In Apache Camel, in almost all use cases, we will be using onException(SomeException.class).handled(true).
Is there any use cases where we need to use onException(SomeException.class).handled(false)?
If we use onException(false), the Exception will be returned to the caller, even though you can change the body in the handling code (original route propagation will be stopped). But if you use handled(false), then can we retrieve the Exchange object to get the original message at the caller? You will only get the Exception, right?
Please check http://camel.465427.n5.nabble.com/What-s-the-Difference-between-handled-false-and-continued-true-and-more-td4302302.html
As you can see there are the following rules provided by Claus Ibsen:
handle(true) = the exception is handled and removed from the exchange + break out routing
handled(false) = the exception is not handled, so it will be stored as an exception on the exchange + break out routing
continue(true) = handled(true) + continue routing
Related
I would like to know if the below is expected behaviour for Camel idempotent consumer:
I have removeOnFailure=true for the route, which means basically when the exchange fails idempotent consumer should remove the Identifier from the repository. This brings up a very interesting scenario which allows duplicate on the exchange.
Suppose I have identifier=12345 and first attempt to execute the exchange was Succesfull which means identifier is added to idempotent repository. Next attempt to use same identifier i.e 12345 fails as this is caught as Duplicate Message (CamelDuplicateMessage). But at this point having removeOnFailure=true will remove the identifier from the repository which on next attempt will allow the exchange to go through successfully without catching the default message. Hence, creating a room for duplication on the exchange.
Can someone advise if this is expected behaviour or some bug?
Sample Route:
from("direct:Route-DeDupeCheck").routeId("Route-DeDupeCheck")
.log(LoggingLevel.DEBUG, "~~~~~~~ Reached to Route-DeDupeCheck: ${property.xref}")
.idempotentConsumer(simple("${property.xref}"), MemoryIdempotentRepository.memoryIdempotentRepository()) //TODO: To replace with Redis DB for caching
.removeOnFailure(true)
.skipDuplicate(false)
.filter(exchangeProperty(Exchange.DUPLICATE_MESSAGE).isEqualTo(true))
.log("~~~~~~~ Duplicate Message Found!")
.to("amq:queue:{{jms.duplicateQueue}}?exchangePattern=InOnly") //TODO: To send this to Duplicate JMS Queue
.throwException(new AZBizException("409", "Duplicate Message!"));
Your basic premise is wrong.
Next attempt to use same identifier i.e 12345 fails as this is caught
as Duplicate Message (CamelDuplicateMessage)
When there is a duplicated message, it is not considered as a failure. It is just ignored from further processing(unless you have skipDuplicate option set to true).
Hence the scenario what you just explained cannot occur what so ever.
It is very easy to test. Considering you have a route like this,
public void configure() throws Exception {
//getContext().setTracing(true); Use this to enable tracing
from("direct:abc")
.idempotentConsumer(header("myid"),
MemoryIdempotentRepository.memoryIdempotentRepository(200))
.removeOnFailure(true)
.log("Recieved id : ${header.myid}");
}
}
And a Producer like this
#EndpointInject(uri = "direct:abc")
ProducerTemplate producerTemplate;
for(int i=0, i<5,i++) {
producerTemplate.sendBodyAndHeader("somebody","myid", "1");
}
What you see in logs is
INFO 18768 --- [tp1402599109-31] route1 : Recieved id : 1
And just once.
I'm trying to send a message from an Activiti Camel task to an ActiveMQ queue, which should resume the activity when it is received by Camel. As I understand it, when the message is received from the queue lacks the properties that would enable it to be identified by Camel in order to be routed to the correct activity task.
As such a Business key is Null Exception is raised and the route fails.
from("activiti:SampleProcess:myCamelTask")
.to("activemq:queue:myQueue");
As expected, if I hardcode either the PROCESS_ID_PROPERTY or the PROCESS_KEY_PROPERTY in the receiving route, the message is routed correctly (when the ID matches).
from("activemq:queue:myQueue")
.setBody(constant("test body"))
.setProperty(PROCESS_ID_PROPERTY, constant("50"))
// .setProperty(PROCESS_KEY_PROPERTY, constant("CUSTOM-KEY"))
.to("activiti:SampleProcess:receiveAsyncPing");
How can I get either property in the receiving route so I can set them accordingly?
Or is there a more recommended way to approach this?
A good question.
The way I handled this is to inject the PROCESS_KEY within the route using the setProperty() command:
See below where I set the process key (business key) to "bar":
from(startProcessEndpoint)
.log(LoggingLevel.INFO, logMsg3)
.setProperty("PROCESS_KEY_PROPERTY",foo)
.setBody(constant("bar"))
.to("activiti:testCamelTask:receive")
Now, if you dont want to use a constant, then you have access to the exchange object within the route and can use an Expression as shown below:
Expression foo = new Expression() {
#Override
public <T> T evaluate(Exchange exchange, Class<T> aClass) {
return (T) "foo";
}
};
Hope this helps,
Greg
I’m working on Camel and focusing on Error Handling.
