enhancement: allow properties file instead of init-params

[Will Berry]

Justification: If it were possible to specify a properties file in web.xml where this filter is configured, then web.xml could stay exactly the same for multiple deployments of a webapp with different CORS configuration (i.e. production and test). It is safer for automated deployment systems to generate an absent file than to replace one from the WAR; and while excluding web.xml from a WAR entirely is possible (with Maven anyway), it's not preferred.

I suggest something like this for web.xml:

<filter>
    <filter-name>CORS</filter-name>
    <filter-class>com.thetransactioncompany.cors.CORSFilter</filter-class>
    <init-param>
        <param-name>configuration.propertiesFile</param-name>
        <param-value>WEB-INF/config/corsFilter.properties</param-value>
    </init-param>
</filter>

And in the corsFilter.properties file:

cors.allowOrigin=http://mysite.com https://mysite.com
cors.allowSubdomains=true

And so on. Basically all the supported init-param names could occur in the properties file with the same semantics.

[Will Berry]

formatting

[Vladimir Dzhuvinov]

Thanks for submitting this proposal, I'll think about it.

Hybrid configuration - with init-params and properties - should actually work too.

[David Bellem]

I would prefer using an environment variable to indicate where to find the properties file. E.g. log4j does it this way.

[Vladimir Dzhuvinov]

The CORS configuration can now also be passed as a properties file which location is specified by a filter init parameter named "cors.configurationFile". See commits leading up to 6146293.

<filter>
    <filter-name>CORS</filter-name>
    <filter-class>com.thetransactioncompany.cors.CORSFilter</filter-class>
    <init-param>
        <param-name>cors.configurationFile</param-name>
        <param-value>WEB-INF/config/corsFilter.properties</param-value>
    </init-param>
</filter>