Florian Hopf

Software Developer living in Singapore

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Spring in Action

26 Dec 2011

Sometimes it's comfortable to not be an absolute expert in a certain technology. This makes it really easy to learn new stuff, e.g. by profane methods like reading a book. Even if you are a Spring expert it is still likely that you will take something from the latest edition of Spring in Action by Craig Walls as it covers a wide range of topics. I haven't read one of the predecessors but people told me that those are even better.

Having finished the book recently I just wanted to take the time to write down two interesting small configuration features that I learned from it.

p-Namespace

A feature that I just didn't know before but seems to be quite useful is the p-Namespace. It's a namespace that is not backed by a schema and allows to configure beans in a really concise way. For example look at how a bean might be configured normally:

    <bean id="foo" class="foo.bar.Baz">
        <property name="myLongProperty" value="2"/>
        <property name="myStringProperty" value="Hallo"/>
    </bean>

The properties we'd like to set are children of the bean node. Netbeans comes with nice autocompletion support for the property names as you can see from the screenshot.

The p-Namespace is a more concise version where the property names itself become attributes of the bean node:

    <bean id="foo" class="foo.bar.Baz"
        p:myLongProperty="2" p:myStringProperty="Hallo"/>

See that Netbeans is also clever enough to offer code completion here as well.

I am not sure if I will use the short form of the p-Namespace a lot. A consistent use of the features in a project is quite important so I think if the short form is used it should be used everywhere in the project.

Accessing Constants

Sometimes you need to access some constants in your Spring configuration files. There are several ways to handle this, one of it using the util-Namespace:

<property name="day">
    <util:constant static-field="java.util.Calendar.WEDNESDAY"/>
</property>

Another way can be to use the Spring Expression Language to access it:

<property name="day" value="#{T(java.util.Calendar).WEDNESDAY}"/>

I think this can be used more commonly as the value doesn't need to be registered as a subnode. For example I had some problems using util:constant as key or value in a util:map. That would have been easy just using the EL version.

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