This section introduces handlers and using an example, explains how to write a custom handler:
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When an API is created, a file with its synapse configuration is added to the API Gateway. You can find it in the
<APIM_HOME>/repository/deployment/server/synapse-configs/default/api folder. It has a set of handlers, each of which is executed on the APIs in the same order they appear in the configuration. You find the default handlers in any API's Synapse definition as shown below.
APIAuthenticationHandler:Validates the OAuth2 bearer token used to invoke the API. It also determines whether the token is of type
MessageContextvariables as appropriate.
APIThrottleHandler:Throttles requests based on the throttling policy specified by the
policyKeyproperty. Throttling is applied both at the application level as well as subscription level.
APIMgtUsageHandler:Publishes events to WSO2 Data Analytics Server (WSO2 DAS) for collection and analysis of statistics. This handler only comes to effect if . See Working with Statistics for more information.
APIMgtGoogleAnalyticsTrackingHandler:Publishes events to Google Analytics. This handler only comes into effect if Google analytics tracking is enabled. See for more information.
APIManagerExtensionHandler: Triggers extension sequences. By default, the extension handler is listed at last in the handler chain, and therefore is executed last. You cannot change the order in which the handlers are executed, except the extension handler. To configure the API Gateway to execute extension handler first, uncomment the
<ExtensionHandlerPosition>section in the
<APIM_HOME>/repository/conf/api-manager.xmlfile and provide the value
top. This is useful when you want to execute your own extensions before our default handlers in situations like doing additional security checks such as signature verification on access tokens before executing the default security handler.
See Adding Mediation Extensions.
Prior to Message logging is handled by
APIManagerExtensionHandler for API Manager 1.9.1 version, this message logging is handled by
APIManagerExtensionHandlerand above. Addition to the above mentioned Handlers,
APILogMessageHandler has introduced from API Manager version 1.9.1 onwards
APILogMessageHandler has introducedonwards.
APILogMessageHandler is a sample handler that comes with WSO2 API Manager that can be used for logging.
Why are logs have removed from
The primary purpose of
For example, When the
Inorder In order to enable logging by invoking invoking
APILogMessageHandler, follow the steps below steps.
To enable Message Logging per API :
Open the synapse Configuration of the API located in
<APIM_HOME>/repository/deployment/server/synapse-configs/default/apidirectory and add below handler before before
Copy the following code into the <APIMthe
<APIM_HOME>/repository/conf/log4j.propertiesfile to file to enable printing DEBUG logs.
log4j.logger.org.wso2.carbon.apimgt.gateway.handlers.logging.APILogMessageHandler = DEBUG
Restart API Manager server.
To enable Message Logging into APIS created from publisher automatically :
Open velocity_template.xml file located in the <APIM_HOME>/repository/resources/api_templates directory and /velocity_template.xml file and copy the following handler beofore </handlers>Handlers>.
- Restart API Manager server.
Writing a custom handler
The outcome of using a Class Mediator vs. a Synapse Handler are very similar. However, when using a custom handler you need to maintain a customized velocity template file that needs to be manually merged when you upgrade your product to a newer version. Therefore, it is recommended to use custom Handlers when you wish to specify the exact order of execution of JARs as this can not be done with Mediators.