Freemarker removeIntrospectionInfo does not work with DCEVM after model hotswap

Question

I am using Freemarker and DCEVM+HotSwapManager agent. This basically allows me to hotswap classes even when adding/removing methods.

Everything works like charm until Freemarker uses hotswapped class as model. It's throwing freemarker.ext.beans.InvalidPropertyException: No such bean property on me even though reflection shows that the method is there (checked during debug session).

I am using

final Method clearInfoMethod = beanWrapper.getClass().getDeclaredMethod("removeIntrospectionInfo", Class.class);
clearInfoMethod.setAccessible(true);
clearInfoMethod.invoke(clazz);

to clear the cache, but it does not work. I even tried to obtain classCache member field and clear it using reflection but it does not work too.

What am I doing wrong? I just need to force freemarker to throw away any introspection on model class/classes he has already obtained.

Is there any way?

UPDATE

Example code

Application.java

// Application.java
public class Application
{
    public static final String TEMPLATE_PATH = "TemplatePath";
    public static final String DEFAULT_TEMPLATE_PATH = "./";

    private static Application INSTANCE;
    private Configuration freemarkerConfiguration;
    private BeansWrapper beanWrapper;

    public static void main(String[] args)
    {
        final Application application = new Application();
        INSTANCE = application;
        try
        {
            application.run(args);
        }
        catch (InterruptedException e)
        {
            System.out.println("Exiting");
        }
        catch (IOException e)
        {
            System.out.println("IO Error");
            e.printStackTrace();
        }
    }

    public Configuration getFreemarkerConfiguration()
    {
        return freemarkerConfiguration;
    }

    public static Application getInstance()
    {
        return INSTANCE;
    }

    private void run(String[] args) throws InterruptedException, IOException
    {
        final String templatePath = System.getProperty(TEMPLATE_PATH) != null
                ? System.getProperty(TEMPLATE_PATH)
                : DEFAULT_TEMPLATE_PATH;

        final Configuration configuration = new Configuration();
        freemarkerConfiguration = configuration;

        beanWrapper = new BeansWrapper();
        beanWrapper.setUseCache(false);
        configuration.setObjectWrapper(beanWrapper);
        try
        {
            final File templateDir = new File(templatePath);
            configuration.setTemplateLoader(new FileTemplateLoader(templateDir));
        }
        catch (IOException e)
        {
            throw new RuntimeException(e);
        }

        final RunnerImpl runner = new RunnerImpl();
        try
        {
            runner.run(args);
        }
        catch (RuntimeException e)
        {
            e.printStackTrace();
        }
    }

    public BeansWrapper getBeanWrapper()
    {
        return beanWrapper;
    }
}

RunnerImpl.java

// RunnerImpl.java
public class RunnerImpl implements Runner
{
    @Override
    public void run(String[] args) throws InterruptedException
    {
        long counter = 0;
        while(true)
        {
            ++counter;
            System.out.printf("Run %d\n", counter);
//          Application.getInstance().getFreemarkerConfiguration().setObjectWrapper(new BeansWrapper());
            Application.getInstance().getBeanWrapper().clearClassIntrospecitonCache();
            final Worker worker = new Worker();
            worker.doWork();
            Thread.sleep(1000);
        }
    }

Worker.java

// Worker.java
public class Worker
{
    void doWork()
    {
        final Application application = Application.getInstance();
        final Configuration freemarkerConfiguration = application.getFreemarkerConfiguration();

        try
        {
            final Template template = freemarkerConfiguration.getTemplate("test.ftl");
            final Model model = new Model();
            final PrintWriter printWriter = new PrintWriter(System.out);

            printObjectInto(model);
            System.out.println("-----TEMPLATE MACRO PROCESSING-----");
            template.process(model, printWriter);
            System.out.println();
            System.out.println("-----END OF PROCESSING------");
            System.out.println();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        catch (TemplateException e)
        {
            e.printStackTrace();
        }
    }

    private void printObjectInto(Object o)
    {
        final Class<?> aClass = o.getClass();
        final Method[] methods = aClass.getDeclaredMethods();
        for (final Method method : methods)
        {
            System.out.println(String.format("Method name: %s, public: %s", method.getName(), Modifier.isPublic(method.getModifiers())));
        }
    }
}

Model.java

// Model.java    
public class Model
{
    public String getMessage()
    {
        return "Hello";
    }

    public String getAnotherMessage()
    {
        return "Hello World!";
    }
}

This example does not work at all. Even changing BeansWrapper during runtime won't have any effect.

Answer 1

BeansWrapper (and DefaultObjectWrapper's, etc.) introspection cache relies on java.beans.Introspector.getBeanInfo(aClass), not on reflection. (That's because it treats objects as JavaBeans.) java.beans.Introspector has its own internal cache, so it can return stale information, and in that case BeansWrapper will just recreate its own class introspection data based on that stale information. As of java.beans.Introspector's caching, it's in fact correct, as it builds on the assumption that classes in Java are immutable. If something breaks that basic rule, it should ensure that java.beans.Introspector's cache is cleared (and many other caches...), or else it's not just FreeMarker that will break. At JRebel for example they made a lot of effort to clear all kind of caches. I guess DCEVM doesn't have the resources for that. So then, it seems you have to call Introspector.flushCaches() yourself.

Update: For a while (Java 7, maybe 6) java.beans.Introspector has one cache per thread group, so you have call flushCaches() from all thread groups. And this all is actually implementation detail that, in principle, can change any time. And sadly, the JavaDoc of Introspector.flushCaches() doesn't warn you...