Apache Camel Exception Handling + Spring Boot Example(2024) | TechGeekNext


Apache Camel Exception Handling + Spring Boot Example

Apache Camel

Overview

In this article, we will understand different approaches of handling Exceptions in Apache Camel.

What is a Apache Camel?

Apache Camel is an open-source integration framework for implementing various Enterprise Integration Patterns(EIPs), that allows you to quickly and easily connect different systems that consume or produce data.

It is easy to use Domain Specific Languages (DSLs) to wire EIPs and transports together

Camel receives messages from some endpoint and sends it to another one. The messages can be processed or simply routed to different endpoint depending on transformation logic applied in Camel.

Apache Camel

It allows integration simple by providing connectivity to a wide variety of transports and APIs.
For example, you can easily route JMS to JSON, JSON to JMS, HTTP to JMS, FTP to JMS, even HTTP to HTTP, and connectivity to Microservices.

In this tutorial will take the example from the previous article Apache Camel with Spring Boot Simple Example.

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Project Structure

Apache Camel Project Structure

There are two ways to incorporate exception management in Apache Camel.

  • Do Try block
  • OnException block

To understand the exception handling in apache camel, will explicitly throw the exception as given below

Create Custom Exception Class to throw exception

package com.techgeeknext.camel.custom.exceptions;

public class GenericCamelCustomException extends RuntimeException {

    private static final long serialVersionUID = 7607128449240157466L;
    public GenericCamelCustomException(String message){
        super(message);
    }
}

Then, call above custom exception from Processor Class called ProcessorCustomException, which will get thrown from DSL Route (ActiveMQMsgConsumerRoute).
package com.techgeeknext.camel.custom.exceptions;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;

public class ProcessorCustomException implements Processor{

    public void process(Exchange exchange) throws Exception {
        System.out.println("Custom Exception from ProcessorCustomException.");
        throw new GenericCamelCustomException("Custom Exception from ProcessorCustomException.");
    }
}

Then, call above custom exception from Processor Class called ProcessorCustomException, which will get thrown from DSL Route (SimpleMessageRoute).

package com.techgeeknext.camel.custom.exceptions;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;

public class ProcessorCustomException implements Processor{

    public void process(Exchange exchange) throws Exception {
        System.out.println("Custom Exception from ProcessorCustomException.");
        throw new GenericCamelCustomException("Custom Exception from ProcessorCustomException.");
    }
}
Note: In this DSL SimpleMessageRoute class, we are explicitly throwing exception using ProcessorCustomException. 
package com.techgeeknext.camel.routes;

import com.techgeeknext.camel.custom.exceptions.ProcessorCustomException;
import org.apache.camel.builder.RouteBuilder;
import org.springframework.stereotype.Component;

@Component
public class SimpleMessageRoute extends RouteBuilder {

    @Override
    public void configure() throws Exception {

        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel - TechGeekNext")
                .log("")
                //throw custom exception
                .process(new ProcessorCustomException());
                //send this message to ActiveMQ queue
               // .to("activemq:my-activemq-queue");
    }
}
Output: As you can see, it's throwing the exception in the console. 
  .   ____          _ __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::     (v2.4.5)

12:53:00.237  INFO 26336 --- [main] c.t.c.CamelSprintBootServiceAApplication : Starting CamelSprintBootServiceAApplication using Java 12.0.2 on PID 26336 (D:\camel-sprint-boot-service-a\target\classes started in D:\camel-sprint-boot-service-a)
12:53:00.239  INFO 26336 --- [main] c.t.c.CamelSprintBootServiceAApplication : No active profile set, falling back to default profiles: default
12:53:01.431  INFO 26336 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
12:53:01.443  INFO 26336 --- [main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
12:53:01.443  INFO 26336 --- [main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.45]
12:53:01.627  INFO 26336 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
12:53:01.627  INFO 26336 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1356 ms
12:53:01.791  INFO 26336 --- [main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
12:53:02.237  INFO 26336 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
12:53:02.381  INFO 26336 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Routes startup summary (total:1 started:1)
12:53:02.382  INFO 26336 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Started route1 (timer://active-mq-timer)
12:53:02.382  INFO 26336 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Apache Camel 3.9.0 (camel-1) started in 153ms (build:32ms init:109ms start:12ms)
12:53:02.384  INFO 26336 --- [main] c.t.c.CamelSprintBootServiceAApplication : Started CamelSprintBootServiceAApplication in 2.462 seconds (JVM running for 2.869)
12:53:03.389  INFO 26336 --- [active-mq-timer] route1  : Hello Message from Apache Camel - TechGeekNext
Custom Exception from ProcessorCustomException.
12:53:03.417 ERROR 26336 --- [active-mq-timer] o.a.c.p.e.DefaultErrorHandler : Failed delivery for (MessageId: 8EFEE4761268FE1-0000000000000000 on ExchangeId: 8EFEE4761268FE1-0000000000000000). Exhausted after delivery attempt: 1 caught:

