using properties within the properties file

Question

I apologize for the title.. i couldn\'t find a better way to explain the situation.

I use to load properties file using a Property class as described in the URL http

Answer 1

I've done something like this and it isn't that difficult, you simply subclass the Properties class and implement your own getProperty method, check for a pattern and replace it if necessary.

//this makes the pattern ${sometext}
static public final String JAVA_CONFIG_VARIABLE = "\\$\\{(.*)\\}";

@Override
public String getProperty(String key)
{
    String val = super.getProperty(key);
    if( val != null && val.indexOf("${") != -1 )
    {
        //we have at least one replacable parm, let's replace it
        val = replaceParms(val);
    }
    return val;
 }

 public final String replaceParms(String in)
 {
     if(in == null) return null;
     //this could be precompiled as Pattern is supposed to be thread safe
     Pattern pattern = Pattern.compile(JAVA_CONFIG_VARIABLE);
     Matcher matcher = pattern.matcher(in);
     StringBuffer buf = new StringBuffer();
     while (matcher.find())
     {
         String replaceStr = matcher.group(1);
         String prop = getProperty(replaceStr);   
         //if it isn't in our properties file, check if it is a system property
         if (prop == null )
             prop = System.getProperty(replaceStr);
         if( prop == null )
         {
            System.out.printf("Failed to find property '%s' for '%s'\n", replaceStr, in);
         }
         else
         {
           matcher.appendReplacement(buf, prop);
         } 
     }
     matcher.appendTail(buf);
     String result = buf.toString();
     return result;
 }