kXML-RPC Enables Service-Oriented Mobile Computing : Page 3

...
     <param>
         <value><i4>2</i4></value>
      </param>
      <param>
         <value><i4>3</i4></value>
      </param>
...

The XML-RPC clients and servers encode the data in this way, and they must map them to the appropriate equivalent platform datatype implementation. In kXML-RPC, the XML-RPC datatypes are mapped to the Java 1.3-compliant datatypes shown in Table 2.

<i4>263</i4>

<boolean>0</boolean>

<string>I got no time for the jibba-jabba.</string>

<dateTime.iso8601>
    20070828T14:08:55
</dateTime.iso8601>

<base64>
     eW91IGNhbid0I
</base64>

<struct>
  <member>
    <name>name</name>
    <value>
      <string>Dave</string>
    </value>
  </member>
  <member>
    <name>age</name>
    <value>
      <i4>28</i4>
    </value>
  </member>
</struct>

<array>
  <data>
    <value>
      <i4>13</i4>
    </value>
     <value>
      <string>Foo you!</string>
    </value>
    <value>
      <boolean>1</boolean>
    </value>
  </data>
</array>

The integers and boolean values do not map to int and bool primitives, but to their respective class equivalents. kXML-RPC is designed as such so that these kinds of values can be added to Vectors and Hashtables, because this is how the XML-RPC Struct and Array types are mapped respectively. Also note that when tags are not used to specify a type, the type is assumed to be a String.

kXML-RPC utilizes the kXML parser and serializer to create outgoing messages and process incoming messages. The XmlRpcClient class delegates serialization and parsing to the XmlRpcWriter and XmlRpcParser classes. Figure 1 illustrates the flow of control when the execute method of XmlRpcClient is called.

The XmlRpcWriter class creates the XML-RPC message and uses an HTTP POST request to send the message to a web service. The payload of the HTTP response is then processed by the XmlRpcParser, where the resulting object is finally returned by the execute method.

XML-RPC Limitations
XML-RPC provides a simple, minimalist XML grammar for invoking service operations. It does not, however, lend itself well to more advanced scenarios. Securing XML-RPC messages is limited to Transport Level Security (TLS) or ad-hoc XML encryption. Additionally, the protocol provides no extension mechanism to facilitate exchange of security tokens, transaction semantics, conversational state, endpoint addressing, intermediary handling, or other enterprise-grade messaging capabilities. If these more sophisticated capabilities are a part of your system requirements, then XML-RPC is not the answer. If, however, you're looking for a quick, streamlined means of exchanging simple data structures between two systems in a neutral fashion, then XML-RPC is just right.

SOA Goes Wireless
As SOA continues to become a more pervasive factor within enterprise information systems, its convergence with mobile computing is inevitable. Service orientation is going wireless; it's simply a matter of how much and how soon. When this occurs, enterprises will need to evaluate their requirements and make a determination regarding the right messaging protocol. XML-RPC and the kXML-RPC library certainly are in the mix.