NamespaceDynamicProperties

Prelude

The purpose of this namespace is to make it easier to configure PropertySource backed dynamic properties, as described in the dynamic properties wiki page.

Adding the namespace headers

Before using one of the service elements in your bean definition file, you will need to add the Impala service namespace declaration to the root element of the relevant Spring configuration files.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dynaprop="http://www.impalaframework.org/schema/dynamicproperties"
       xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.impalaframework.org/schema/dynamicproperties http://impala.googlecode.com/svn/schema/dynamic-properties.xsd">

Note the entry xmlns:dynaprop="http://www.impalaframework.org/schema/dynamicproperties" declares the Impala dynamic properties, and the entry http://www.impalaframework.org/schema/dynamicproperties http://impala.googlecode.com/svn/schema/dynamic-properties.xsd associates this with a schema location.

An example

All the dynamic properties elements have the same basic structure, so we'll consider a simple example using a BooleanPropertyValue.

To begin with, we need a PropertySource instance which will 'back' or sit behind the various property entries. The simplest of these is the StaticPropertiesPropertySource, which simply uses a wired-in java.util.Properties instance. Other implementations might use a database table, JMX, a dynamically modifiable file system property source, etc.

<bean id="propertySource" class="org.impalaframework.config.StaticPropertiesPropertySource">
    <property name="properties">
        <bean class = "org.springframework.beans.factory.config.PropertiesFactoryBean">
            <property name="location" value = "classpath:dynamic.properties"/>
        </bean>
    </property>
</bean>

The file dynamic.properties contains an entry as shown below:

boolean.property=true

Without the property namespace, a dynamic property entry might look as follows:

<bean id = "booleanProperty" class="org.impalaframework.config.FloatPropertyValue">
    <property name="name" value="boolean.property"/>
    <property name="propertySource" ref="propertySource"/>
</bean>

Using the namespace, it is shown as below:

<dynaprop:boolean id = "booleanProperty" name="boolean.property" propertySource="propertySource" />

Common elements

Each of the dynamic property elements have a common set of attributes:

• id: the id of the bean. Only required if the bean is used in a standalone way.
• name: the name of the property being accessed. In our example above, the name needs to be boolean.property to access

the associated value in the dynamic.properties file.

• propertySource: the backing PropertySource instances.

As of Impala 1.0.1 it will also be possible to set a default value for the entry, using a defaultValue attribute.

The elements

boolean

Creates an instance of BooleanPropertyValue which can be injected into a bean requiring dynamically updatable properties.

<property name="booleanPropertyValue">
    <dynaprop:boolean name="boolean.property"   propertySource="propertySource" />
</property>

date

Creates an instance of DatePropertyValue.

<property name="datePropertyValue">
    <dynaprop:date name="date.property" propertySource="propertySource" pattern="yyyy-MM-dd" />
</property>

double

Creates an instance of DoublePropertyValue.

<property name="doublePropertyValue">
    <dynaprop:double name="double.property" propertySource="propertySource" />
</property>

float

Creates an instance of FloatPropertyValue.

<property name="floatPropertyValue">
    <dynaprop:float name="float.property" propertySource="propertySource" />
</property>

int

Creates an instance of IntPropertyValue.

<property name="intPropertyValue">
    <dynaprop:int name="int.property" propertySource="propertySource" />
</property>

long

Creates an instance of LongPropertyValue.

<property name="longPropertyValue">
    <dynaprop:long name="long.property" propertySource="propertySource" />
</property>

string

Creates an instance of StringPropertyValue.

<property name="stringPropertyValue">
    <dynaprop:string name="string.property" propertySource="propertySource" />
</property>