This section gives an introduction to what a handler is and describes how you can write a synapse handler by walking you through a basic example.
Introduction to handlers
Handlers can be used to process requests in a scenario where you have multiple requests and each request needs be processed in a specific manner. A Handler defines the interface that is required to handle the request and concreteHandlers are to handle requests in a specific manner based on what needs to be done with regard to each type of request. The diagram below illustrates this.
Synapse handler is the interface used to register server response callbacks. Synapse handler provides the abstract handler implementation that executes the request in flow, request out flow, response in flow and response out flow.
The diagram below is an illustration of how the specified flows execute in the abstract handler implementation.
Request in flow
This executes when the request reaches the synapse engine.
Request out flow
This executes when the request goes out of the synapse engine.
Response in flow
This executes when the response reaches the synapse engine.
Response out flow
This executes when the response goes out of the synapse engine.
The diagram below illustrates the basic component structure of the ESB profile of WSO2 EI and how the flows mentioned above execute in the request path and the response path.
Now that you understand what a handler is, let's see how you can write a concrete Synapse handler.
Writing a concrete Synapse handler
The easiest way to write a concrete Synapse handler is to extend the
org.apache.synapse.AbstractSynapseHandler class. You can also write a concrete Synapse handler by implementing
org.apache.synapse.SynapseHandler, which is the SynapseHandler interface.
Following is an example Synapse handler implementation that extends the
Deploying the Synapse handler
To deploy your custom synapse handler in the ESB of WSO2 EI, bundle the artifact as a JAR file (with either the .jar or .xar format), and add it to the
<EI_HOME>/lib/ directory. Be sure to restart the server after adding the files.
Engaging the Synapse handler
To engage the deployed Synapse handler, you need to add the following configuration to the