Post summary: Dropwizard’s performance highly degrades when using REST with XML caused by Jersey’s Abstract JAXB provider. Solution is to inject your own JAXB provider.
Dropwizard is a Java-based framework for building a RESTful web server in very short time. I have created a short tutorial how to do so in Build a RESTful stub server with Dropwizard post.
Short overview
The current application is a Dropwizard based serving as a hub between several systems. Running on Java 7, it receives REST with XML and sends XML over REST to other services. JAXB is a framework for converting XML document to Java objects and vice versa. In order to do so, JAXB needs to instantiate a context for each and every Java object. Context creation is an expensive operation.
Problem
Jersey’s Abstract JAXB provider has weak references to JAXB contexts by using WeakHashMap. This causes context’s map to be garbage collected very often and new contexts to be added again to that map. Both garbage collection and context creation are expensive operations causing 100% CPU load and very poor performance.
Solution
The solution is to create your own JAXB context provider which keeps context forever. One approach is HashMap with context created on the fly on first access of specific Java object:
import javax.ws.rs.ext.ContextResolver;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import java.util.HashMap;
import java.util.Map;
public class CustomJAXBContextProvider implements ContextResolver<JAXBContext> {
private static final Map<Class, JAXBContext> JAXB_CONTEXT
= new HashMap<Class, JAXBContext>();
public JAXBContext getContext(Class<?> type) {
try {
JAXBContext context = JAXB_CONTEXT.get(type);
if (context == null) {
context = JAXBContext.newInstance(type);
JAXB_CONTEXT.put(type, context);
}
return context;
} catch (JAXBException e) {
// Do something
return null;
}
}
}
Another approach is one big context created for all the Java objects from specific packages separated with a colon:
import javax.ws.rs.ext.ContextResolver;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
public class CustomJAXBContextProvider implements ContextResolver<JAXBContext> {
private static JAXBContext jaxbContext;
public JAXBContext getContext(Class<?> type) {
try {
if (jaxbContext == null) {
jaxbContext = JAXBContext
.newInstance("com.acme.foo:com.acme.bar");
}
return jaxbContext;
} catch (JAXBException e) {
// Do something
return null;
}
}
}
Both approaches have pros and cons. The first approach has fast startup time, but the first request will be slow. The second approach will have a fast first request, but slow server startup time. Once JAXB context is created in Dropwizard Application class a Jersey client should be created with this context and used for REST requests:
Client client = new JerseyClientBuilder(environment)
.using(configuration.getJerseyClientConfiguration())
.withProvider(CustomJAXBContextProvider.class).build(getName());
Conclusion
There is no practical need to garbage collect JAXB context so it should stay as long as application lives. This is why custom JAXB provider is a good solution even there are not actual performance issues.
