Document Based WebServices

An interesting article Patterns and Strategies for Building Document-Based Web Services was posted on the Sun website which explains important aspects of developing document/literal web services.

The doc/lit encoding is important when it comes to interoperable web services as shown in the WS-I Basic Profile 1.0 and Attachments Profile Version 1.0. Although doc/lit is the preferred encoding most tookits don’t use it by default.

Recently I’ve tried to implement web service attachments in BEA Weblogic Server 8.1.SP3. Although it should work, it didn’t. The problem is that the ant tasks did not emit consistent type mapping descriptors and WSDL for the client and server side. At least on the same platform it should work but it doesn’t. That’s a humbling experience.

By now the easiest way to exchange binary data is still the base64binary schema type, which is larger on the wire but can be exchanged without trouble. If the caller of the service knows the mime type of the blob it’s possible to save it in an appropriate manner.

The following code snippet does the trick:

class Doc
{
byte[] blob;
String mimeType; // e.g. image/gif
}

class MyService
{
public Doc getDocument(){…};
}

By this you can exchange binary data of any type. At least until web service attachments work as expected on all major platforms.

To sum it up – if you have to be really interoperable with your web services you need a lot of knowledge about the underlying specs and technologies. The standard examples won’t help you very much.

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