This sample demonstrates how to specify a fault sequence with a regular mediation sequence. Here a message is sent from the sample client to the back-end service through the ESB via 3 mediation options which are a success scenario, a failure scenario without error handling and a failure scenario with proper error handling.
For a list of prerequisites, see Prerequisites to Start the ESB Samples.
Building the sample
The XML configuration for this sample is as follows:
This configuration file
synapse_sample_4.xml is available in the
To build the sample
Start the ESB with the sample 4 configuration. For instructions on starting a sample ESB configuration, see Starting the ESB with a sample configuration.
The operation log keeps running until the server starts, which usually takes several seconds. Wait until the server has fully booted up and displays a message similar to "WSO2 Carbon started in n seconds."
Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.
Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.
Now you have a running ESB instance and a back-end service deployed. In the next section, we will send a message to the back-end service through the ESB using a sample client.
Executing the sample
The sample client used here is the Stock Quote Client, which can operate in several modes. For further details on this sample client and its operation modes, see Stock Quote Client.
To execute the sample client
Run each of the following commands from the
<ESB_HOME>/samples/axis2Clientdirectory to trigger sample messages to the back-end service.
Analyzing the output
When the IBM stock quote is requested, the configuration routes it to the defined inline , which then routes the message to the
SimpleStockQuoteService on the local Axis2 instance. Therefore, a valid response message is shown at the client.
When the MSFT stock quote is requested, the ESB is instructed to route the message to the endpoint defined as the bogus endpoint, which does not exist. This triggers a fault scenario.
The ESB executes the specified error handler sequence closest to the point where the error was encountered. In this case, the currently-executing sequence is main and it does not specify an
onError attribute. Whenever ESB cannot find an error handler, it looks for a sequence named fault. As a result, the fault sequence starts executing and it writes a generic error message to the log.
When the SUN stock quote is requested, it invokes the sunSequence custom sequence which specifies
sunErrorHandler as the error handler as you can see in the
When the send fails, you will see a proper error handler invocation and the custom error message that is printed as follows.