Oracle SOA fault handling with ordered guaranteed delivery using BPEL, JMSAdapter, custom JMS headers, JMS message selectors, a JMS topic and durable subscribers

In this blog post I will demonstrate an error handling mechanism which can be used to achieve guaranteed delivery of messages in a specific order. To implement this I have used Oracle SOA Suite 11g, BPEL 2.0. The method described however can also be implemented by other technologies/languages. The method used is different from (as far as I know) previously described methods to implement exception handling in Oracle SOA Suite. A single JMS topic is used and JMS message selectors based on custom JMS headers are used by clients. By using a JMS topic, the services are loosely coupled. This method also allows tracing of flows over the topic in the Enterprise Manager Fusion Middleware Control (when Oracle SOA Suite is used). A screenshot of this mechanism implemented is shown in the screenshot below. It will be explained in more detail below.

JAXB and XML generation; missing elements

The Java API for XML Binding, JAXB (https://jaxb.java.net/) is a framework often used in Java to make working with XML easier. Most modern Java IDE's (such as JDeveloper, Eclipse, Netbeans) support direct generation of Java classes from an XML schema definition. JAXB allows Java code to be marshalled to XML and XML to be unmarshalled to Java classes.

If you generate Java classes from an XML schema definition, create an instance of the generated class and unmarshall it to XML, the XML will not in all cases be compliant to the schema the classes were generated from. This can cause problems if correctness is assumed based on usage of the framework. Validation can help detect problems and there are several methods to circumvent them.