Error Handling Camel
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transactional is the most common type that is enabled out-of-the-box and handled by Camel itself. The transaction type is handled by a backing system such as a J2EE application server.Using try ... catch defaulterrorhandler camel ... finallyRelated to error handling is the Try Catch Finally feature in Camel.When does
Camel Throw Exception
an error happenAn error happens whenany uncaught exception is thrown during routing and processing of messages within CamelSo think of onexception camel this as a big exception interceptor that catches all exceptions and handles what to do.Non transactionalBy default Camel uses the non transaction type and orchestrates the error handling during processing and routing.As there isn't
Apache Camel Log Exception
a single error handling configuration that suites all uses cases, you should consider altering the default configurations to better suit you needs.Camel 1.x default error handlerIn Camel 1.x a global Dead Letter Channel is setup as the Error Handler by default. It's configured as:redeliver up to 6 timespause 1 second between each redelivery attemptif all redelivery attempts failed then move exchange into the dead letter queuethe default camel error handling best practices dead letter queue is a logger that logs the exchange at ERROR level Dead Letter Queue (*)A dead letter queue is like a black hole, it will consume the Exchange and the Exchange routing is ended with no indication that it failed. This works great in the JMS Messaging world where we don't want a bad message to cause endless retries and causing the system to exhaust. The message is said to be poison and thus we want to move it to a dead letter queue so the system can continue to operate and work with the next message.This default does not go well with other transports using in a request/reply messaging style. If the Exchange failed then the original caller want to be alter it failed.So the bottom line is that you must configure and setup the error handling strategies that suits your business needs.Camel 2.0 onwards default error handlerIn Camel 2.0 onwards a global DefaultErrorHandler is set up as the Error Handler by default. It's configured as:no redeliveriesno dead letter queueif the exchange failed an exception is thrown and propagated back to the original caller wrapped in a RuntimeCamelException.ScopesCamel supports 2 scopes that is determined by the DSL i
alternative is to specify the error handling directly in the DSL using the Exception Clause. For introduction and background material see Error handling in Camel. Camel 2.0 has a new default error handlerIn Camel 2.0
Exception Handling In Camel Route
onwards there default error handler is changed from Dead Letter Channel to DefaultErrorHandler.
Camel Error Handler
This error handler does not support a dead letter queue and will return exceptions back to the caller. This is camel default error handler what you expects when working with regular Java that exceptions will be thrown back to the caller. Exception ClauseUsing Error Handler combined with Exception Clause is a very powerful combination. We encourage http://camel.apache.org/error-handling-in-camel.html end-users to use this combination in your error handling strategies. See samples and Exception Clause. Using try ... catch ... finallyRelated to error handling is the Try Catch Finally as DSL you can use directly in your route. Its basically a mimic of the regular try catch finally in the Java language but with more power. The current implementations Camel provides out of the box http://people.apache.org/~dkulp/camel/error-handler.html are: Non transacted DefaultErrorHandler is the default error handler in Camel 2.0 onwards. This error handler does not support a dead letter queue, it will propagate exceptions back to the caller, as if there where no error handler at all. It has a limited set of features.Dead Letter Channel which supports attempting to redeliver the message exchange a number of times before sending it to a dead letter endpointLoggingErrorHandler for just catching and logging exceptionsNoErrorHandler for no error handling Transacted TransactionErrorHandler is the default error handler in Camel 2.0 onwards for transacted routes. See the Transactional Client EIP pattern. These error handlers can be applied in the DSL to an entire set of rules or a specific routing rule as we show in the next examples. Error handling rules are inherited on each routing rule within a single RouteBuilder Transaction in Camel 1.xIf the route is transactional then the Dead Letter Channel is disabled. The exchange.isTransacted() is used to determine if an Exchange is transacted or not. So if you are using transacted routes then you should configure the TransactionErrorHandler instread of DeadLetterChannel. See Transactional Client for further details and samples. Short Summary of
technologies Tuesday, August 17, 2010 Camel exception handling overview Here are some notes on adding Camel (v2.3) http://www.consulting-notes.com/2010/08/camel-exception-handling-overview.html exception handling to a JavaDSL route. There are various approaches/options http://stackoverflow.com/questions/23491928/apache-camel-custom-error-handler-to-control-behavior-per-exception available. These notes cover the important distinctions between approaches... default handling The default mode uses the DefaultErrorHandler strategy which simply propagates any exception back to the caller and ends the route immediately. This is rarely the desired behavior, at error handling the very least, you should define a generic/global exception handler to log the errors and put them on a queue for further analysis (during development, testing, etc). onException(Exception) .to("log:GeneralError?level=ERROR") .to("activemq:GeneralErrorQueue"); try-catch-finally This approach mimics the Java for exception handling and is designed to be very readable error handling camel and easy to implement. It inlines the try/catch/finally blocks directly in the route and is useful for route specific error handling. from("direct:start") .doTry() .process(new MyProcessor()) .doCatch(Exception.class) .to("mock:error"); .doFinally() .to("mock:end"); onException This approach defines the exception clause separately from the route. This makes the route and exception handling code more readable and reusable. Also, the exception handling will apply to any routes defined in its CamelContext. from("direct:start") .process(new MyProcessor()) .to("mock:end"); onException(Exception.class) .to("mock:error"); handled/continued These APIs provide valuable control over the flow. Adding handled(true) tells Camel to not propagate the error back to the caller (should almost always be used). The continued(true) tells Camel to resume the route where it left off (rarely used, but powerful). These can both be used to control the flow of the route in interesting
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