This documentation is for WSO2 Enterprise Service Bus version 5.0.0. View documentation for the latest ESB.
Skip to end of metadata
Go to start of metadata

A mediator is a full-powered processing unit in the ESB. At run-time, a mediator has access to all the parts of the ESB along with the current message and can do virtually anything with the message.

When adding a mediator to a sequence , you can configure the mediator in design view or in source view. Source view provides the XML representation of the configurations done in the UI. When you edit the source XML all changes immediately reflect in the design view as well.

Each mediator has its own XML configuration. In the source view of the following mediators, you can comment out required lines if necessary when you edit the XML.

  • Aggregate Mediator
  • Cache Mediator
  • Filter Mediator
  • In Mediator
  • Iterate Mediator
  • Out Mediator
  • Sequence Mediator
  • Synapse Mediator
  • Template Mediator
  • Validate Mediator

It is also possible to comment out required lines in the Synapse definition as well as in the source view of the complete ESB configuration.

Mediators in a sequence can be one of the following types:

  • Node mediators - Contains child mediators.
  • Leaf mediators - Does not hold any other child mediators.

The message content is accessed by some mediators in some mediation scenarios while it is not accessed in the other scenarios. Mediators can be classified as follows based on this aspect.

  • Content-aware mediators: These mediators always access the message content when mediating messages (e.g., Enrich mediator).
  • Content-unaware mediators: These mediators never access the message content when mediating messages (e.g., Send mediator).
  • Conditionally content-aware mediators: These mediators could be either content-aware or content-unaware depending on their exact instance configuration. For an example a simple Log Mediator instance (i.e. configured as <log/>) is content-unaware. However a log mediator configured as <log level=”full”/> would be content-aware since it is expected to log the message payload.

Mediators are considered to be one of the main mechanisms for extending an ESB. You can write a custom mediator and add it to the ESB. This custom mediator and any other built-in mediator will be exactly the same as the API and the privileges.

The standard mediators in WSO2 ESB are listed in the table below. Click a link for details on that mediator. There are also many samples that demonstrate how to use mediators.

The WSO2 ESB mediator catalog




CoreCallInvoke a service in non blocking synchronous manner
 EnqueueUses a priority executor to ensure high-priority messages are not dropped



Sends a message



Moves the message from the In flow to the Out flow, skipping all remaining configuration in the In flow



Inserts a reference to a sequence

 RespondStops processing on the message and sends it back to the client

Sends event notifications to an event source, publishes messages to predefined topics



Drops a message

 Call TemplateConstructs a sequence by passing values into a sequence template



Enriches a message



Sets or remove properties associated with the message



Logs a message



Filters a message using XPath, if-else kind of logic



Applies to messages that are in the Out path of the ESB



Applies to messages that are in the In path of the ESB

 ValidateValidates XML messages against a specified schema.



Filters messages using XPath, switch logic



Routes messages based on XPath filtering


Conditional Router

Implements complex routing rules (Header based routing, content based routing and other rules)



Performs XSLT transformations on the XML payload

 FastXSLTPerforms XSLT transformations on the message stream



Modifies and rewrites URLs or URL fragments


XQueryPerforms XQuery transformation



Sets or removes SOAP headers


Fault (also called Makefault)

Create SOAP Faults

 PayloadFactoryTransforms or replaces message content in between the client and the backend server



Evaluates messages based on whether the same message came to the ESB

 ForEachSplits a message into a number of different messages by finding matching elements in an XPath expression of the original message.



Clones a message



Stores messages in a predefined message store



Splits a message



Combines a message



Blocks web services calls



Executes a set of mediators transactionally



Limits the number of messages



Writes data to database



Retrieves information from database

 EJBCalls an external Enterprise JavaBean(EJB) and stores the result in the message payload or in a message context property.



Executes rules



Evaluates user actions against a XACML policy



2-legged OAuth support

 SmooksUsed to apply lightweight transformations on messages in an efficient manner.
ExtensionBeanManipulates JavaBeans



Creates and executes a custom mediator



Executes a custom command



Executes a mediator written in Scripting language



Creates a mediator managed by Spring

AgentBAMCaptures data events and sends them to the BAM server
  • No labels