For irrecoverable errors (those that won’t be fixed by retries), Camel In Action says you should use exchange.getOut().setFault(true) and exchange.getOut().setBody("Error Occurred").
What is the best way to actually handle these errors? Right now I’m thinking there’s two ways:
Using handleFaults(true) on the route or context then handling like any other errors
The original message sender could handle it if Request Reply pattern is used
1 is straight forward to me (except at that point, might as well use Exceptions/Recoverable errors?). 2 is a little trickier – I’m not sure how the original sender will know that the message that they get back is an error (vs. the expected return message).
What I’m thinking could happen is this using Exception to indicate that it’s an error:
In route:
// error occurred
exchange.getOut().setFault(true);
exchange.getOut().setBody(new Exception(“error”));
In sender (jms example using QueueRequestor for Request Reply):
responseMessage = qRequestor.request(msg);
if(responseMessage instanceof ObjectMessage && ((ObjectMessage)responseMessage).getObject() instanceof Exception) {
// AN ERROR OCCURRED IN ROUTE
} else {
// NORMAL PROCESSING OF MESSAGE
}
This just seems like a lot of work on the original sender. Is there a better way of handling this?
Camel can handle the exception well out of box with the help of ErrorHandler, which means your camel route don't need to do much thing about it.
But for the fault message, it's a part of Application level message, Camel ErrorHandler don't want to touch it, so the developer should think about how to handle it.
I would like to process both request and response messages at the end of my route. However, I do not see a way how to access the original request message.
I have the terrible feeling I am struggling with some basic concept.
Here is a simple example route in DSL to outline my problem (streamCaching is enabled for the whole context):
from("activemq:queue:myQueue")
.to("log:" + getClass().getName() + "?showOut=true")
.to("http://localhost:8080/someBackend")
.log("Now in.Body returns this: ${in.body} and out.Body this: ${out.body}")
.to("log:" + getClass().getName() + "?showOut=true");
Here is an according excerpt from my logs (line-breaks edited for better reading). As one can see, the original SOAP message is lost once the http server replied, and the SOAP response object is stored in the inBody of the message.
2012-09-25 17:28:08,312 local.bar.foo.MyRouteBuilder INFO -
Exchange[ExchangePattern:InOut, BodyType:byte[],
Body:<?xml version="1.0" encoding="UTF-8"?><env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"><env:Header /><env:Body><urn:someRequest xmlns:urn="http://foo.bar.local/ns"></urn:someRequest></env:Body></env:Envelope>,
Out: null]
2012-09-25 17:28:08,398 org.apache.camel.component.http.HttpProducer DEBUG -
Executing http POST method: http://localhost:8080/someBackend
2012-09-25 17:28:09,389 org.apache.camel.component.http.HttpProducer DEBUG -
Http responseCode: 200
2012-09-25 17:28:09,392 route2 INFO -
Now in.Body returns this: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"><soap:Body><ns2:someResponse xmlns:ns2="http://foo.bar.local/ns"</ns2:someResponse></soap:Body></soap:Envelope>
and out.Body this:
2012-09-25 17:28:09,392 local.bar.foo.MyRouteBuilder INFO -
Exchange[ExchangePattern:InOut,
BodyType:org.apache.camel.converter.stream.InputStreamCache,
Body:[Body is instance of org.apache.camel.StreamCache],
Out: null]
I would have expected to have in.body and out.body be preserved across the whole route?
Alternative solutions I am considering:
Make use of the Correlation Identifier pattern to correlate both request and reply. But would this preserve the message bodies as well? Also, my request/reply messages do not have unique identifiers for correlation.
Write a custom bean, which performs the call to the http backend, processing both request and reply objects (but this is basically a no-Camel solution, reinventing the wheel and hence not preferred)
Already failed approaches:
I tried to access the original request message using a Processor like this at the end of my route, with no success:
process(new Processor() {
#Override
public void process(Exchange exchange) throws Exception {
Message originalInMessage = exchange.getUnitOfWork().getOriginalInMessage();
logger.debug(originalInMessage.getBody(String.class));
logger.debug(exchange.getIn().getBody(String.class));
}
});
Thanks for any help
Simply store the original body of the in message in a header or a property and retrieve it at the end:
from("activemq:queue:myQueue")
.setProperty("origInBody", body())
.to("http://localhost:8080/someBackend")
After the http call you can then access the property origInBody.
