mapSimpleTypeDef Attribute (The WSIT Tutorial)

The WSIT Tutorial

`mapSimpleTypeDef` Attribute

XML Schema Part 2: Datatype defines facilities for defining datatypes for use in XML Schemas. .NET platform introduced the CLR types for some of the XML schema datatypes as described in Table 11–1.

Table 11–1 CLR to XML Schema Type Mapping


CLR Type	XML Schema Type
`byte`	`xs:unsignedByte`
`uint`	`xs:unsignedInt`
`ushort`	`xs:unsignedShor`
`ulong`	`xs:unsignedLong`

However, there are no corresponding Java types that map to the XML Schema types listed in Table 11–1. Furthermore, JAXB 2.0 maps these XML schema types to Java types that are natural to Java developer. However, this results in a mapping that is not one-to-one. For example:

xs:int -> int
xs:unsignedShort -> int

The lack of a one-to-one mapping means that when XML Schema types shown in Table 11–1 are used in an xsi:type construct, they won’t be preserved by default across an unmarshal followed by marshal operation. For example:

// C# web method
public Object retObject(Object objvalue);
// Java web method generated from WCF service WSDL
public Object retObject(
    Object objvalue);
}

The following illustrates why xsi:type is not preserved across an unmarshal/marshal operation.

A value of type uint is marshalled by WCF serialization mechanism as:
```
<objvalue xsi:type="xs:unsignedShort"/>
```
JAXB 2.0 unmarshaller unmarshals the value as an instance of int and assigns it to parameter objvalue.
The objvalue is marshalled back by JAXB 2.0 marshaller with an xsi:type of xs:int.
```
<objvalue xsi:type="xs:int"/>
```

One way to preserve and roundtrip the xsi:type is to use the mapSimpleTypeDef customization. The customization makes the mapping of XML Schema Part 2 datatypes one--to-one by generating additional Java classes. Thus, xs:unsignedShort will be bound to its own class rather than int, as shown:

//Java class to which xs:unsignedShort is bound
public class UnsignedShort { ... }

The following illustrates how the xsi:type is preserved across an unmarshal/marshal operation:

A value of type uint is marshalled by WCF serialization mechanism as:
```
<objvalue xsi:type="xs:unsignedShort"/>
```
JAXB 2.0 unmarshaller unmarshals the value as an instance of UnsignedShort and assigns it to parameter objvalue.
The objvalue is marshalled back by JAXB 2.0 marshaller with an xsi:type of xs:int.
```
<objvalue xsi:type="xs:unsignedShort"/>
```

Guideline: Use the mapSimpleTypedef customization where roundtripping of XML Schema types in Table 11–1 are used in xsi:type. However, it is preferable to avoid the use of CLR types listed in Table 11–1 since they are specific to .NET platform.

The syntax of the mapSimpleTypeDef customization is shown below.

<jaxb:bindings version="2.0"
               xmlns:jxb="http://java.sun.com/xml/ns/jaxb"
               xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <jaxb:bindings schemaLocation="schema-importedby-wcfsvcwsdl"
                   node="/xs:schema">
        <jaxb:globalBindings mapSimpleTypeDef="true"/>
    </jaxb:bindings>
    ....