[BEANUTILS-450] BeanUtilsBean.getInstance() pseudo-singleton causes problems with Java 7 parallelized class loader

• Type: Bug
• Status: Open
• Priority: Blocker
• Resolution: Unresolved
• Affects Version/s: 1.7.0
• Fix Version/s: 2.0.0
• Component/s: Bean / Property Utils, ConvertUtils & Converters

Environment

Java 7u25+, Windows 7 32-bit desktop environments

• Assignee: Unassigned
• Reporter: Matthew Hall
• Created: 30/Oct/13 19:50
• Updated: 05/Dec/13 21:05

Description

From an email I sent to the BeanUtils users mailing 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 {
       registerConverters();
   }

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

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

   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?