com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException: Custom Exception from ProcessorCustomException.
	at com.techgeeknext.camel.custom.exceptions.ProcessorCustomException.process(ProcessorCustomException.java:10) ~[classes/:na]
	at org.apache.camel.support.processor.DelegateSyncProcessor.process(DelegateSyncProcessor.java:66) ~[camel-support-3.9.0.jar:3.9.0]
	at org.apache.camel.processor.errorhandler.RedeliveryErrorHandler$SimpleTask.run(RedeliveryErrorHandler.java:439) ~[camel-core-processor-3.9.0.jar:3.9.0]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor$Worker.schedule(DefaultReactiveExecutor.java:181) ~[camel-base-engine-3.9.0.jar:3.9.0]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor.scheduleMain(DefaultReactiveExecutor.java:62) ~[camel-base-engine-3.9.0.jar:3.9.0]
	at org.apache.camel.processor.Pipeline.process(Pipeline.java:167) ~[camel-core-processor-3.9.0.jar:3.9.0]
	at org.apache.camel.impl.engine.CamelInternalProcessor.process(CamelInternalProcessor.java:388) ~[camel-base-engine-3.9.0.jar:3.9.0]
	at org.apache.camel.component.timer.TimerConsumer.sendTimerExchange(TimerConsumer.java:209) ~[camel-timer-3.9.0.jar:3.9.0]
	at org.apache.camel.component.timer.TimerConsumer$1.run(TimerConsumer.java:76) ~[camel-timer-3.9.0.jar:3.9.0]
	at java.base/java.util.TimerThread.mainLoop(Timer.java:556) ~[na:na]
	at java.base/java.util.TimerThread.run(Timer.java:506) ~[na:na]

Now, let's take a look how to handling exception using below approaches:

Do Try block approach:

This approach is identical to the try catch block in Java. As a result, the thrown exception will be caught instantly, and the message will not keep retrying.

Modified SimpleMessageRoute Route example to use 'do try' approach to handle the exception.

package com.techgeeknext.camel.routes;

import com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException;
import com.techgeeknext.camel.custom.exceptions.ProcessorCustomException;
import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;
import org.springframework.stereotype.Component;

@Component
public class SimpleMessageRoute extends RouteBuilder {

    @Override
    public void configure() throws Exception {

        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel - TechGeekNext")
                .log("")
                .doTry().process(new ProcessorCustomException())
                .doCatch(GenericCamelCustomException.class).process(new Processor() {
                    public void process(Exchange exchange) throws Exception {
                        System.out.println("Handled exception from try catch.");
                    }
                });
    }
}

Output: Run the above program, you can see the exception got handled in catch block.

  .   ____          _ __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::     (v2.4.5)

15:44:46.031  INFO 26188 --- [main] c.t.c.CamelSprintBootServiceAApplication : Starting CamelSprintBootServiceAApplication using Java 12.0.2 on PID 26188 (D:\camel-sprint-boot-service-a\target\classes started in D:\camel-sprint-boot-service-a)
15:44:46.034  INFO 26188 --- [main] c.t.c.CamelSprintBootServiceAApplication : No active profile set, falling back to default profiles: default
15:44:47.179  INFO 26188 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
15:44:47.193  INFO 26188 --- [main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
15:44:47.193  INFO 26188 --- [main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.45]
15:44:47.384  INFO 26188 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
15:44:47.384  INFO 26188 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1319 ms
15:44:47.537  INFO 26188 --- [main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
15:44:48.006  INFO 26188 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
15:44:48.194  INFO 26188 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Routes startup summary (total:1 started:1)
15:44:48.196  INFO 26188 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Started route1 (timer://active-mq-timer)
15:44:48.196  INFO 26188 --- [main] o.a.c.impl.engine.AbstractCamelContext   : Apache Camel 3.9.0 (camel-1) started in 199ms (build:36ms init:150ms start:13ms)
15:44:48.201  INFO 26188 --- [main] c.t.c.CamelSprintBootServiceAApplication : Started CamelSprintBootServiceAApplication in 2.495 seconds (JVM running for 2.993)
15:44:49.215  INFO 26188 --- [active-mq-timer] route1  : Hello Message from Apache Camel - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception from try catch.

Limitation of using do try Approach

The downside of this approach is that it is only applicable for one route.