First, this article shows very well how in and out works in camel: http://camel.apache.org/using-getin-or-getout-methods-on-exchange.html
Typically, the out message is not always used, but rather copied from the in-message in each step.
In your case, where you want the original message to stay around til the end of the route, you could go ahead with the Enrichment EIP. http://camel.apache.org/content-enricher.html
Your route would be something like this:
public class MyAggregationStrategy implements AggregationStrategy {
public Exchange aggregate(Exchange orig, Exchange httpExchange){
// if you want to check something with the Http request, you better do that here
if( httpExchange is not correct in some way )
throw new RuntimeException("Something went wrong");
return orig;
}
}
AggregationStrategy aggStrategy = new MyAggregationStrategy();
from("activemq:queue:myQueue")
.enrich("http://localhost:8080/someBackend",aggStrategy)
.//keep processing the original request here if you like, in the "in" message
One of the biggest problem of camel, is the ease to misuse it. The best way to use it correctly is to think in terms of EIP : one of the main goals of camel, is to implement EIP in its DSL.
Here is a list of EIP
Now think about it. You want the request and the response at the end, for what use ? Logging, Aggregation, ... ? For logging, a correlationId should suffice, so I presume you need it to create a response, based on both request and the proxied-response. If that's what you want, you could do something like
from("direct:receiveRequest")
.enrich("direct:proxyResponse", new RequestAndResponseAggregationStrategy())
You will have the opportunity to merge your Request (in oldExchange) and your Response (in newExchange).
With all the due respect I have for Christian Schneider, I do think the idea of putting the request in a property that could be reused later is a bad design. By doing it, you create side-effect between your routes. If your route is a subroute for another, you'll maybe erase their property. If you store it to put it back later, maybe you should do something like
from("direct:receiveRequest")
.enrich("direct:subRouteToIgnoreResponse", AggregationStrategies.useOriginal())
A really really bad design that I have done too many time myself is to do :
from("direct:receiveRequest")
.to("direct:subroute")
from("direct:subroute")
.setProperty("originalBody", body())
.to("direct:handling")
.transform(property("originalBody")
This will lead to "properties/headers hell", and to routes that are just a successive call of processors.
And if you can't think of a solution of your problem with EIP, you should maybe use camel only to access their components. For example, something like :
from("http://api.com/services")
.to(new SomeNotTranslatableToEIPProcessor())
.to("ftp://destination")
But don't forget that those components has their own goals : creating a common abstraction between similar behaviour (e.g, time based polling consumer). If you have a very specific need, trying to bend a camel component to this specific need can lead to huge chunk of code not easily maintainable.
Don't let Camel become your Golden Hammer anti-pattern
I often use an aggregation strategy, which preserves the old exchange and puts the result of the enrich into a header:
import org.apache.camel.Exchange;
import org.apache.camel.processor.aggregate.AggregationStrategy;
public class SetBodyToHeaderAggregationStrategy implements AggregationStrategy {
private String headerName = "newBody";
public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
oldExchange.getIn().setHeader(headerName, newExchange.getIn().getBody());
return oldExchange;
}
#SuppressWarnings("unused")
public void setHeaderName(String headerName) {
this.headerName = headerName;
}
}
Now you can use it like this:
<enrich strategyRef="setBodyToHeaderAggregationStrategy">
<constant>dosomething</constant>
</enrich>
<log loggingLevel="INFO" message="Result body from enrich: ${header.newBody}. Original body: ${body}" loggerRef="log"/>
Sporadically, I receive an error in my WP7 Silverlight application. The error is a random "System.NotSupportedException". This error is thrown occassionally when the following code is executed:
// 1. Build the url
string serviceURL = "http://www.mydomain.com/service.svc/param1/param2";
// 2. Asynchronously execute the query using HttpWebRequest instead of WebClient. There is a UI performance issue with the WebClient currently
WebRequest request = HttpWebRequest.Create(serviceUrl);
request.BeginGetResponse(new AsyncCallback(MyService_Completed), request);
...
private void MyService_Completed(IAsyncResult result)
{
// Do stuff
}
I have verified that the URL I am sending is correct. Please note, that this request is part of my view model, which may have other network requests fired off at the same time. I have no idea why this happens ocassionally. Can anybody point out any potential reasons?
Thank you!
When this happens, make sure you look at the View Detail part of the exception report. It might be that your service is refusing connection or the data passed is invalid. NotSupported is a very general exception that covers many possible situations.
A similar question has been asked previously. If you look at the comments the original poster added to the answer, he claims to have solved the problem by replacing
request.BeginGetResponse(new AsyncCallback(MyService_Completed), request);
with
request.BeginGetResponse( MyService_Completed, request);