Data binding

Data binding

Data binding is the key for any web service development. Data binding means 

mapping between Java objects and XML elements. As we know, with web service, 

messages are exchanged as XML artifacts. So there has to be some way to convert 

these XML into Java objects and vice versa for the application to process as service 

and client. Data binding components perform this mapping for you. CXF supports 

two types of data binding components—JAXB and Aegis. CXF uses JAXB as the 

default data binding component. As a developer, you have the choice of specifying 

the binding discipline through a configuration file or API. If no binding is specified, 

then JAXB is taken as a default binding discipline. The latest version of CXF uses 

JAXB 2.1. JAXB uses annotations to define the mapping between Java objects and 

XML. The following code illustrates the use of JAXB annotations:

 

@XmlRootElement(name="processOrder", namespace=" http://localhost/ 

                      orderprocess")

@XmlAccessorType(XmlAccessType.FIELD)

@XmlType(name="processOrder", namespace= 

              " http://localhost/orderprocess")

public class OrderProcess {

    @XmlElement(name="arg0", namespace="")

    private order.Order arg0;

   //Gettter and Setter 

….

 

}

As shown in the previous code, the @Xml specific annotations represents the JAXB 

metadata that is used by JAXB to map Java classes to XML schema constructs. For 

example, the @XmlType annotation specifies that the OrderProcess class will be 

mapped to complex XSD element type 'processOrder' that contains an element 

'arg0' of type 'Order' bean.

 

CXF also supports the Aegis data binding component to map between Java objects 

and XML. Aegis allows developers to gain control of data binding through its 

flexible mapping system. You do not have to rely on annotations to devise the 

mapping. Your Java code is clean and simple POJO. 

 

Aegis also supports some annotations that can be used to devise binding. Some of 

the annotations that can be used with Aegis are:

• XmlAttribute

• XmlElement

• XmlParamType

• XmlReturnType

• XmlType

 

In Aegis, you define the data mapping in a file called  <MyJavaObject>.aegis.xml, 

where MyJavaObject is the object that you are trying to map with XML. Aegis reads 

this XML to perform the necessary binding. Aegis also uses reflection to derive the 

mapping between Java object and XML. The following code fragment shows the 

sample Aegis mapping file: 

<?xml version="1.0" encoding="UTF-8"?>

<mappings>

    <mapping name="HelloWorld">

        <method name="sayHi">

            <parameter index="0" mappedName= 

                             "greeting" nillable='false' />

        </method>

    </mapping>

</mappings>

The above XML fragment states that a string parameter of a method named sayHi of 

the bean HelloWorld should be mapped to a name as greeting.

 

You can configure your web service to use Aegis data binding as follows:

<jaxws:endpoint id="orderProcess" implementor="demo.order.

OrderProcessImpl" address="/OrderProcess" >

   <jaxws:dataBinding>

    <bean class="org.apache.cxf.aegis.databinding.AegisDatabinding" />

   </jaxws:dataBinding>

</jaxws:endpoint>