How can i handle Apache Camel NoRouteToHostException exception? - web-services

Question

i want to treat the case when connection with Camel HTTP component cannot be established
example:
<from uri="timer:tm?period=2000"/>
<to uri="https://URI"/>
when there is no connection i get this exception:
java.net.NoRouteToHostException: No route to host: connect
I want to handle this response and change it to an understandable message by the consumer. How can i do this ?

Answer 1

Camel provides a couple of very powerful error handling mechanisms with very useful redelivery and deadletter functionality. Those include:
Error Handlers: https://camel.apache.org/error-handler.html
Dead Letter Channels: https://camel.apache.org/dead-letter-channel.html
Try, Catch & Finally: https://camel.apache.org/try-catch-finally.html
Exception Clause: https://camel.apache.org/exception-clause.html
For your usecase, Exception Clause is the best fit. Redelivery would help you to retry the HTTP call and avoid failure due to a temporary downtime, e.g. a server restart:
<onException>
<exception>java.net.NoRouteToHostException</exception>
<!-- retry 3 times with a delay of 10 seconds -->
<redeliveryPolicy maximumRedeliveries="3" logStackTrace="true" redeliveryDelay="10000" />
<!-- only logs once redeliveries have failed -->
<to uri="log:classToLog?level=ERROR"/>
</onException>

Answer 2

You can handle exception using try..catch..finally.
http://camel.apache.org/try-catch-finally.html
Example in Spring DSL:
<route id="send_request">
<from uri="timer:tm?period=2000" />
<doTry>
<to uri="https://URI" />
<doCatch>
<exception>java.net.NoRouteToHostException</exception>
<handled>
<constant>true</constant>
</handled>
<log message="Some Message : ${exception.message}"
loggingLevel="WARN" />
</doCatch>
</doTry>