Transforming API Message Payload¶
When a request comes to the API Manager, it sends the response in the same format of the request. For example, the API Manager handles JSON to JSON transformations out of the box. If the backend does not accept messages of the same content type of the request message, it must be transformed to a different format. The API Gateway of the API Manager handles these transformations using message builders and formatters.
When a message comes in to the API Gateway, the receiving transport selects a message builder based on the message's content type. It uses that builder to process the message's raw payload data and convert it into JSON. Conversely, when sending a message out from the Gateway, a message formatter is used to build the outgoing stream from the message. As with message builders, the message formatter is selected based on the message's content type.
Tip
Note that if you edit an API's synapse configuration as mentioned in this guide and then go back to the API Publisher and save the API, your changes will be overwritten. Therefore, we do not recommend changing the API's synapse configuration directly. The recommended way to extend an API's mediation flow is by attaching policies to API operations.
Info
Also see the following sections in the documentation. The integration runtime is used to implement the API Gateway through which API messages are transformed:
JSON message builders and formatters¶
There are two types of message builders and formatters for JSON. The default builder and formatter keep the JSON representation intact without converting it to XML. You can access the payload content using the JSON Path or XPath and convert the payload to XML at any point in the mediation flow.
-
org.apache.synapse.commons.json.JsonStreamBuilder
-
org.apache.synapse.commons.json.JsonStreamFormatter
If you want to convert the JSON representation to XML before the mediation flow begins, use the following builder and
formatter instead.
Note that some data loss can occur during the JSON -> XML -> JSON conversion process.
-
org.apache.synapse.commons.json.JsonBuilder
-
org.apache.synapse.commons.json.JsonFormatter
The builders and formatters are configured respectively in the messageBuilders
and messageFormatters
sections of
the Axis2 configuration files located in the <APIM_HOME>/repository/conf/axis2
directory. Both types of JSON
builders use StAXON as the underlying JSON processor.
The following builders and formatters are also included for compatibility with older API Manager versions:
org.apache.axis2.json.JSONBuilder/JSONMessageFormatter
org.apache.synapse.commons.json.JsonStreamBuilder/JSONStreamFormatter
org.apache.axis2.json.JSONBadgerfishOMBuilder/JSONBadgerfishMessageFormatter
Note
Always use the same type of builder and formatter combination. Mixing different builders and formatters will cause errors at runtime.
If you want to handle JSON payloads that are sent using a media type other than application/json
, you must
register the JSON builder and formatter for that media type using the deployment.toml
file found in the
<APIM_HOME>/repository/conf
directory):
For example, if the media type is text/javascript
, register the message builder and formatter as follows:
[message_builder]
text_javascript = "org.apache.synapse.commons.json.JsonStreamBuilder"
[message_formatter]
text_javascript = "org.apache.synapse.commons.json.JsonStreamFormatter"
Tip
To support having spaces inside JSON attributes, change the default JSON builder and formatter to the following
pair to the <APIM_HOME>/repository/conf/deployment.toml
file:
Tip
To support use cases for JSON payloads with arrays, change the default JSON builder and formatter to the following
pair to the <APIM_HOME>/repository/conf/deployment.toml
file:
[message_builder]
application_json = "org.apache.synapse.commons.json.JsonStreamBuilder"
[message_formatter]
application_json = "org.apache.synapse.commons.json.JsonStreamFormatter"
Else, in JSON to XML conversion, there might be issues as below:
JSON
Converted XML
Note
When you modify the builders/formatters in Axis2 configuration, make sure that you have enabled only one correct message builder/formatter pair for a given media type.
XML representation of JSON payloads¶
When building the XML tree, JSON builders attach the converted XML infoset to a special XML element that acts as
the root element of the final XML tree. If the original JSON payload is of type object
, the special element is
<jsonObject/>
. If it is an array
, the special element is <jsonArray/>
. Following are examples of JSON and
XML representations of various objects and arrays.
Null objects¶
JSON:
XML:
Empty objects¶
JSON:
XML:
Empty strings¶
JSON:
XML:
Empty array¶
JSON:
XML (JsonStreamBuilder):
XML (JsonBuilder):
Named arrays¶
JSON:
XML (JsonStreamBuilder):
XML (JsonBuilder):
JSON:
XML (JsonStreamBuilder):
XML (JsonBuilder):
Anonymous arrays¶
JSON:
XML (JsonStreamBuilder):
XML (JsonBuilder):
<jsonArray>
<?xml-multiple jsonElement?>
<jsonElement>1</jsonElement>
<jsonElement>2</jsonElement>
</jsonArray>
JSON:
XML (JsonStreamBuilder):
<jsonArray>
<jsonElement>1</jsonElement>
<jsonElement>
<jsonArray></jsonArray>
</jsonElement>
</jsonArray>
XML (JsonBuilder):
<jsonArray>
<?xml-multiple jsonElement?>
<jsonElement>1</jsonElement>
<jsonElement>
<jsonArray>
<?xml-multiple jsonElement?>
</jsonArray>
</jsonElement>
</jsonArray>
XML processing instructions (PIs)¶
Note that the addition of xml-multiple
processing instructions to the XML payloads whose JSON representations contain
arrays. JsonBuilder
(via StAXON) adds these instructions to the XML payload that it builds during the JSON to XML
conversion so that during the XML to JSON conversion, JsonFormatter
can reconstruct the arrays that are present in
the original JSON payload. JsonFormatter
interprets the elements immediately following a processing instruction to
construct an array.
