Chapter 6. Marshalling

Marshalling is the process of converting Java objects into a format that is transferable over the wire. Unmarshalling is the reversal of this process where data read from a wire format is converted into Java objects.

Red Hat JBoss Data Grid uses marshalling and unmarshalling to:

Red Hat JBoss Data Grid uses the JBoss Marshalling Framework to marshall and unmarshall Java POJOs. Using the JBoss Marshalling Framework offers a significant performance benefit, and is therefore used instead of Java Serialization. Additionally, the JBoss Marshalling Framework can efficiently marshall Java POJOs, including Java classes.

The Java Marshalling Framework uses high performance java.io.ObjectOutput and java.io.ObjectInput implementations compared to the standard java.io.ObjectOutputStream and java.io.ObjectInputStream.

Instead of using the default Marshaller, which may be slow with payloads that are unnecessarily large, objects may implement java.io.Externalizable so that a custom method of marshalling/unmarshalling classes is performed. With this approach the target class may be created in a variety of ways (direct instantiation, factory methods, reflection, etc.) and the developer has complete control over using the provided stream.

import org.infinispan.marshall.AdvancedExternalizer;

public class Book {

   final String name;
   final String author;

   public Book(String name, String author) {
      this.name = name;
      this.author = author;
   }

   public static class BookExternalizer implements AdvancedExternalizer<Book> {
      @Override
      public void writeObject(ObjectOutput output, Book book)
            throws IOException {
         output.writeObject(book.name);
         output.writeObject(book.author);
      }

      @Override
      public Person readObject(ObjectInput input)
            throws IOException, ClassNotFoundException {
         return new Person((String) input.readObject(), (String) input.readObject());
      }

      @Override
      public Set<Class<? extends Book>> getTypeClasses() {
         return Util.<Class<? extends Book>>asSet(Book.class);
      }

      @Override
      public Integer getId() {
         return 2345;
      }
   }
}

Once the writeObject() and readObject() methods have been implemented the Externalizer may be linked up with the classes they externalize; this is accomplished with the getTypeClasses() method seen in the above example.

In addition, a positive identifier must be defined as seen in the getId() method above. This value is used to identify the Externalizer at runtime. A list of values used by JBoss Data Grid, which should be avoided in custom Externalizer implementations, may be found at JBoss Data Grid Externalizer IDs.

<cache-container>
  <serialization>
    <advanced-externalizer class="Book$BookExternalizer"/>
  </serialization>
</cache-container>

GlobalConfigurationBuilder builder = ...
builder.serialization()
   .addAdvancedExternalizer(new Book.BookExternalizer());

The following values are used as Externalizer IDs inside the Infinispan based modules or frameworks, and should be avoided while implementing custom marshallers.