JAXB creating context and marshallers cost

Question

The question is a bit theoretical, what is the cost of creating JAXB context, marshaller and unmarshaller?

I\'ve found that my code could benefit from keeping the sa

Answer 1

I usually solve problems like this with a ThreadLocal class pattern. Given the fact that you need a different marshaller for each Class, you can combine it with a singleton-map pattern.

To save you 15 minutes, of work. Here follows my implementation of a thread-safe Factory for Jaxb Marshallers and Unmarshallers.

It allows you to access the instances as follows ...

Marshaller m = Jaxb.get(SomeClass.class).getMarshaller();
Unmarshaller um = Jaxb.get(SomeClass.class).getUnmarshaller();

And the code you will need is a little Jaxb class that looks as follows:

public class Jaxb
{
  // singleton pattern: one instance per class.
  private static Map singletonMap = new HashMap<>();
  private Class clazz;

  // thread-local pattern: one marshaller/unmarshaller instance per thread
  private ThreadLocal marshallerThreadLocal = new ThreadLocal<>();
  private ThreadLocal unmarshallerThreadLocal = new ThreadLocal<>();

  // The static singleton getter needs to be thread-safe too, 
  // so this method is marked as synchronized.
  public static synchronized Jaxb get(Class clazz)
  {
    Jaxb jaxb =  singletonMap.get(clazz);
    if (jaxb == null)
    {
      jaxb = new Jaxb(clazz);
      singletonMap.put(clazz, jaxb);
    }
    return jaxb;
  }

  // the constructor needs to be private, 
  // because all instances need to be created with the get method.
  private Jaxb(Class clazz)
  {
     this.clazz = clazz;
  }

  /**
   * Gets/Creates a marshaller (thread-safe)
   * @throws JAXBException
   */
  public Marshaller getMarshaller() throws JAXBException
  {
    Marshaller m = marshallerThreadLocal.get();
    if (m == null)
    {
      JAXBContext jc = JAXBContext.newInstance(clazz);
      m = jc.createMarshaller();
      marshallerThreadLocal.set(m);
    }
    return m;
  }

  /**
   * Gets/Creates an unmarshaller (thread-safe)
   * @throws JAXBException
   */
  public Unmarshaller getUnmarshaller() throws JAXBException
  {
    Unmarshaller um = unmarshallerThreadLocal.get();
    if (um == null)
    {
      JAXBContext jc = JAXBContext.newInstance(clazz);
      um = jc.createUnmarshaller();
      unmarshallerThreadLocal.set(um);
    }
    return um;
  }
}