Understanding Apache Camel Exception Handling using Example

In this post we will implement Exception Handling for Apache Camel. In previous Apache Camel + Spring we had written a integrated Camel Java DSL and Spring.
We can write the exception handling code either in the spring configuration file or the Java DSL class. We will implement exception handling using Java DSL in this post.

Apache Camel - Table of Contents
File Transfer Using Java DSL Apache Camel
Apache Camel Java DSL + Spring Integration Hello World Example
Apache Camel Exception Handling Using Simple Example
Apache Camel Redelivery policy using example
Integrate Apache Camel and ActiveMQ
EIP patterns using Apache Camel
Apache Camel Tutorial- Integrate Spring Boot+ Apache Camel
Apache Camel Tutorial- Integrate with MySQL DB using SQL query
Apache Camel EIP - Splitter and Aggregator pattern
Apache Camel Unit Testing 
Apache Camel + Spring + Quartz Hello World Example 
Camel application deployment on JBoss Fuse 
Apache Camel + Apache CXF SOAP Webservices
Apache Camel + JAX-RS REST Webservice
Apache Camel + CXFRS REST Webservice
Apache Camel Routing Slip EIP Pattern
Apache Camel Dynamic Router Pattern
Apache Camel Load Balancer EIP Pattern
Apache Camel Interceptors
Apache Camel + Kafka Hello World Example
Apache Camel - Marshalling/Unmarshalling XML/JSON Data Example
Calling and Consuming Webservices using Apache Camel
Apache Camel Tutorial - Send SMTP Email Using Gmail
Apache Camel Tutorial - SEDA component Hello World Example
Spring Boot + Apache Camel + RabbitMQ - Hello World Example
Apache Camel Tutorial - Idempotent Consumer using MemoryIdempotentRepository and FileIdempotentRepository
Spring Boot + Apache Camel JDBC component + MySQL - Hello World Example 
Spring Boot + Apache Camel SQL component + MySQL - Hello World Example
Spring Boot + Apache Camel SQL component + Transaction Management Example

Lets Begin

The project in the previous Apache Camel + Spring would be the starting point for this tutorial.
The project structure will be as follows-


The exception handling for Apache camel can be implemented in 2 ways.

• Using Do Try block
• Using OnException block

Define a custom exception as follows-

package com.javainuse.exception;
public class CamelCustomException extends Exception {
    private static final long serialVersionUID = 1L;
}

Next we throw this custom exception once from the MyProcessor.java which will be called from our Java DSL route.

package com.javainuse.processor;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import com.javainuse.exception.CamelCustomException;

public class MyProcessor implements Processor {

    public void process(Exchange exchange) throws Exception {
        System.out.println("Exception Thrown");
        throw new CamelCustomException();
    }

}

Currently our SimpleRouteBuilder code is as follows. There is no exception handling code written. So the message will keep retrying as the exception is not handled.

package com.javainuse.route;

import org.apache.camel.builder.RouteBuilder;
import com.javainuse.processor.MyProcessor;

public class SimpleRouteBuilder extends RouteBuilder {

    @Override
    public void configure() throws Exception {
        from("file:C:/inputFolder?noop=true").process(new MyProcessor()).to("file:C:/outputFolder");
    }

}

Now lets have a look at the exception handling code

• Using Do Try block
  This approach is similar to the Java try catch block. So the thrown exception will be immediately caught and the message wont keep on retrying.
  

  package com.javainuse.route;
  
  import org.apache.camel.builder.RouteBuilder;
  import com.javainuse.processor.MyProcessor;
  
  public class SimpleRouteBuilder extends RouteBuilder {
  
      @Override
      public void configure() throws Exception {
           from("file:C:/inputFolder?noop=true").doTry().process(new MyProcessor()).to("file:C:/outputFolder")
              .doCatch(CamelCustomException.class).process(new Processor() {
  
                  public void process(Exchange exchange) throws Exception {
                      System.out.println("handling ex");
                  }
              }).log("Received body ");
  
  }
  

  
  
  
  
  The limitation of this approach is that it is applicable only for the single route.
  Suppose we have one more seperate route. Then if an exception occurs in that route then it will not be handled by the current doTry block.

  package com.javainuse.route;
  
  import org.apache.camel.Exchange;
  import org.apache.camel.Processor;
  import org.apache.camel.builder.RouteBuilder;
  import com.javainuse.exception.CamelCustomException;
  import com.javainuse.processor.MyProcessor;
  
  public class SimpleRouteBuilder extends RouteBuilder {
  
      @Override
      public void configure() throws Exception {
          from("file:C:/inputFolder?noop=true").doTry().process(new MyProcessor()).to("file:C:/outputFolder")
              .doCatch(CamelCustomException.class).process(new Processor() {
  
                  public void process(Exchange exchange) throws Exception {
                      System.out.println("handling ex");
                  }
              }).log("Received body ");
  
          from("file:C:/inbox?noop=true").process(new MyProcessor()).to("file:C:/outbox");
      }
  
  }
  

  
  
  
  So the exception thrown in the route from from("file:C:/inbox?noop=true") will not be handled.
• Using OnException block
  The OnException block is written as a separate block from the routes.
  This applies to all the routes. Below for both route starting with from("file:C:/inputFolder?noop=true") and from("file:C:/inbox?noop=true") the exception handling will be applied.
  

  package com.javainuse.route;
  
  import org.apache.camel.Exchange;
  import org.apache.camel.Processor;
  import org.apache.camel.builder.RouteBuilder;
  import com.javainuse.exception.CamelCustomException;
  import com.javainuse.processor.MyProcessor;
  
  public class SimpleRouteBuilder extends RouteBuilder {
  
      @Override
      public void configure() throws Exception {
  
          onException(CamelCustomException.class).process(new Processor() {
  
              public void process(Exchange exchange) throws Exception {
                  System.out.println("handling ex");
              }
          }).log("Received body ").handled(true);
  
          from("file:C:/inputFolder?noop=true").process(new MyProcessor()).to("file:C:/outputFolder");
  
          from("file:C:/inbox?noop=true").process(new MyProcessor()).to("file:C:/outputFolder");
      }
  
  }
  

We get the output as follows

So Exception thrown from both routes are handled by the onException Block.

Download Source Code

Download it - Apache Camel Exception Handling Example

See Also
Spring Boot Hello World Application- Create simple controller and jsp view using Maven
Spring Boot Tutorial-Spring Data JPA
Spring Boot + Simple Security Configuration
Pagination using Spring Boot Simple Example
Spring Boot + ActiveMQ Hello world Example
Spring Boot + Swagger Example Hello World Example
Spring Boot + Swagger- Understanding the various Swagger Annotations
Spring Boot Main Menu
Spring Boot Interview Questions