Different environment variables per war in tomcat

Question

Is there a way to have different environment variables for different war files in tomcat? I am using a 3rd party war and need to have multiple deployments of the same war but with different environment variables (so it loads different configs).

Answer 1

Its easy if you run two instances of Tomcat independently. I'm assuming here you are talking about the OS environment variables.

You can also set properties in Tomcat for each war/web app. That would let you run two wars in one Tomcat instance. But that's not what you asked.

Answer 2

Ok, total crazy hack idea:

Implement a PropertyPlayHolderConfigurer (or use web.xml from Tomcat) for each app instance and load properties same name as you have for System.properties().

Then, create a delegate Properties class that contains both sets of properties. Then

Properties props = new DelegatingProperties(app1Props,app2Props)
System.setProperties(delegate);

public class DelegatingProperties extends Properties {

   private Properties app1Props;
   private Properties app2Props;

   public DelegatingProperties(Properties app1Props, Properties app2Props) {
        this.app1Props = app1Props;
        this.app2Props = app2Props;   
   }

   public String getProperty(String prop) {
       // begin crazy science
       String caller = new Throwable().getStackTrace()[0].getClassName();
       // this is where you get creative.
       // Do the System.setProperties() above so you can intercept calls to  
       //getProperty()
       // and find out the FQCN of the library class(es) that need these variable 
       // (use your debugger).
       // then implement the logic here to decide which of the 2 property sets you have
       // you will query to get the correct results     
   }
}

These are SYSTEM properties we are talking about and they are meant to apply system wide. Your library was probably developed when it was 1-app-1-jvm (or the developer is a tard which is also likely).

Can I atleast get props for creativity? :)