You can send API messages through the API Manager without any transformation configurations, if the back-end accepts messages of the same format. For example, the API Manager handles JSON to JSON transformations out of the box. In cases where the back-end does not accept the same format, the transformations are done as described below:
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.
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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. As a result, we do not recommend changing the API's synapse configuration directly. The recommended way to extend an API's mediation flow is by engaging In/Out sequences. |
Also see the following sections in the WSO2 ESB documentation. WSO2 ESB is used to implement the API Gateway through which API messages are transformed:
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.
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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 to -> XML to -> 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 , respectively, of the Axis2 configuration files located in the <PRODUCT_HOME>/repository/conf/axis2 directory. Both types of JSON builders use StAXON as the underlying JSON processor.
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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. |
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.
JSON:
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{"object":null} |
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<jsonObject>
<object></object>
</jsonObject> |
JSON:
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<jsonObject>
<object></object>
</jsonObject> |
JSON:
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<jsonObject>
<object></object>
</jsonObject> |
JSON:
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<jsonArray>
<?xml-multiple jsonElement?>
</jsonArray> |
JSON:
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{"array":[1,2]} |
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<jsonObject>
<?xml-multiple array?>
</jsonObject> |
JSON:
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<jsonArray>
<?xml-multiple jsonElement?>
<jsonElement>1</jsonElement>
<jsonElement>
<jsonArray>
<?xml-multiple jsonElement?>
</jsonArray>
</jsonElement>
</jsonArray> |
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.
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.
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<jsonObject>
<_JsonReader_PD_32X32>image_32x32.png</_JsonReader_PD_32X32>
</jsonObject> |
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:
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