带有摆动mysql和配置文件的applet在eclipse中有效，但在浏览器中失败

Question

Hi it's probably because i'm a noob, but i'm trying to get this working for days now so hope that someone can help me....

The idea: For a java training i need to make a Java applet that reads and writes data from a (localhost) MySQL database. The settings from this database have to come out of a config.ini file.

The application runs fine as an applet and a java application in Eclipse. It also runs fine as an executable jar file.

I can't get it running as an applet though...:(.

The first error that i got was about reading the config.ini file. I expect that this happens because of the security limitations (io). It is something that needs to be solved but not my main concern for now.

In order to see if the rest works i skip my loadIni class. Then i got a: driver not found exception. I solved this by loading the mySQL jar as an archive in my applet ().

But now i'm lost...

When i start the applet in the browser i get the following error in the console:

java.lang.RuntimeException: java.lang.ExceptionInInitializerError
at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.instantiateApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.initAppletAdapter(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ExceptionInInitializerError
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at Kreta.DBConnection.<init>(DBConnection.java:39)
    at Kreta.AfhaalMenus.<init>(AfhaalMenus.java:21)
    at Kreta.test2.<init>(test2.java:39)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter$1.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$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 sun.plugin2.applet.AWTAppletSecurityManager.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)
    ... 31 more

I really hope that somebody can send me in the right direction.

Answer 1

Applets are not allowed to do a number of things, including file I/O and various networking tasks; as your applet is trying to do one. You may need to sign you applet.

Check this reference

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

Answer 2

The answer is signing all jars.

how to do this was still a quest but the following post made it really easy:

how do i sign a java applet

Answer 3

1. An applet should not have direct access to the DB. This is for the security of the DB. Instead it should be forced to go through a web service that (limits what the user can do &) itself interacts with the DB.
2. An applet communicating with a DB (or a web service) on the same host that served it can be sand-boxed.
3. If that 'reading properties' error is part of the DB connection code you do not control, that is a good case for hiding the DB access behind the web service. Otherwise there are ways of reading a properties file (from the originating server) that do not invoke an AccessControlException .

Having said all that, it is getting to the stage where unsigned code is likely to be blocked before it is ever loaded, so perhaps the first thing you should do is digitally sign the applet and all required libraries.

---

Why code an applet? If it is due to spec. by teacher, please refer them to Why CS teachers should stop teaching Java applets . This will be easier to do with a standard desktop app. launched using Java Web Start . The security environment will be the same, but a free-floating app. is:

1. A better experience for the end user.
2. A lot easier to code and maintain than an applet embedded in a web page.