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Servlet: Now logs a message on context startup to aid debugging.

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+ bonus generic refactorings
This commit is contained in:
Harald Kuhr
2023-03-09 12:17:20 +01:00
parent 77c98c917e
commit 25cd351eee
2 changed files with 30 additions and 26 deletions
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36
servlet/src/main/java/com/twelvemonkeys/servlet/image/IIOProviderContextListener.java
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@@ -37,6 +37,7 @@ import java.util.List;
import javax.imageio.ImageIO;
import javax.imageio.spi.IIORegistry;
import javax.imageio.spi.ServiceRegistry;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
@@ -57,31 +58,38 @@ import javax.servlet.ServletContextListener;
public final class IIOProviderContextListener implements ServletContextListener {
public void contextInitialized(final ServletContextEvent event) {
event.getServletContext().log("Scanning for locally installed ImageIO plugin providers");
// Registers all locally available IIO plugins.
ImageIO.scanForPlugins();
}
public void contextDestroyed(final ServletContextEvent event) {
ServletContext servletContext = event.getServletContext();
// De-register any locally registered IIO plugins. Relies on each web app having its own context class loader.
final IIORegistry registry = IIORegistry.getDefaultInstance();
final LocalFilter localFilter = new LocalFilter(Thread.currentThread().getContextClassLoader()); // scanForPlugins uses context class loader
LocalFilter localFilter = new LocalFilter(Thread.currentThread().getContextClassLoader()); // scanForPlugins uses context class loader
IIORegistry registry = IIORegistry.getDefaultInstance();
Iterator<Class<?>> categories = registry.getCategories();
while (categories.hasNext()) {
Class<?> category = categories.next();
Iterator<?> providers = registry.getServiceProviders(category, localFilter, false);
deregisterLocalProvidersForCategory(registry, localFilter, categories.next(), servletContext);
}
}
// Copy the providers, as de-registering while iterating over providers will lead to ConcurrentModificationExceptions.
List<Object> providersCopy = new ArrayList<>();
while (providers.hasNext()) {
providersCopy.add(providers.next());
}
private static <T> void deregisterLocalProvidersForCategory(IIORegistry registry, LocalFilter localFilter, Class<T> category, ServletContext context) {
Iterator<T> providers = registry.getServiceProviders(category, localFilter, false);
for (Object provider : providersCopy) {
registry.deregisterServiceProvider(provider);
event.getServletContext().log(String.format("Unregistered locally installed provider class: %s", provider.getClass()));
}
// Copy the providers, as de-registering while iterating over providers will lead to ConcurrentModificationExceptions.
List<T> providersCopy = new ArrayList<>();
while (providers.hasNext()) {
providersCopy.add(providers.next());
}
for (T provider : providersCopy) {
registry.deregisterServiceProvider(provider, category);
context.log(String.format("Unregistered locally installed provider class: %s", provider.getClass()));
}
}