java:558)
at com.j_ctrl.MovePanel.enterPress(MovePanel.java:544)
at com.j_ctrl.MovePanel$1.keyPressed(MovePanel.java:163)
at java.awt.Component.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Caused by: java.security.AccessControlException: access denied       (java.util.PropertyPermission file.encoding read)
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPropertyAccess(Unknown Source)
at java.lang.System.getProperty(Unknown Source)
at com.mysql.jdbc.StringUtils.<clinit>(StringUtils.java:70)
... 39 more

Is there anything special that needs to be done in order to connect to an SQL database from an applet? Here is the code that handles the connection:

private void connectDB(){
    try{
        String driverName = "com.mysql.jdbc.Driver";
        Class.forName(driverName);
        String url = "jdbc:mysql://localhost/database";
        String user = "user";
        String pass = "pass";
        connection = DriverManager.getConnection(url, user, pass);
        System.out.println("Connected");
    }catch(Exception ex){
        ex.printStackTrace();
    }
}

I changed the username, password and database here, but in my code they are correct.

Edit

Since connecting to the SQL server didn't work (I imagine it was hosted on a different host), I have ended up changing the way I access the database. The applet opens a connection to a PHP file on the host, which in turn connects to the database. Either way this is more secure.

Shaun · Accepted Answer · 2011-12-01 04:07:48Z

1

This is being caused by the security model for applets. Here's a good article summarizing the two main ways around this issue - either sign the applet or use a policy file. Let us know if you still experience problems after trying one of these:

http://www.coderanch.com/how-to/java/HowCanAnAppletReadFilesOnTheLocalFileSystem

answered Dec 1, 2011 at 4:07

Shaun

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2 Comments

Andrew Thompson Over a year ago

I don't especially like the mention of policy files to newbies since it is an entirely impractical way to distribute a real world applet, but since the Java Ranch description has a passage explaining the down-side, I decided to let it slide this time.

JCtrl Over a year ago

Says on CodeRanch that and unsigned applet "can only make network connections back to the host from which they were served", but I can't connect to the host using my unsigned applet.

Tom · Accepted Answer · 2012-03-29 03:00:03Z

1

You need to sign your applet. Here is some good documentation on how.

edited Mar 29, 2012 at 3:00

answered Dec 1, 2011 at 5:10

Tom

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1 Comment

Andrew Thompson Over a year ago

Good answer, though you might want to swap out the Sun link for this one at Oracle.

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