CustomSerializer

XML-RPC Custom Serializer

Redstone XML-RPC has the ability to add custom serializer classes to convert our model objects to XML-RPC structs.

Here are the steps to adding a new custom serializer. We used to convert objects into HashMaps then allow Redstone to serialize the maps, but this required a two stage conversion which is costly.

• implement XmlRpcCustomSerializer
• getSupportedClass should return the class you can serialize.
• the serialize method should make use of other serializers by calling XmlRpcSerializer.serialize

Quick steps

• implement XmlRpcCustomSerializer

• return the class you support from getSupportedClass

• implement serialize method to append XML-RPC formatted text to the StringBuffer

• add an entry to SerializerRegistry.java

• DONE

Example

#!java
/**
 * ManagedServerGroupSerializer is a custom serializer for the XMLRPC library.
 * It converts an ServerGroup to an XMLRPC <struct>.
 * @version $Rev$
 * @xmlrpc.doc
 *      #struct("Server Group")
 *          #prop("int", "id")
 *          #prop("string", "name")
 *          #prop("string", "description")
 *          #prop("int", "org_id")
 *          #prop("int", "system_count")
 *      #struct_end()
 *          
 */

Every serializer needs to document what it will output in terms of XML-RPC data structures. Look around at other serializers to see the different documentation types. This javadoc is very important as this is how we auto-generate the API docs.

#!java
public class ManagedServerGroupSerializer implements XmlRpcCustomSerializer {

    public static final String MAX_MEMBERS = "max_system_count";
    public static final String CURRENT_MEMBERS = "system_count";

    /** {@inheritDoc} */
    public Class getSupportedClass() {
        return ManagedServerGroup.class;
    }

The getSupportedClass should return the top most class that this serializer can serialize. For instance, to serialize a List, LinkedList, etc. you'd return Collection.class.

#!java
    /**
     * Converts a ServerGroup to a XMLRPC <struct> containing the top-
     * level fields of the ServerGroup. It serializes the Org as just an ID
     * instead of traversing the entire object graph.
     * @param value ServerGroup object.
     * @param output Buffer to serialize the object to.
     * @param builtInSerializer basic XMLRPC serializer
     * @throws XmlRpcException thrown if a problem occurs with serializing
     * the value.
     * @throws IOException thrown if a problem occurs with serializing
     * the value.
     */
    public void serialize(Object value, Writer output, XmlRpcSerializer builtInSerializer)
        throws XmlRpcException, IOException {

        ServerGroup sg = (ServerGroup) value;

        SerializerHelper serializer = new SerializerHelper(builtInSerializer);
        serializer.add("id", sg.getId());
        serializer.add("name", sg.getName());
        serializer.add("description", sg.getDescription());
        serializer.add(CURRENT_MEMBERS, sg.getCurrentMembers());
        serializer.add("org_id", sg.getOrg().getId());
        serializer.writeTo(output);
    }

XmlRpcSerializer.serialize is used to serialize common java.lang objects. The main thing to consider is how far down the object graph to go.