I am working on a WSO2 ESB project and I have some doubts about how to correctly handle the fault situation.
So for example I have this API:
<?xml version="1.0" encoding="UTF-8"?>
<api context="/weather/crop_calendar" name="crop_calendar" xmlns="http://ws.apache.org/ns/synapse">
<resource methods="GET" uri-template="/country/{countryId}/crops?lang={lang_id}">
<inSequence>
<log level="full"/>
<property expression="get-property('uri.var.countryId')" name="countryId" scope="default" type="STRING"/>
<property expression="$url:lang" name="langId" scope="default" type="STRING"/>
<log level="custom">
<property expression="$ctx:countryId" name="countryId"/>
<property expression="$ctx:langId" name="langId"/>
</log>
<property name="messageType" scope="axis2" type="STRING" value="application/xml"/>
<payloadFactory media-type="xml">
<format>
<ds:GetCropCalendarCommoditiesList xmlns:ds="http://ws.wso2.org/dataservice">
<country_id>$1</country_id>
<ds:language_id>$2</ds:language_id>
</ds:GetCropCalendarCommoditiesList>
</format>
<args>
<arg evaluator="xml" expression="$ctx:countryId"/>
<arg evaluator="xml" expression="$ctx:langId"/>
</args>
</payloadFactory>
<header name="Action" scope="default" value="urn:SelectCropCalendarCommoditiesList"/>
<call>
<endpoint key="cropCalendarEndpoint"/>
</call>
<property name="messageType" scope="axis2" type="STRING" value="application/json"/>
<property expression="json-eval($.)" name="JSONPayload" scope="default" type="STRING"/>
<script language="js"><![CDATA[var log = mc.getServiceLog();
function scan(obj) {
var k;
if (obj instanceof Object) {
for (k in obj){
if (obj.hasOwnProperty(k)){
obj[k] = checkForNull(obj[k]);
//recursive call to scan property
scan(obj[k]);
}
}
} else {
//not an Object so obj[k] here is a value
}
}
function checkForNull(value) {
if (value instanceof Object && "@nil" in value) {
return null;
}
return value;
}
log.info("----------------------------- CROP CALENDARD COMMODITIS LISTING SCRIPT START ------------------------------------------------");
var lang_id = mc.getProperty('langId');
// stange workaround for getting JSON Payload. getPayloadJSON returned null.
var pl_string = mc.getProperty("JSONPayload");
log.info("PAYLOAD STRING: " + pl_string);
var payload = JSON.parse(pl_string);
// Create new response:
var response = payload;
log.info("RESPONSE: " + JSON.stringify(response));
scan(response);
// Fix the single element problem:
if (!(response.CropCalendarCommodities.CommoditiesList instanceof Array)) {
log.info("It is not an array, convert it into an array");
singleCommodity = response.CropCalendarCommodities.CommoditiesList;
response.CropCalendarCommodities.CommoditiesList = [];
response.CropCalendarCommodities.CommoditiesList.push(singleCommodity);
}
// Convert array of crops into required HATEOS format
var cropsList = new Array();
for (i = 0; i < response.CropCalendarCommodities.CommoditiesList.length; i++) {
log.info("Crop: " + i + " CROP NAME: " + response.CropCalendarCommodities.CommoditiesList[i].commodity_name);
commodityCropCalendarDetailsLinks = [];
commodityCropCalendarDetailsRefObj = {};
commodityCropCalendarDetailsRefObj.rel = "commodity_enutrifood_details";
commodityCropCalendarDetailsRefObj.href = "http://5.249.148.180:8280/weather/crop_calendar/commodity/" + checkForNull(response.CropCalendarCommodities.CommoditiesList[i].commodity_id) + "?lang=" + lang_id;
commodityCropCalendarDetailsRefObj.type = "GET";
commodityCropCalendarDetailsLinks.push(commodityCropCalendarDetailsRefObj);
response.CropCalendarCommodities.CommoditiesList[i].links = commodityCropCalendarDetailsLinks;
}
log.info("----------------------------- CROP CALENDARD COMMODITIS LISTING SCRIPT END ------------------------------------------------");
// put payload back
mc.setPayloadJSON(response);]]></script>
<property name="RESPONSE" scope="default" type="STRING" value="true"/>
<header action="remove" name="To" scope="default"/>
<send/>
</inSequence>
<outSequence/>
<faultSequence>
// HERE HANDLE THE ERROR CASES
</faultSequence>
</resource>
</api>
This API take 2 input parameters in the URL:
and uses both to perform a DSS query, then the query output is converted in a JSON document and then Script mediator process this JSON document.
Error can take place during this mediators chain.
For example passing a countryId related to a country so there are no data in the database, the DSS query return something like this (after thge JSON conversion):
{"CropCalendarCommodities":null}
The problem is that when this document is processed by the Script mediator, WSO2 go into error because can't access to this element into the previous JSON:
CropCalendarCommodities.CommoditiesList
and I am obtaining an error like this:
TID: [-1234] [] [2018-06-13 10:26:58,527] ERROR {org.apache.synapse.mediators.bsf.ScriptMediator} - The script engine returned an error executing the inlined js script function mediate {org.apache.synapse.mediators.bsf.ScriptMediator}
com.sun.phobos.script.util.ExtendedScriptException: org.mozilla.javascript.EcmaError: TypeError: Cannot read property "CommoditiesList" from null (<Unknown Source>#45) in <Unknown Source> at line number 45
at com.sun.phobos.script.javascript.RhinoCompiledScript.eval(RhinoCompiledScript.java:68)
at javax.script.CompiledScript.eval(CompiledScript.java:92)
at org.apache.synapse.mediators.bsf.ScriptMediator.mediateForInlineScript(ScriptMediator.java:345)
at org.apache.synapse.mediators.bsf.ScriptMediator.invokeScript(ScriptMediator.java:265)
at org.apache.synapse.mediators.bsf.ScriptMediator.mediate(ScriptMediator.java:233)
at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:97)
at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:260)
at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.mediateFromContinuationStateStack(Axis2SynapseEnvironment.java:775)
at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:282)
at org.apache.synapse.core.axis2.SynapseCallbackReceiver.handleMessage(SynapseCallbackReceiver.java:554)
at org.apache.synapse.core.axis2.SynapseCallbackReceiver.receive(SynapseCallbackReceiver.java:188)
at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
at org.apache.synapse.transport.passthru.ClientWorker.run(ClientWorker.java:262)
at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.mozilla.javascript.EcmaError: TypeError: Cannot read property "CommoditiesList" from null (<Unknown Source>#45)
My doubt are:
what are the best way to handle situation like this?
I know that I can handle the situation inside th script mediator (and it is pretty easy: I check if the CropCalendarCommodities.CommoditiesList is null. If it is null I create a propper JSON response that will be returned to th user (something containing a 404 status message).
But my doubt is: can I centralize the management of all the possile error case in the ... sequence.
If yes in this case I need a way to retrieve the type of error occured into my .
In this case if the error is into the script mediator I can build a 404 status message that will be returned to the user. But if occurred another tyoe of error (for example DSS can't access to the DB) I will build a different error message that will be returned to the user.
What I am trying to do is to centralize the error management and handle the error situation in a manner more similar to the classical concept of exception.
Can I do this in some way?
Yes fault sequence is the place to handle errors. You can use,
You can create a custom error payload with an appropriate HTTP_SC and respond to the client.