Choice Exception strategy in Mule







Choice Exception strategy in Mule


You can define a choice exception strategy to customize the way Mule handles a message with an error based on the message’s content at the moment it throws an exception. A choice exception strategy catches all exceptions thrown within its parent flow, examines message contents and exception type, then routes messages to the appropriate exception strategy for processing.

Here’s how it works: when the choice exception strategy catches an exception, it evaluates the type of exception and the message contents at the time the error occurred. Then it checks the expression attribute of each of its exception strategies one by one, serially, to see which one of them should handle the error. It then routes the message to the first exception strategy that evaluates to true (has an expression that matches the expression of the message). If none of its exception strategies can handle the error, the choice exception strategy routes the message to Mule’s default exception strategy.

This exception strategy is useful when you want to handle the exception based on the message content after an exception is thrown. It catches all exceptions thrown within its parent flow, checks the message content and exception type, and then routes the message to the appropriate exception strategy. 

There is more than one exception strategy which is defined within this strategy. Catch or Rollback uses MEL to advise the Choice exception strategy as to which message it accepts and will be doing further processing. If none of the Choice exception strategies are able to handle the error, it routes the message to the default exception strategy.

A Choice exception strategy contains one or more catch or rollback exception strategies.

A Choice exception strategy cannot be nested within other choice exception strategies.

Any Mule expression evaluator can be used as the expression attribute of an exception strategy.

flow of choice exception strategy :




Settings of first block Catch Exception Strategy :



URL : http://localhost:8085/api/choiceexc
Method : POST

Input :


Since input json format is wrong so exception will occur and handled by choice exception strategy.




Output :





XML project code :


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

<mule xmlns:dw="http://www.mulesoft.org/schema/mule/ee/dw" xmlns:metadata="http://www.mulesoft.org/schema/mule/metadata" xmlns:json="http://www.mulesoft.org/schema/mule/json" xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/json http://www.mulesoft.org/schema/mule/json/current/mule-json.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/ee/dw http://www.mulesoft.org/schema/mule/ee/dw/current/dw.xsd">
    <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8085" basePath="/api" doc:name="HTTP Listener Configuration"/>
    <flow name="test_choiceexceptionFlow">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/choiceexc" doc:name="HTTP"/>
        <json:json-to-xml-transformer doc:name="JSON to XML"/>
        <dw:transform-message doc:name="Transform Message">
            <dw:set-payload><![CDATA[%dw 1.0
%output application/json
---
{
id : payload.id
}]]></dw:set-payload>
        </dw:transform-message>
        <set-payload value="#[payload]" doc:name="Set Payload"/>
        <choice-exception-strategy doc:name="Choice Exception Strategy">
            <catch-exception-strategy when="#[exception.causeMatches('java.io.IOException')]" doc:name="Catch Exception Strategy">
                <set-property propertyName="http.status" value="400" doc:name="Property"/>
                <set-payload value="Input is not correct" doc:name="Set Payload"/>
            </catch-exception-strategy>
            <catch-exception-strategy doc:name="Catch Exception Strategy">
                <set-property propertyName="http.status" value="500" doc:name="Property"/>
                <set-payload value="internal server error" doc:name="Set Payload"/>
            </catch-exception-strategy>
        </choice-exception-strategy>
    </flow>
</mule>