JAXB Tip: one line of code to marshall and unmarshall xml.

4 Comments Published May 26th, 2011 in Java Tags: Java, JAXB, quick tip, shortening code, tip, XML.

I wrote in a previous article how easy it is to translate Java object to/from XML, without adding exotic library dependencies to your project; recently I’ve going through the code of one of my colleague and I discovered that the 3 line necessary to marshal and un-marshal the XML can be shortened to a single line using the JAXB utility class:

JAXBContext context = JAXBContext.newInstance(ObjectToConvert.class);
Unmarshaller u = context.createUnmarshaller();
return (ObjectToConvert) u.unmarshal(xmlInputStream);

// becomes
return (ClassToConvert)JAXB.unmarshal(xmlInputStream, ObjectToConvert.class);

// and 
JAXBContext context = JAXBContext.newInstance(objectInstanceToConvert.getClass());
Marshaller m = jc.createMarshaller();
m.marshal(objectInstanceToConvert, xmlOutputStream);

// becomes
JAXB.marshall(objectInstanceToConvert, xmlOutputStream)

Nice: one line of code to convert Java objects from/to XML. I didn’t notice this utility method in the JAXB library at first, so I was implementing those two methods in my code, more or less the same way. It’s always good to remove code.

4 Responses to “JAXB Tip: one line of code to marshall and unmarshall xml.”

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1 Blaise Doughan May 26th, 2011 at 16:57

Hi Luigi,

One thing to be aware of is that while using the JAXB class requires less lines of code, it does not provide the best performance. Normally the metadata processing is done at context creation time, then since the JAXBContext is thread safe it can be reused. When you use the JAXB class, the metadata initialization hit is taken for each marshal and unmarshal opertation.

-Blaise
2 Tim Dec 6th, 2011 at 01:25

In addition, in at least some implementations of JAXB, each call to create a JAXBContext object will result in the creation of an anonymous class that does not get garbage collected. So over time, you’ll run out of memory (PermGen, presumably, though I haven’t tried to reproduce the problem directly in order to confirm that). If you’re just running the occasional unmarshal operation, you won’t care about either of these things, but if you’re doing lots of unmarshal operations, then reusing a single JAXBContext will make a big difference in both respects.

References:
http://whileonefork.blogspot.com/2010/09/leaking-of-jaxb.html
http://stackoverflow.com/questions/3584821/jaxbcontext-newinstance-memory-leak
3 Luigi Dec 6th, 2011 at 23:09

Awesome comment Tim, thanks for sharing.