how to override a service provider in java

Question

This is more a general question by example: I\'m using xstream and woodstox, woodstox comes with a service provider for javax.xml.stream.XMLOutputFactory in woodstox jar reg

Answer 1

First: instead of relying on JDK SPI interface, I strongly recommend simplifying your life and NOT using it. It really adds no value over injecting XMLInputFactory and/or XMLOutputFactory yourself. For injection you can use Guice (or Spring); or just pass it manually. Since these factories do not have dependencies of their own, this is easy.

But if choose to (or have to) use XMLInputFactory.newInstance(), you can define a System property for "javax.xml.stream.XMLOutputFactory" and "javax.xml.stream.XMLInputFactory".

So why not use JDK approach? Multiple reasons:

1. It adds overhead: if you are not specifying System property, it will have to scan the whole classpath, and with big app servers this takes 10x-100x as long as most parsing
2. Precedence of implementations is undefined: if you multiple in classpath, which one will you get? Who knows... (and note: it might even change when you add new jars in classpath)
3. You are very likely to get multiple impl via transitive dependencies

Unfortunately, Oracle still seems to insist on adding this known-faulty method for registering service providers. Why? Probably because they do not have a DI lib/framework of their own (Guice is by google, Spring by Springsource), and they tend to be pretty control hungry.

Answer 2

I discovered that if I put the service file under WEB-INF/classes/services/javax.xml.stream.XMLOutputFactory then it will be first in classpath and before jars in WEB-INF/lib. and that's my solution.

Answer 3

We had similar issue where parsing would run in local but fail on server. After debugging found server is using reader com.ctc.wstx.evt.WstxEventReader

Whereas on local reader was com.sun.xml.internal.stream.XMLEventReaderImpl

We set following property to resolve it.

System.setProperty("javax.xml.stream.XMLInputFactory", "com.sun.xml.internal.stream.XMLInputFactoryImpl");

Answer 4

You can just do like this to specify the XMLOutputFactory implementation You want to use:

System.setProperty("javax.xml.stream.XMLOutputFactory", ... full classname You want to use ...);

Source: http://docs.oracle.com/cd/E17802_01/webservices/webservices/docs/1.6/tutorial/doc/SJSXP4.html

Deriving from JAXP, the XMLInputFactory.newInstance() method determines the specific XMLInputFactory implementation class to load by using the following lookup procedure:

1. Use the javax.xml.stream.XMLInputFactory system property.
2. Use the lib/xml.stream.properties file in the JRE directory.
3. Use the Services API, if available, to determine the classname by looking in the META-INF/services/javax.xml.stream.XMLInputFactory files in jars available to the JRE.
4. Use the platform default XMLInputFactory instance.

Answer 5

If your implementation is in a jar then make sure it is before woodstox.jar on the class path, then FactoryFinder will use your implementation.