Weld Tip 2 - Development Mode

2016-10-7   tips   Martin Kouba

In this article we’re going to cover the special mode for application development. When enabled, a built-in tool called Probe provides a detailed insight into internals of a CDI application. Probe makes it easy to inspect:

  • bean archives

  • beans and their properties such as qualifiers, stereotypes and name

  • a graph of bean dependencies

  • observers and producers declared by beans

  • interceptors and decorators bound to a bean

  • extensions

  • information about current contextual instances

  • tracking of invocations and invocation trees

  • tracking of fired events

  • Weld configuration

  • and more!

Ok, now let’s get it working!

How to enable the development mode

No surprise that the development mode is DISABLED by default. It should NEVER be used in production as it may have negative impact on performance and/or represent a potential security risk. Note that if you successfully enable the development mode you should see Weld Development Mode: ENABLED warning in the log during application bootstrap. Make sure to disable the development mode before deploying to production!

Web application

For any web application, set the Servlet initialization parameter org.jboss.weld.development to true:

<web-app>
    <context-param>
        <param-name>org.jboss.weld.development</param-name>
        <param-value>true</param-value>
    </context-param>
</web-app>

WildFly

Since WildFly 10 it’s also possible to enable the Weld development mode globally (i.e. for all the applications deployed) by setting development-mode attribute to true:

/subsystem=weld:write-attribute(name=development-mode,value=true)

See also WildFly CDI Reference.

Weld SE

For a Java SE application, set the system property org.jboss.weld.development to true:

java -cp myCoolApp.jar -Dorg.jboss.weld.development=true com.foo.MyMain

or use the Weld.property() method:

org.jboss.weld.environment.se.Weld;

public static void main(String[] args) {
   Weld weld = new Weld().property("org.jboss.weld.development", true);
   try (WeldContainer container = weld.initialize()) {
      ...
   }
}

How does it actually work?

Probe collects CDI-related data from your application and then makes the data available through the REST API, eventually through the MXBean of name org.jboss.weld.probe:type=JsonData,context=ID where ID should be replaced with an idenfitier of an application.

Probe UI

Probe has also a web UI (single-page application) available at {webapp-context-path}/weld-probe (once your webapp starts), e.g. http://localhost:8080/weld-numberguess/weld-probe. By default, Probe also embeds a tiny information bar directly into the application’s HTML output. That makes it easy to navigate to Probe directly from the application anytime. Furthermore, if invocation tracking is enabled, the information bar helps navigate directly to the invocation tree related to the request that rendered the output.

  • The best place to start is probably the Beans view

  • You may also discover the observer methods declared by an extension

  • Monitor all the fired events and track which observer methods a particular event was delivered to

  • And more…​

We believe the UI is quite intuitive but feel free to ask questions on any channel (irc, gitter, mailing list, etc.).

Tip
 There are some configuration properties which allow to tune or disable Probe features, e.g. to restrict the set of components which will be monitored. See also Development Mode Configuration.

What if I don’t have a webapp?

Nothing is lost! JMX and weld-probe-client-adapter come to rescue. This "adapter" allows to reuse the default HTML UI even if there is no REST API available (non-web environments). The adapter either connects to a JMX server (Probe JMX support must be enabled) or loads data from an exported file (see also Does it work offline?), then starts an embedded Undertow webserver instance and exposes the default HTML client but using the data from the first step.

Does it work offline?

Sometimes it’s not possible to inspect a running system (e.g. due to security reasons). Probe allows to export the collected data and inspect it offline. There are two ways to export the data:

  1. Using REST API: HTTP GET {webapp-context-path}/weld-probe/export

  2. Configure Probe to export data after deployment (see also org.jboss.weld.probe.exportDataAfterDeployment property in Development Mode Configuration)

And now use the weld-probe-client-adapter again:

java -jar weld-probe-client-adapter-1.0.0.Final-shaded.jar /home/weld/weld-probe-export.zip