mediation-sequence.xml

<?xml version="1.0" encoding="UTF-8"?>

<sequence name="size-limit-mediation" 
    xmlns="http://ws.apache.org/ns/synapse">

    <!-- defining the payload size limit class mediator in the sequence with the respective size limit in MB unit -->
    <!-- the class mediator will return a boolean value with the property named "payload-size-too-large" to specify whether the message    is too large or not -->
    <class name="com.sample.mediator.PayloadSizeLimitMediator">
        <!-- the size limit has been configured to 10MB limit, change this according to your requirement -->
        <property name="sizeLimit" value="10" />
        <!-- specifying the API name. You can use either $ctx:API_NAME or $ctx:SYNAPSE_REST_API -->
        <property name="apiName" expression="$ctx:API_NAME" />
        <!-- specify the direction flow of the execution whether in flow or out flow -->
        <property name="flowDirection" value="In flow" />
    </class>

    <!-- a custom log mediator to log the property returned by class mediator -->
    <log level="custom">
        <property name="is-payload-larger" expression="get-property('payload-size-too-large')" />
    </log>

    <!-- filter and send a custom error response based on the class mediator output property -->
    <!-- if the property 'payload-size-too-large' is set to true means, that the payload size is larger than the defined value -->
    <filter source="get-property('payload-size-too-large')" regex="true">
        <then>
            <!-- a custom log mediator -->
            <log level="custom">
                <property name="message" value="The payload size is larger than the specified limit" />
            </log>

            <!-- payload factory mediator to specify custom response -->
            <payloadFactory media-type="json">
                <format>                    
                    {                        
                        "status": $1,                        
                        "message": "$2"                    
                    }                
                </format>
                <args>
                    <arg value="413" />
                    <arg value="payload is too large" />
                </args>
            </payloadFactory>

            <!-- change the HTTP status code. Below is set to 400 status code -->
            <property name="HTTP_SC" value="413" scope="axis2" />
            <!-- response back to the client with application/json format -->
            <property name="messageType" value="application/json" scope="axis2" />

            <!-- respond back to the client if the payload size is too large with the above-mentioned custom response -->
            <respond />
        </then>
        <else>
            <!-- a custom log mediator to log the flow -->
            <log level="custom">
                <property name="message" value="The payload size is not larger than specified limit" />
            </log>
        </else>
    </filter>

</sequence>