Special characters¶
When building XML elements, the ‘$’ character and digits are handled in a special manner when they appear as the
first character of a JSON key. Following are examples of two such occurrences. Note the addition of the
_JsonReader_PS_
and _JsonReader_PD_
prefixes in place of the ‘$’ and digit characters, respectively.
JSON:
XML:
JSON:
XML:
Converting a payload between XML and JSON¶
To convert an XML payload to JSON, set the messageType
property to application/json
in the axis2 scope before
sending message to an endpoint. Similarly, to convert a JSON payload to XML, set the messageType
property to
application/xml
or text/xml
. For example:
<?xml version="1.0" encoding="UTF-8"?>
<api name="admin--TOJSON" context="/tojson" version="1.0" version-type="url">
<resource methods="POST GET DELETE OPTIONS PUT" url-mapping="/*">
<inSequence>
<property name="POST_TO_URI" value="true" scope="axis2" />
<property name="messageType" value="application/json" scope="axis2" />
<filter source="$ctx:AM_KEY_TYPE" regex="PRODUCTION">
<then>
<send>
<endpoint name="admin--Test_APIproductionEndpoint_0">
<http uri-template="http://localhost:9767/services/StudentService">
<timeout>
<duration>30000</duration>
<responseAction>fault</responseAction>
</timeout>
<suspendOnFailure>
<errorCodes>-1</errorCodes>
<initialDuration>0</initialDuration>
<progressionFactor>1.0</progressionFactor>
<maximumDuration>0</maximumDuration>
</suspendOnFailure>
<markForSuspension>
<errorCodes>-1</errorCodes>
</markForSuspension>
</http>
</endpoint>
</send>
</then>
<else>
<sequence key="_sandbox_key_error_" />
</else>
</filter>
</inSequence>
<outSequence>
<send />
</outSequence>
</resource>
<handlers>
<handler class="org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler" />
<handler class="org.wso2.carbon.apimgt.gateway.handlers.throttling.APIThrottleHandler">
<property name="id" value="A" />
<property name="policyKey" value="gov:/apimgt/applicationdata/tiers.xml" />
</handler>
<handler class="org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageHandler" />
<handler class="org.wso2.carbon.apimgt.usage.publisher.APIMgtGoogleAnalyticsTrackingHandler" />
<handler class="org.wso2.carbon.apimgt.gateway.handlers.ext.APIManagerExtensionHandler" />
</handlers>
</api>
An example command to invoke above API:
curl -v -X POST -H "Content-Type:application/xml" -H "Authorization: Bearer xxx" [email protected] "http://10.100.1.110:8280/tojson/1.0"
If the request payload is as follows:
<?xml version="1.0" encoding="UTF-8"?>
<coordinates>
<location>
<name>Bermuda Triangle</name>
<n>25.0000</n>
<w>71.0000</w>
</location>
<location>
<name>Eiffel Tower</name>
<n>48.8582</n>
<e>2.2945</e>
</location>
</coordinates>
The response payload will look like this:
{
"coordinates":{
"location":[
{
"name":"Bermuda Triangle",
"n":25.0000,
"w":71.0000
},
{
"name":"Eiffel Tower",
"n":48.8582,
"e":2.2945
}
]
}
}
Note that we have used the Property mediator to mark the outgoing payload to be formatted as JSON. For more information about the Property Mediator, see the Property Mediator page.
Similarly if the response message needs to be transformed, set the messageType property in the outSequence.
<?xml version="1.0" encoding="UTF-8"?>
<api name="admin--TOJSON" context="/tojson" version="1.0" version-type="url">
<resource methods="POST GET DELETE OPTIONS PUT" url-mapping="/*">
<inSequence>
<property name="POST_TO_URI" value="true" scope="axis2" />
<filter source="$ctx:AM_KEY_TYPE" regex="PRODUCTION">
<then>
<send>
<endpoint name="admin--Test_APIproductionEndpoint_0">
<http uri-template="http://localhost:9767/services/StudentService">
<timeout>
<duration>30000</duration>
<responseAction>fault</responseAction>
</timeout>
<suspendOnFailure>
<errorCodes>-1</errorCodes>
<initialDuration>0</initialDuration>
<progressionFactor>1.0</progressionFactor>
<maximumDuration>0</maximumDuration>
</suspendOnFailure>
<markForSuspension>
<errorCodes>-1</errorCodes>
</markForSuspension>
</http>
</endpoint>
</send>
</then>
<else>
<sequence key="_sandbox_key_error_" />
</else>
</filter>
</inSequence>
<outSequence>
<property name="messageType" value="application/json" scope="axis2" />
<send />
</outSequence>
</resource>
<handlers>
<handler class="org.wso2.carbon.apimgt.gateway.handlers.security.APIAuthenticationHandler" />
<handler class="org.wso2.carbon.apimgt.gateway.handlers.throttling.APIThrottleHandler">
<property name="id" value="A" />
<property name="policyKey" value="gov:/apimgt/applicationdata/tiers.xml" />
</handler>
<handler class="org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageHandler" />
<handler class="org.wso2.carbon.apimgt.usage.publisher.APIMgtGoogleAnalyticsTrackingHandler" />
<handler class="org.wso2.carbon.apimgt.gateway.handlers.ext.APIManagerExtensionHandler" />
</handlers>
</api>
Info
XML to JSON Transformation Parameters
See JSON Transformation Parameters
for additional parameters for converting XML to JSON.