NoClassDefFoundError with jdbc applet

问题

I created an applet using Eclipse:

package gui;
public class MyApplet extends JApplet {

This applet needs two external jar's: proj.jar and firebirdsql-full.jar (jdbc)

Therefore I created the HTML like this, in the same folder as the jars:

<APPLET CODE="gui.MyApplet.class" width="650" height="650" ARCHIVE="proj.jar,myApplet.jar,firebirdsql-full.jar">
    <a href="http://java.com/en/download/index.jsp">Java</a>
</APPLET>

I also tried to change the jar order in the ARCHIVE attribute.

However I keep on receiving the following error (in the java console):

Exception in thread "thread applet-gui.MyApplet.class-2" java.lang.NoClassDefFoundError: Could not initialize class org.firebirdsql.jdbc.FBDriver
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at db.DAO.getDBConnection(DAO.java:45)
    at db.MyDAO.initPreparedStatements(MyDAO.java:37)
    at db.MyDAO.<init>(MyDAO.java:33)
    at db.MyDAO.getInstance(MyDAO.java:27)
    at model.Controller.<init>(Controller.java:27)
    at gui.MyApplet.getJTabbedPane(MyApplet.java:81)
    at gui.MyApplet.getJContentPane(MyApplet.java:69)
    at gui.MyApplet.init(MyApplet.java:52)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Am I missing something?

Edit:

Somehow, while debugging this, I also received a different stacktrace:

Exception in thread "thread applet-gui.MyApplet.class-1" 
java.lang.ExceptionInInitializerError
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at db.DAO.getDBConnection(DAO.java:45)
    at db.MyDAO.initPreparedStatements(MyDAO.java:37)
    at db.MyDAO.<init>(MyDAO.java:33)
    at db.MyDAO.getInstance(MyDAO.java:27)
    at model.Controller.<init>(Controller.java:27)
    at gui.MyApplet.getJTabbedPane(MyApplet.java:81)
    at gui.MyApplet.getJContentPane(MyApplet.java:69)
    at gui.MyApplet.init(MyApplet.java:52)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.security.AccessControlException: access denied (java.util.PropertyPermission FBLog4j 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 org.firebirdsql.logging.LoggerFactory.getLogger(LoggerFactory.java:36)
    at org.firebirdsql.logging.LoggerFactory.getLogger(LoggerFactory.java:72)
    at org.firebirdsql.jdbc.FBDriver.<clinit>(FBDriver.java:63)
    ... 12 more

回答1:

Now that we see the second stack trace, it's clear what's happening: the JDBC driver is trying to use Log4J for logging. It's trying to get logging parameters from a system property in the static initializer of the driver class, and it's failing because unsigned applets don't have permission to read system properties.

You can sign your applet and grant that property (java.util.PropertyPermission FBLog4j read) to it, but in all honesty, this does not bode well; I'd expect it to throw some other security exception as soon as you fixed this one. If this driver hasn't been written to work from an applet, it's likely that it'll be a fool's errand trying.

回答2:

Unsigned applets are running in a 'restricted' sandbox, so to speak. More info here over at Oracle's documentation: http://docs.oracle.com/javase/tutorial/deployment/applet/security.html

My guess, much like the exception says, is that FBDriver.java:63 (inside Firebird ) is doing something that the JVM won't allow.

By the way, it is a bit odd to load a JDBC driver inside an applet, but I digres..

来源：https://stackoverflow.com/questions/10673119/noclassdeffounderror-with-jdbc-applet

标签

java

jdbc

applet

firebird

noclassdeffounderror