DWR

There is a quirk in the ability to plug classes into DWR. You need to keep the setting as a list, ie keep at least two classnames (having only one classname will make the setting be handled as a non-list setting which will go wrong later).

http://directwebremoting.org/dwr/documentation/server/configuration/servlet/plugin.html

On this page the example listed will not work as is:
<init-param>
    <param-name>org.directwebremoting.extend.ServerLoadMonitor</param-name>
    <param-value>com.example.MyCustomServerLoadMonitor</param-value>
 </init-param>

In order for this to work you need to repeat the class in a list format:
<init-param>
    <param-name>org.directwebremoting.extend.ServerLoadMonitor</param-name>
    <param-value>com.example.MyCustomServerLoadMonitor, com.example.MyCustomServerLoadMonitor</param-value>
</init-param>

Obviously, this is incorrect.

I have looked into this and here are some notes:
Relevant code from DefaultContainer
public void addParameter(String askFor, Object valueParam) throws ContainerConfigurationException
{
         Object value = valueParam;
         // Maybe the value is a classname that needs instantiating
         if (value instanceof String)
         {
             try
             {
                 Class<?> impl = LocalUtil.classForName((String) value);
                 value = impl.newInstance();
             }


When the parameter is added if it a class is found with a matching name it is instantiated.

Then in StartupUtil we get the parameter:

String abstractionImplNames = container.getParameter(LocalUtil.originalDwrClassName(ContainerAbstraction.class.getName()));

  public String getParameter(String name)
     {
         Object value = beans.get(name);
         return (value == null) ? null : value.toString();
     }

The parameter is a class and we are calling toString which gives us package.className@whatever - of course this blows up. Adding the, prevents DWR from setting the parameter value to a class which is why the list format works.