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C.9. The Externalizer

C.9.1. About Externalizer
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An Externalizer is a class that can:
  • Marshall a given object type to a byte array.
  • Unmarshall the contents of a byte array into an instance of the object type.
Externalizers are used by Red Hat JBoss Data Grid and allow users to specify how their object types are serialized. The marshalling infrastructure used in JBoss Data Grid builds upon JBoss Marshalling and provides efficient payload delivery and allows the stream to be cached. The stream caching allows data to be accessed multiple times, whereas normally a stream can only be read once.
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C.9.2. Internal Externalizer Implementation Access
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Externalizable objects should not access Red Hat JBoss Data Grids Externalizer implementations. The following is an example of incorrect usage: 
public static class ABCMarshallingExternalizer implements AdvancedExternalizer<ABCMarshalling> {
   @Override
   public void writeObject(ObjectOutput output, ABCMarshalling object) throws IOException {
      MapExternalizer ma = new MapExternalizer();
      ma.writeObject(output, object.getMap());
   }
 
   @Override
   public ABCMarshalling readObject(ObjectInput input) throws IOException, ClassNotFoundException {
      ABCMarshalling hi = new ABCMarshalling();
      MapExternalizer ma = new MapExternalizer();
      hi.setMap((ConcurrentHashMap<Long, Long>) ma.readObject(input));
      return hi;
   }

   ...
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End user externalizers do not need to interact with internal externalizer classes. The following is an example of correct usage: 
public static class ABCMarshallingExternalizer implements AdvancedExternalizer<ABCMarshalling> {
   @Override
   public void writeObject(ObjectOutput output, ABCMarshalling object) throws IOException {
      output.writeObject(object.getMap());
   }
 
   @Override
   public ABCMarshalling readObject(ObjectInput input) throws IOException, ClassNotFoundException {
      ABCMarshalling hi = new ABCMarshalling();
      hi.setMap((ConcurrentHashMap<Long, Long>) input.readObject());
      return hi;
   }

   ... 
}
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