Apache Camel 3.x Upgrade Guide

The Consumer API in camel-api has been enhanced to help support Camel reducing the footprint during routing. One aspect is that we allow recycling Exchange instances created by the consumers. This avoids creating new Exchange instances in the memory for each incoming message consumers process. By recycling Exchange`s we reduce the overhead on the JVM garbage collector. This requires Camel to know if the `Exchange should be recycled or not, and some API changes took place.

The Consumer API has two new methods which a consumer must use to create an Exchange with createExchange. Default the exchange is auto released when its complete in use, but some consumers needs custom control, and can turn off auto release, which then requires the consumer to manually release the exchange by calling releaseExchange when the consumer is done with the exchange.

The default implementations in DefaultConsumer has adapted this API and 3rd party components can continue as is, by using the older APIs. For these 3rd party components to support recycling exchanges, then they must be updated to use this new API.

A new org.apache.camel.spi.ResourceLoader has been introduced as part of CAMEL-16285 which provide a way to support additional schemas to resolve resources. As a consequece:

As example, assuming you want to provide a support for the schema foo, then you either have to binbd your instance to the Camel Registry with resource-loader-foo as a key, or create a factory finder file with path META-INF/services/org/apache/camel/resource-resolver/foo The method for retrieving a resource URL provided by the org.apache.camel.support.ResourceHelper class, i.e. resolveMandatoryResourceAsUrl ad ` resolveResourceAsUr` have been amended to accept a CamelContext instance instead of a ClassResolver.

The properties on Exchange have been optimized to separate into two: internal state vs user properties.

The method getProperties() now only returns user properties. To include internal properties as well, then use getAllProperties().

The other APIs such as getProperty(String) works the same way as before, being able to lookup a property regardless if it is internal or custom.

The internal properties is a fixed set of known keys defined in the ExchangePropertyKey enum class. These keys are used in camel-core such as the routing engine, EIPs and others that needs to store internal state on the Exchange which is done as exchange properties. Because Camel end users can also store exchange properties then before they would get mixed together. What we have done now is to separate them.

The choice and filter EIPs no longer store exchange property Exchange.FILTER_MATCHED. The reason is the information is seldom in use, and by removing we were able to optimize camel-core.

Camel now validates that a route has only 1 onCompletion. Previously users could have code such as:

Which would lead to the last onCompletion override the first, meaning that only onCompletion().onFailureOnly() would be active. Now this is checked on startup and Camel reports an error.

The camel-spring component has been modularized into:

Also for Camel on Spring Boot:

The motivation is to move out the XML DSL from camel-spring which reduces the number of dependencies and makes the module lighter.

Users that use the Spring XML DSL (eg the top XML tag is Spring <beans>) should migrate from using camel-spring to camel-spring-xml as dependency.

Users that do not use Spring XML should not be affected.

In Spring XML <proxy> and <remote>` have been removed. They were only available in Spring XML and not in the other XML DSLs (Blueprint and CDI).

Based on the modularization of camel-spring we have made two starters available when using Camel on Spring Boot

We also made all the component -starter JARs not depend on any of the above starters, which means you must pick the one to use above, and then add which -starter JARs you want to use in your Camel spring boot applications.

The option deleteIfFiltered has been changed to use a different exchange property with key Sqs2Constants.SQS_DELETE_FILTERED which must be set. Beforehand a property by Filter EIP was being used, however this property has been removed due to optimizing core Camel.

The freemarker component now has turned off localized lookup for templates. This can be turned back on by setting localizedLookup=true on the component.

Camel-jmh, camel-performance and camel-itest-performance have been moved to a new repository https://github.com/apache/camel-performance-tests

The camel-debezium-parent module has been renamed to camel-debezium-common-parent, while the old the name is now used as parent name for the middle folder. This is an internal change that shouldn’t affect end users, added here for tracking purpose anyway.

The camel-jclouds feature for Camel on Karaf has been removed.

The camel-kafka consumer has been improved to be more roboust and have more confirations how to deal with exceptions while polling from Kafka Brokers. In case of any exception thrown, then previously the consumer will re-connect and therefore try again. This leads to Kafka broker would reasign the partions, but it may assign back the same consumer again, or another standby consumer.

The new behavior is to only retry certain kind of exceptions which Kafka has marked as retryable. Any other exceptions is now causing Camel error handler to handle the caused exception (will log by default but you can use onException etc), and then skip to next offset so the next message can be polled and processed by Camel.

See the updated camel-kafka documentation for more details.