Cache Dup

I love how simple is it to configure and scale an Infinispan instance. My biggest bugbear with NoSQL in general is the problem of denormalisation, leading to lots of duplicate records which need to be “manually” kept in sync by the application. So I’ve been working on a wrapper around Infinispan that tracks what goes in and automatically maintains referential integrity across denormalised data. To demonstrate, here’s an extract from a passing test.

john = (Tennant)cacheDup.get(johnsId);
mark = (Tennant)cacheDup.get(marksId);
// John and Mark are tennants in the same house, in Hilldale
assert john.getHouse().getFullAddress()
assert john.getHouse().getSuburb().equals("Hilldale");
// But they're not the same instance in memory
// (eg: due to networking/persistence serialisation)
assert john.getHouse() != mark.getHouse();
// Oops, John just told me it's actually Lakedale, not Hilldale
cacheDup.put(johnsId, john);
// Mark's house has also been updated, automatically
mark = (Tennant)cacheDup.get(marksId);
assert mark.getHouse().getSuburb().equals("Lakedale");

In order for Cache Dup to be able to work with your “entities”, they need to follow these rules, which I’m trying to keep as simple as possible:

  • Have stable hashcode and equals implementations, based on immutable field(s). Ideally this should be something with business meaning, but could also just be a UUID.
  • Implement Serializable (otherwise you wouldn’t need Cache Dup)

The cacheDup variable in the previous example is an instance of CacheDupDelegator, which implements org.infinispan.Cache, delegating to a standard Infinispan Cache instance which you provide to its constructor. I plan on adding a CDI decorator to make this step unnecessary for CDI-managed Cache instances.

CacheDupDelegator cacheDup = new CacheDupDelegator(cache);

This is obviously very early days. Current limitations that I know of are:

  • List is the only type of collection supported
  • If an object contains (directly or indirectly) a reference to itself, a stack overflow will probably result.

All kinds of feedback welcome. My biggest hurdles with this are going to be things I don’t know I don’t know.

Seam Cron: Scheduling Portable Extension for CDI

Update: This has now made its way into Seam 3 proper, as Seam Cron. Unfortunately it won’t be available for the initial Seam 3.0 release, but will become available soonishly.

Introducing Web Beans Scheduling (now Weld Scheduling (Now Seam Cron)) – a way to run scheduled events in JBoss Weld, Seam 3 and possibly any JSR-299 implementation. It makes use of CDI’s typesafe event model for tying business logic to schedules. That is, you define your schedules using the provided qualifiers, which you apply to observer methods containing the business logic that you wish to be run at those times. In other words:

    public void onSchedule(@Observes @Scheduled("20 */2 * ? * *") CronEvent e) {
        // do something every 2 minutes, at 20 seconds past the minute.

The CDI container will fire the @Scheduled(“20 */2 * ? * *”) CronEvent at 20 seconds past every second minute, causing the onSchedule method to be executed each time. When CDI starts up with this module on the classpath, all observers of the CronEvent class are detected by the module using standard CDI APIs. The module then inspects each associated @Scheduled binding annotation and sets up a schedule to fire a CronEvent with that binding at the schedule found. Currently Quartz is used as the underlying scheduler.

One obvious shortcoming of this is that we’ve managed to hard-code scheduling information in our Java code. The answer to this is to define the schedule as a property in the file at the root of your classpath, for example:

# This schedule is named "" and runs every 2 minutes */2 * ? * *
# This schedule is named "after.hours" and runs in the wee hours every day
after.hours=0 0 2 ? * *

You can then observe that schedule like this:

    public void onNamedSchedule(@Observes @Scheduled("") CronEvent event) {
        // the schedule is defined in

This is getting better, but that “” String is still setting off some refactoring alarm bells. No worries, we can deal with this pretty easily using meta-annotations. We just create a custom qualifier like so:

@Target( { ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD, ElementType.TYPE })
public @interface AfterHours {}

And now we can observe the event in a typesafe manner, in as many places as we want throughout our codebase with all the benefits of code-completion and none of the refactoring headaches:

    public void onTypesafeSchedule(@Observes @AfterHours CronEvent e) {
        // do something after hours

There are also some built-in convenience events for regular schedules:

    public void everySecond(@Observes @Every Second second) {
        // this gets executed every second

    public void everyMinute(@Observes @Every Minute minute) {
        // this gets executed every minute

    public void everyHour(@Observes @Every Hour hour) {
        // this gets executed every hour

Note though that none of these built-in events will be scheduled, let alone fired, unless the module finds an observer for them on startup.

This project has been submitted to the Seam 3 sandbox (find it in seam/sandbox/modules). An early release of the Weld Scheduling module and Memory Grapher example app can be downloaded from here: WeldScheduling.tgz. They’re both built with Maven 2.0.10+. To run the example app, ‘mvn clean install‘ both projects (‘scheduling’ first, then ‘MemoryGrapher’) and then run ‘mvn -Drun install’ from inside MemoryGrapher. It uses the Weld SE extension to run it without an app server (it’s a Swing app).