modules/blueprintweb.mdtext

Title: BlueprintWeb
<a name="BlueprintWeb"></a>
# BlueprintWeb

The Blueprint Web module makes it easy to use OSGi Blueprint as a dependency injection framework outside of OSGi containers such as inside any Servlet Engine. 

You can then use Blueprint as a small standards base alternative to the Spring Framework's XML dependency injection files.

<a name="BlueprintWeb-HowToUse"></a>
## How to use Blueprint Web

Just add the following to your web.xml

	  <listener>
	      <listener-class>org.apache.aries.blueprint.web.BlueprintContextListener</listener-class>
	  </listener>

This will then make your web application look in the classpath for all files called **META-INF/blueprint.xml**. Each one will then be loaded and created in a single BlueprintContainer for your web application.

Then in each jar or in the web application itself, just create a file called **src/main/resources/META-INF/blueprint.xml** which will then get included into jars or into your WAR.

If you wish to use a different name for the location of the blueprint files you can specify the **blueprintLocation** property as a context parameter as follows:

	  <context-param>
	      <param-name>blueprintLocation</param-name>
	      <param-value>META-INF/myName.xml</param-value>
	  </context-param>

<a name="BlueprintWeb-Configuraiton"></a>	
## Configuring blueprint through properties

Blueprint beans can be configured using the variable substitutions.
You need to declare the ext namespace and add the property placeholder bean in your blueprint xml

	<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
	           xmlns:ext="http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.2.0">
		<ext:property-placeholder>
	    	<ext:default-properties>
	        	<ext:property name="myProperty" value="defaultValue" />
	    	</ext:default-properties>
		</ext:property-placeholder>
		...
		<bean ...>
			<property name="myProperty" value="${myProperty}" />
		</bean>
	</blueprint>

The default value can be overriden by specifying an the blueprintProperties property as a context parameter in the web.xml:

	<context-param>
    	<param-name>blueprintProperties</param-name>
    	<param-value>myConfigFile.properties</param-value>
	</context-param>

The value of this parameter is a comma separated list of properties file loaded from the class loader.
In this case, adding a file called **src/main/resources/myConfigFile.properties** will do the trick.