These are some simple examples for JavaScript’s Promise object. Use it to make your asynchronous operations code more managable and avoid callback hells.

Google Cloud DNS service provides an interesting pay as you use pricing model. Announced in March 2014, Google Cloud DNS can only be managed via Google’s gcloud command line tool or REST APIs.

Spring Security has built-in “remember-me” authentication capability to remember the identity of a user (principle) between session.

However, default implementations for “persistent token” only support in-memory (for testing) and JDBC. I wanted to implement this with App Engine using Objectify for persistence.

All it takes is to implement a custom PersistentTokenRepository and configure Spring Security to use it. This post assumes that Spring Security has been configured to work correctly with App Engine.

I started with a Spring Java configuration that looks like this:

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@Configuration
public class MyConfig {
    MyService myService(Collection<RelatedService> relatedServices) {
        return new MyService(relatedServices);
    }
}

Basically Collection<RelatedService> is telling Spring to look for all beans matching the type of RelatedService and put them in a Collection for me to use in myService().

Then I wanted to make relatedServices an optional dependency. Ideally, I would like to be able to do something like this:

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@Configuration
public class MyConfig {
    // invalid use of @Autowired
    MyService myService(@Autowired(required=false) Collection<RelatedService> relatedServices) {
        return new MyService(relatedServices);
    }
}

However, @Autowired cannot annotate a parameter. This is what I end up doing.

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@Configuration
public class MyConfig {
    @Autowired(required=false)
    Collection<RelatedService> relatedServices

    MyService myService() {
        return new MyService(relatedServices);
    }
}

I would prefer to limit the visibility/scope of relatedServices within the method but it does not look possible.

The bower link feature makes it easy to change & test packages while using it as a dependency in other packages. If you are using Bower, you should be using this.

Google AppEngine (Java) provides ability to mock UserService in JUnit test cases with the help of LocalUserServiceTestConfig. However, switching user within a test case is not so simple.

Groovy has a unique quality that other dynamic/scripting languages does not – you can write plain Java code in a Groovy class.

This attribute makes it an excellent choice for Java developers trying to pick up this dynamic language – start by writing Java and ease into Groovy’s style as you practice.

Composing blog posts in Markdown is great but it would be even better if I can see how pages are rendered live. So, let’s have that.