Skip to main content

How to write a Synapse Handler for the WSO2 ESB ?


Synapse handler is new feature which come with the ESB 4.9.0. It provide abstract handler implementation to the users. User can create their own concrete handlers which is executing in the synapse layer. Main intention of this blog post is to explain how to write synapse handler and explain basic theoretical background.

1. What is the handler?

Handlers are basically talking with the chain of responsibility pattern. Chain of responsibility allows a number of classes to attempt to handle a request independently of any other object along the chain. Once the request is handled, it completes it's journey through the chain.
The Handler defines the interface which required to handle the request and concreteHandlers handle request in a specific manner that they are responsible for.




2. What is Synapse handler?

Synapse handler is providing abstract handle implementation which executes in the following four scenarios.





1. Request in flow
This is executing when request is hitting to the synapse engine.

public boolean handleRequestInFlow(MessageContext synCtx);

2. request out flow
This is executing when request goes out from the synapse engine. 

public boolean handleRequestOutFlow(MessageContext synCtx);

3. Response in flow
This is executing when response is hitting to the synapse engine.

public boolean handleResponseInFlow(MessageContext synCtx);

4. Response out flow
This is executing when response goes out from the synapse engine. 

public boolean handleResponseOutFlow(MessageContext synCtx);

Following diagram shows the basic component structure of the ESB and how above mentioned scenarios are executing in the request and response flow.





3. How to write concrete Synapse handler?

You can implement concrete handler by implementing SynapseHandler(org.apache.synapse.SynapseHandler) interface or can extends AbstractSynapseHandler(org.apache.synapse.AbstractSynapseHandler) class. 


public class TestHandler extends AbstractSynapseHandler {

    private static final Log log = LogFactory.getLog(TestHandler.class);

    @Override
    public boolean handleRequestInFlow(MessageContext synCtx) {
        log.info("Request In Flow");
        return true;
    }

    @Override
    public boolean handleRequestOutFlow(MessageContext synCtx) {
        log.info("Request Out Flow");
        return true;
    }

    @Override
    public boolean handleResponseInFlow(MessageContext synCtx) {
        log.info("Response In Flow");
        return true;
    }

    @Override
    public boolean handleResponseOutFlow(MessageContext synCtx) {
        log.info("Response Out Flow");
        return true;
    }
}


4. Configuration

You need to add following configuration item to the synapse-handler.xml(repository/conf) file to enable  deployed handler.

<handlers>
    <handler name="TestHandler" class="package.TestHandler"/>
</handlers>

5. Deployment

Handler can be deployed as a OSGI bundle or jar file to the ESB.


  
Labels:

Comments

Post a Comment

Popular posts from this blog

How to enable proxy service security in ESB 4.9.0?

Security is  one of the major concern when we developing API base integrations or application developments. WSO2 supports WS Security , WS-Policy and WS-Security Policy specifications. These specifications define a behavior model for web services. Proxy service security requirements are different from each others. WSO2 ESB providing pre-define commonly used twenty security scenarios to choose based on the security requirements. This functionality is provided by the security management feature which is bundled by default in service management feature in ESB. This configuration can be done via the web console until ESB 4.8.1 release, but this has been removed from the ESB 4.9.0. Even though this feature isn't provided by the ESB web console itself same functionality can be achieved by the new WSO2 Dev Studio . WSO2 always motivate to use dev studio to prepare required artifacts to the ESB rather than the web console. Better way to explain this scenario is by example. Following
3 comments
Read more

How to preserving HTTP headers in WSO2 ESB 4.9.0 ?

Preserving HTTP headers are important when executing backend services via applications/middleware. This is because most of the time certain important headers are removed or modified by the applications/middleware which run the communication. The previous version of our WSO2 ESB, version 4.8.1, only supported “ server ” and “ user agent ” header fields to preserve with, but with the new ESB 4.9.0, we’ve introduced a new new property ( http.headers.preserve ) for the passthru ( repository/conf/ passthru-http.properties ) and Nhttp( repository/conf/ nhttp.properties ) transporters to preserve more HTTP headers. Passthru transporter – support header fields               Location Keep-Alive Content-Length Content-Type Date Server User-Agent Host Nhttp transport – support headers Server User-Agent Date You can specify header fields which should be preserved in a comma-separated list, as shown below. http.headers.preserve = Location, Date, Server Note that
Post a Comment
Read more

How to monitor the Thread CPU usage in the WSO2 Products?

1. Download JConsole topthreads Plugin. 2. Add following entries to the PRODUCT_HOME/bin/wso2server.sh     -Dcom.sun.management.jmxremote \     -Dcom.sun.management.jmxremote.port=PORT \     -Dcom.sun.management.jmxremote.ssl=false \     -Dcom.sun.management.jmxremote.authenticate=false \     -Djava.rmi.server.hostname=IP_ADDRESS \ Define your IP_ADDRESS address and PORT (port should be not used anywhere in that instance) 3. Run the JConsole using following command.     jconsole -pluginpath PATH_TO_JAR/topthreads-1.1.jar 4. Copy "JMXServerManager JMX Service URL" from the wso2carbon logs after restart the Wso2 Server (Eg:- service:jmx:rmi://localhost:11111/jndi/rmi://localhost:9999/jmxrmi) to the Remote process with the username and password. 5. Under Top Threads tab you can monitor the thread CPU usage.
1 comment
Read more