Weld SE and synthetic container lifecycle event observers

2016-2-8   api , draft   Martin Kouba

Last week Weld 3.0.0.Alpha15 was released and so it’s time to reveal the features that should go into the next experimental release. The main goal of Weld 3.0.0.Alpha16 is to reflect the output of CDI-558. However, we would also like to continue to deliver experimental prototypes so that users could test a new functionality (that we find interesting and useful) and the CDI EG could eventually include this into CDI 2.0.

It should be easier to start playing with extensions in Weld SE. Right now, it’s possible to pass an Extension instance to the Weld builder so that it’s not necessary to configure service providers (i.e. META-INF/services/javax.enterprise.inject.spi.Extension file). In such case, the extension class is automatically scanned for observer methods and the instance is used as the receiver of the notifications. We would like to make this even easier. It is now possible to add a synthetic container lifecycle event observer without declaring an extension class. The observer logic is represented as a lambda expression. This might be especially useful for prototyping and/or for discovering how extensions work.

The starting point is the org.jboss.weld.environment.se.ContainerLifecycleObserver class. There are few static methods, each corresponding to a specific container lifecycle event (e.g. beforeBeanDiscovery()). Some variants return a builder so that it’s possible to customize the observer (observed type, priority, etc.). Others accept a lambda and return an observer instance direcly.

A synthetic observer may be added to the builder directly - see Weld.addContainerLifecycleObserver() - or grouped in a synthetic extension - see ContainerLifecycleObserver.extensionBuilder().

Extension testExtension = ContainerLifecycleObserver.extensionBuilder()
    .add(afterBeanDiscovery((e) -> System.out.println("Bean discovery completed!")))
    .add(processAnnotatedType().notify((e) -> {
            if (e.getAnnotatedType().getJavaClass().getName().startsWith("com.foo")) {

try (WeldContainer container = new Weld().addExtension(testExtension).initialize()) {
    // Use the container...

This feature is merged in the master branch. If you want to try it out, you’ll have to use a 3.0.0-SNAPSHOT version or build the Weld from source: mvn clean install. Do you find it useful? Any feedback is appreciated! Feel free to add comments to this blog post or to the corresponding issue: WELD-2012.