Assume we have one more routes says route 1 and route2. If an exception exists in one of the route, the current doTry block can not handle it both route exception.

package com.techgeeknext.camel.routes;

import com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException;
import com.techgeeknext.camel.custom.exceptions.ProcessorCustomException;
import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;
import org.springframework.stereotype.Component;

@Component
public class SimpleMessageRoute extends RouteBuilder {

    @Override
    public void configure() throws Exception {

        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel - TechGeekNext")
                .log("")
                .doTry().process(new ProcessorCustomException())
                .doCatch(GenericCamelCustomException.class).process(new Processor() {
                    public void process(Exchange exchange) throws Exception {
                        System.out.println("Handled exception from try catch.");
                    }
                });

        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel - TechGeekNext")
                .log("")
                //throw custom exception
                .process(new ProcessorCustomException());
    }
}

Output: Run the program, you can notice that route1 exception got handled using do try approach, whereas route2 exception has not been handled and thrown exception.

15:57:59.048  INFO 6972 --- [main] c.t.c.CamelSprintBootServiceAApplication : Started CamelSprintBootServiceAApplication in 2.448 seconds (JVM running for 2.847)
15:58:00.059  INFO 6972 --- [active-mq-timer] route1  : Hello Message from Apache Camel Route1 - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception from try catch.

15:58:00.065  INFO 6972 --- [active-mq-timer] route2  : Hello Message from Apache Camel Route2- TechGeekNext
Custom Exception from ProcessorCustomException.
15:58:00.077 ERROR 6972 --- [active-mq-timer] o.a.c.p.e.DefaultErrorHandler : Failed delivery for (MessageId: 7A3E31DBFC5BBC3-0000000000000000 on ExchangeId: 7A3E31DBFC5BBC3-0000000000000000). Exhausted after delivery attempt: 1 caught: com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException: Custom Exception from ProcessorCustomException.
com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException: Custom Exception from ProcessorCustomException.
	at com.techgeeknext.camel.custom.exceptions.ProcessorCustomException.process(ProcessorCustomException.java:10) ~[classes/:na]
	at org.apache.camel.support.processor.DelegateSyncProcessor.process(DelegateSyncProcessor.java:66) ~[camel-support-3.9.0.jar:3.9.0]

Solution

Solution is to use OnException block approach, so that the exception handling would be applicable to all routes of that class.
OnException block approach

Modify SimpleMessageRoute class to handle exception using OnException block approach.

package com.techgeeknext.camel.routes;

import com.techgeeknext.camel.custom.exceptions.GenericCamelCustomException;
import com.techgeeknext.camel.custom.exceptions.ProcessorCustomException;
import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;
import org.springframework.stereotype.Component;

@Component
public class SimpleMessageRoute extends RouteBuilder {

    @Override
    public void configure() throws Exception {

        onException(GenericCamelCustomException.class).process(new Processor() {
            public void process(Exchange exchange) throws Exception {
                System.out.println("Handled exception using onException block.");
            }
        }).log("").handled(true);


        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel Route1 - TechGeekNext")
                .log("")
                //throw custom exception
                .process(new ProcessorCustomException());

        //generates an event/constant message every 60 seconds
        from("timer:active-mq-timer?period=60000")
                .transform().constant("Hello Message from Apache Camel Route2 - TechGeekNext")
                .log("")
                //throw custom exception
                .process(new ProcessorCustomException());
    }
}

Output: Run the above program and you can notice exception is getting handled for both Route1 and Route2.

16:09:55.002  INFO 14956 --- [main] c.t.c.CamelSprintBootServiceAApplication : Started CamelSprintBootServiceAApplication in 2.268 seconds (JVM running for 2.71)
16:09:56.007  INFO 14956 --- [active-mq-timer] route1 : Hello Message from Apache Camel Route1 - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception using onException block.
16:09:56.026  INFO 14956 --- [active-mq-timer] route1 : Hello Message from Apache Camel Route1 - TechGeekNext
16:09:56.031  INFO 14956 --- [active-mq-timer] route2 : Hello Message from Apache Camel Route2 - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception using onException block.
16:09:56.033  INFO 14956 --- [active-mq-timer] route2 : Hello Message from Apache Camel Route2 - TechGeekNext
16:10:56.006  INFO 14956 --- [active-mq-timer] route1 : Hello Message from Apache Camel Route1 - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception using onException block.
16:10:56.007  INFO 14956 --- [active-mq-timer] route1 : Hello Message from Apache Camel Route1 - TechGeekNext
16:10:56.038  INFO 14956 --- [active-mq-timer] route2 : Hello Message from Apache Camel Route2 - TechGeekNext
Custom Exception from ProcessorCustomException.
Handled exception using onException block.

Download Source Code

The full source code for this article can be found on below.
Download it here - Apache Camel Exception Handling + Spring Boot Example







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