sábado, febrero 19, 2011

Basta Imaginar e Ele Está Partindo, Sereno e Lindo E Se a Gente Quiser....... Ele Vai Pousar.

This week Springsource people have uploaded the first milestone of Spring Framework 3.1.

For my diary work, Environment Abstraction is the best feature developed in current milestone.

Environment Abstraction allows us grouping bean definitions for activation in specific environments. For example you can define two data sources, where one will be used in testing (HSQL configuration) and the other one in production (PostgreSQL). I am sure that in your life using Spring, you have had uploaded by mistake the test database configuration into production code. Environment Abstraction tries to avoid this situation.

Now I have showed you a typical example, but you can also create a custom resolution of place-holders, so for example in test mode you use a properties file with log level property configured to TRACE, and in production the properties file configured to INFO.

Another example that I find it interesting is in acceptance tests. One of my tasks is design and develop planners for robots. In Unit Testing we are mocking the hardware interface with the robot. But in acceptance tests, instead of mocking the hardware interface, we inject an emulator interface, so you can see how a fictional software robot is moving in your screen and validate that all movements are correct visually.

In previous Spring versions, what we have is three Spring XML files, one for production, another one for acceptance tests, and one main file that imports one of both files, so depending on environment we import one file or another. As you can imagine this implies a manual process between production environment and testing environment; although is not tedious, can be omitted so having emulator hardware interface in production instead of driver interface to robot.

With Spring 3.1, only one file is required with both configurations, and depending on environment Spring loads the required beans.

An example of what I am explaining is:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     <beans profile="test, integration">
          <bean .../>
          <bean .../>
          <context:property-placeholder .../>
     <beans profile="production">
          <bean .../>
          <bean .../>
          <context:property-placeholder .../>
          <bean ..../>

First thing you will notice is that beans tag is still the root but also is self-nested. The first two nested beans have an attribute called profile. This attribute inform when the beans it contains are active. First beans are active when configured profile is test or integration, while second ones when production profile is active. The last one definition is always activated.

Continuously we are writing something like "depending on environment", and I suppose you are wondering how you specify that environment.

You have an environment variable called spring.profiles.active where you specify which is the current profile. For setting this variable you can use an export in case of *nix systems, or as parameter execution -Dspring.profiles.active, or in context.xml in case of web applications, ...

For example a valid environment definition should be:

export spring.profiles.active=test

In case you are using Java-based Container Configuration, @Profile("profileName") can be used in beans definition, for specifying profile name.

ApplicationContext has getEnvironment() method for specifying which profiles are activated.

AnnotationConfigApplicationContext ctx = ...

I have developed a simple example that have two classes, where one prints passed message in upper case, and the other one prints the message between sharp character. Depending on profile configuration it changes message format. Moreover the same example is provided but using Java-based Container Configuration.

Download code from my GITHub if you want to see the source code.

I hope you find this new feature as useful as I find, and more important, once you have configured your machines with required environment variable, you won't worry any more about changing configuration files.

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