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From Matthew Hall <>
Subject [beanutils] BeanUtilsBean.getInstance() pseudo-singleton implications in a Java 7 parallel class loading environment
Date Thu, 24 Oct 2013 20:37:27 GMT
Hello everyone,

First off, I’m not sure that the user list is the right place for this, but I figured I’d
try before sending it right to the dev list.

We recently tracked a bug in our software that started showing up with Java 7 back to an incompatibility
between BeanUtilsBean.getInstance() pseudo-singleton instance model, Java 7’s parallelized
class loader, and the fact that we were registering Converters with ConvertUtils inside of
a static class-level block. As far as I’m able to tell, this wasn’t a problem in previous
versions of Java because the class loader was not parallelized, meaning that the class loader
that handled the registration of our converters was the same class loader that was in use
when ConvertUtilsBean.getInstance() was invoked. Now, with Java 7, it seems that there is
no guarantee that the class loader that executes the static block containing the Converter
registration is the same one in use when ConvertUtilsBean.getInstance() is invoked, meaning
that our custom Converters are not necessarily available everywhere they used to be.

I’m writing to the list today to ask three things about this situation:

  1.  First off, is this the correct explanation for the reason that it seems we’re not
guaranteed to have our custom Converters loaded in Java 7.
  2.  In order to ensure that a different class loader thread is not in use when the Converters
are registered with ConvertUtils, we’ve moved this registration from a static class-level
block into a user interface setup method that is executed before the Converters are used.
  3.  Given that Java 7 introduced parallelized class loading in the base ClassLoader and
that BeanUtilsBean builds instances on a per-classloader basis, should this issue be raised
to the BeanUtils developers?

Below you’ll find some pseudocode that illustrates our situation:

public class UtilitiesClass {
    static {
        ConvertUtils.register(new OurCustomColorConverter(), java.awt.Color.class);

public class MainGUIClass {
    public static void main(String[] args) {
        MainGUIClass mainGui = new MainGUIClass();

    public void setup() {
        UIManager.setLookAndFeel(new LookAndFeelClass());

    public void show() {
        ((OurLookAndFeelClass) UIManager.getLookAndFeel()).getColor();

public class LookAndFeelClass extends LookAndFeel {
    public java.awt.Color getColor(String colorString) {
        return (java.awt.Color) ConvertUtils.convert("someValidColorString", java.awt.Color.class);

In the above example, the cast of the results of ConvertUtils.convert to Color in LookAndFeelClass.getColor(String)
sometimes results in a runtime exception with the message “java.lang.String cannot be cast
to java.awt.Color.”. This appears to be due to the fact that ConvertUtils.convert() fails
over to the built-in String.class Converter if it cannot find a Converter for the specified
class. In production environments, it was completely unpredictable as to when this would happen
and what would make the problem go away.

The fix we implemented was to move the registration of OurCustomColorConverter() from the
static block inside of UtilitiesClass to the first line of MainGUIClass.setup(), before the
LookAndFeel is loaded. Will this fix be sufficient, or does it still suffer from the thread
issue, if that is indeed the root cause of the problem?


Matthew Hall
Enterprise Application Developer || | Intervolve, Inc.<><> | +1-919-865-4400 ext. 701

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