The Builder Mediator can be used to build the actual SOAP message from a message coming in to ESB through the Binary Relay. One usage is to use this before trying to log the actual message in case of an error. Also with the Builder Mediator ESB can be configured to build some of the messages while passing the others along.
In order to build a message using the Builder mediator, BinaryRealyBuilder should be specified as the message builder in <ESB_HOME>/repository/conf/axis2/axis2.xml file for the content type of the message. Also, the message formatter of the content type should be ExpandingMessageFormatter in the same file. It is not possible to use it as an alternative way of engaging builders/formaters to the the message flow bypassing global axis2.xml.
By default, Builder Mediator uses the axis2 default Message builders for the content types. User can override those by using the optional messageBuilder configuration. For more information, see Working with Message Builders and Formatters.
Like in axis2.xml user has to specify the content type and the implementation class of the messageBuilder. Also user can specify the message formatter for this content type. This is used by the ExpandingMessageFormatter to format the message before sending to the destination.
Syntax
<syn:builder xmlns:syn="http://ws.apache.org/ns/synapse">
<syn:messageBuilder contentType="" class="" [formatterClass=""]/>
</syn:builder>