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Many web service programmers want to use types that are not directly
visible by reflection of the service interface. Here are some popular
examples of types that programmers want to use for property or
parameter types:

• Declare a base type, but transfer any one of a number of classes that extend it.
• Declare a raw Collection class, such as a Set, List, or Map, and send arbitrary objects as keys and values.
• Declare a base exception type for 'throws', and then throw other exception classes that derive from it.
• Declare an interface or an abstract type.

Aegis can handle all of these. For all except interfaces, there are
two mechanisms that involved: the root class list and xsi:type attributes.

As explained above, Aegis can write 'anything', but it can only read
objects of types that are mapped. You must give Aegis a list of all
the types that you want to use over and above those visible from the
service, and you must instruct Aegis to send xsi:type
attributes. These type attributes allow Aegis to identify the type of
these additional objects and look them up in the mappings.

Interfaces require one further step. Obviously, Aegis cannot
instantiate (run 'new') on an interface. So knowing that a particular
XML Schema type maps to an interface is not enough information. To be
able to read an XML element that corresponds to an interface, Aegis
must know a 'proxy class' that implements the interface. You must give
Aegis a mapping from interface types to proxy class names.

How does this work? The core of Aegis is the AegisContext class. Each
AegisDatabinding object has an AegisContext. (It is probably not
possible to share an AegisContext amongst databindings.)

By default, AegisDatabinding will create its own AegisContext with
default properties. To configure additional types, as well control
other options that we will examine later on, you must create the
AegisContext for yourself and specify some of its properties. Then you
pass your AegisContext object into your AegisDatabinding object.

To use additional classes or interfaces, you need to set two (or
three) properties of your AegisContext.

• rootClasses is a collection of Java Class<?> objects. These are
  added to the list of types known to Aegis. Aegis will create a
  mapping for each. For convenience, there is a rootClassNames property for use from Spring.

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• beanImplementationMap is a mapping from Class<?> to class names.
  Use this to specify proxy classes for interfaces (or abstract classes).