Weld 3.0.0.Alpha12 - CDI 2.0 EDR1 Reference Implementation!

2015-8-5   release , cdi2   Martin Kouba

Weld 3.0.0.Alpha12 has been released. Compared to previous alpha releases this is an important milestone - it’s a reference implementation of CDI 2.0 Early Draft (EDR1). You can read more about CDI 2.0 EDR1 on the official blog: CDI 2.0 Early Draft Review 1 released.

Bootstrapping a CDI container in Java SE

Starting a CDI container is now really that easy:

public static void main(String... args) {
    try(CDI<Object> cdi = CDI.getCDIProvider().initialize()) {
        ComputingService service = cdi.select(ComputingService.class).get();

javax.enterprise.inject.spi.CDI now implements AutoCloseable and can therefore be used in a try-with-resources block.

Note that the specification of the bean discovery process in Java SE is not finished yet. Therefore, bean archives which don’t contain a beans.xml file are not supported. The main reason is that we don’t want to implement a feature which is being discussed and will likely undergo some important changes. Nevertheless, the feature will be implemented in one of the next alpha versions.

Weld SE bootstrap API

How does it compare to Weld SE bootstrap API? Weld has provided support for the Java SE environment for a long time. Recently, the org.jboss.weld.environment.se.Weld class was turned into a powerful builder which allows to configure the Weld container before it is initialized.

Typical usage of the Weld SE API looks like this:

try (WeldContainer container = new Weld().initialize()) {
    ComputingService service = container.select(ComputingService.class).get();

This looks very similar to CDI SE, right? However, there are several advanced feratures available:

  • automatic scanning can be disabled, classes or packages can be selected explicitly

    • WeldContainer container = new Weld().disableDiscovery().beanClasses(Foo.class, Bar.class).alternatives(Bar.class).interceptors(FooInterceptor.class).initialize();

  • WeldContainer allows to fire events easily

    • container.event().select(Bar.class).fire(new Bar());

  • Weld-specific configuration options can be specified using the builder

  • it is possible to start multiple independent Weld instances (specification does not require this)

See also Weld 3.0.0.Alpha8 announcement for more information.

Asynchronous Events

An experimental support of asynchronous events is implemented in Weld since 3.0.0.Alpha3. However, in this release the API was aligned with CDI 2.0 EDR1:

class OrderProcessor {

    @Inject Event<Order> orderEvent;

    public void process(Order order) {
        orderEvent.fireAsync(order).thenAccept((o)->System.out.println("Asynchronous processing finished: " + o.getId()));

    public void processingOrder(@Observes Order event) {
        // This observer is notified synchronously, before the fireAsync() method returns

    public void asyncProcessingOrder(@ObservesAsync Order event) {
        // This observer is notified asynchronously, in a different thread

There are few important things to notice:

  • the event was triggered with fireAsync()

  • the asynchronous observer is defined by @ObservesAsync

  • synchronous observers defined by @Observes are also notified!

To sum it up:

Event method @Observes notified @ObservesAsync notified


yes, in the same thread



yes, in the same thread

yes, in a different thread

Observers SPI Changes

javax.enterprise.inject.spi.ObserverMethod now extends javax.enterprise.inject.spi.Prioritized and overrides the ObserverMethod.getPriority() method which is used to determine the notification order in which the event observer methods are invoked. Prioritized interface is currently only used for observers. However, the Weld team is working on a prototype where Prioritized can be used to globally select/enable custom alternative beans, interceptors and decorators, see also WELD-2000.

Furthermore, ObserverMethod.isAsync() method was added to determine whether an observer method is asynchronous or not.

WildFly Patch

As usual, a patch for WildFly is available. This patch not only upgrades Weld within an existing WildFly instance but also upgrades CDI API to 2.0 EDR1. This time the target platform is WildFly 10.0.0.Alpha6. If you’re not familiar with patching WildFly, check Markus’s tutorial.