This documentation is for WSO2 Enterprise Integrator version 6.0.0 . View documentation for the latest release in the 6.x.x family and the latest release in the 7.x.x family.

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A mediator is a full-powered processing unit in the EI. At run-time, a mediator has access to all the parts of the EI 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 EI 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 EI. You can write a custom mediator and add it to the EI. 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 EI 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 EI mediator catalog





CallInvoke 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 EI


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

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 EI

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

BuilderBuilds the actual SOAP message, from a message, which is coming into the ESB profile through the Binary Relay. 


Evaluates user actions against a XACML policy


2-legged OAuth support

SmooksUsed to apply lightweight transformations on messages in an efficient manner.
Data MapperConverts and transforms one data format to another, or changes the structure of the data in a message. 

BeanManipulates 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
Publish EventConstructs events and publishes them to different systems such as WSO2 BAM/DAS/CEP/SP via event sinks.
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