custom PropertySource for placeholders

[dlipofsky]

I have a need for my own property source (it gets its properties from a database rather than a file).
I've extended PropertySource and I am creating it in the XML config file.

<bean id="foobarPropertySource" class="com.example.FooBarPropertySource">
<constructor-arg name="name" value="foobarPS" />
<constructor-arg name="source" ref="foobar" />
</bean>
<bean class="org.springframework.context.support.Propert ySourcesPlaceholderConfigurer">
<property name="propertySources" value="#{foobarPropertySource.propertySources}" />
<property name="ignoreUnresolvablePlaceholders" value="true" />
</bean>

But it's not working how I want it to work. Ideally I'd like it to try and resolve using my
source then fall back to using system properties and environment if it doesn't
find a match. In this config it uses foobarPropertySource but does not fall back
to using the others. #{foobarPropertySource.propertySources} returns a
MutablePropertySources object that just contains my PropertySource.

I'd also like it to work for both <import /> and ordinary properties. I tried implementing
ApplicationContextInitializer<ConfigurableWebAppli cationContext> and adding that to web.xml.
I got that to work for <import /> but then it wasn't working for placeholders in ordinary properties.
What am I missing?

[dlipofsky]

I'll answer my own question

I created this class

public class SpringContextInitializer implements
        ApplicationContextInitializer<ConfigurableWebApplicationContext> {

    public void initialize(ConfigurableWebApplicationContext applicationContext) {
        MyPropertySource ps = new MyPropertySource();
        applicationContext.getEnvironment().getPropertySources().addFirst(ps);
    }
}

You can do addLast() instead if you prefer system and env to take precedence.

in web.xml I added

    <context-param>
        <param-name>contextInitializerClasses</param-name>
        <param-value>com.example.SpringContextInitializer</param-value>
    </context-param>

in my beans declaration file add

<context:property-placeholder ignore-unresolvable="true" />

The ApplicationContextInitializer is what is necessary to have this work for <import /> references. If you don't need that and your properties are in a standard properties file you don't need to do all this, you'll find easier examples elsewhere. If you leave out the last step this will only work for <import /> and all other placeholders will be ignored.
ignore-unresolvable="true" prevents errors when you can't find the placeholder (which may or may not be what you want).