Implemented methods to obtain a checksum that signals changes in the object.

These checksums are included in Message Digests so that they change when
something in the Application changes.

src/helma/framework/core/Application.java

@@ -163,7 +163,7 @@ public final class Application implements IPathElement, Runnable {
 	dbDir = customDbDir;
 
 	// system-wide properties, default to null
-	Properties sysProps, sysDbProps;
+	SystemProperties sysProps, sysDbProps;
 	sysProps = sysDbProps = null;
 	home = null;
 
@@ -1251,6 +1251,15 @@ public final class Application implements IPathElement, Runnable {
     }
 
 
+    /**
+     *  Get a checksum that mirrors the state of this application in the sense 
+     *  that if anything in the applciation changes, the checksum hopefully will 
+     *  change, too.
+     */
+    public long getChecksum () {
+	return starttime + typemgr.getChecksum() + props.getChecksum();
+    }
+
     /**
      * Proxy method to get a property from the applications properties.
      */

src/helma/util/SystemProperties.java

@@ -15,7 +15,7 @@ public final class SystemProperties extends Properties {
 
     private Properties props;        // wrapped properties
     private Properties newProps;    // used while building up props
-    private Properties defaultProps;  // the default/fallback properties.
+    private SystemProperties defaultProps;  // the default/fallback properties.
     private File file;   // the underlying properties file from which we read.
     private long lastread, lastcheck, lastadd;  // time we last read/checked the underlying properties file
 
@@ -59,7 +59,7 @@ public final class SystemProperties extends Properties {
     /**
      *  Contstruct a properties object with the given default properties.
      */
-    public SystemProperties (Properties defaultProps) {
+    public SystemProperties (SystemProperties defaultProps) {
 	this (null, defaultProps);
     }
 
@@ -67,7 +67,7 @@ public final class SystemProperties extends Properties {
     /**
      *  Construct a properties object from a file name with the given default properties
      */
-    public SystemProperties (String filename, Properties defaultProps) {
+    public SystemProperties (String filename, SystemProperties defaultProps) {
 	// System.err.println ("building sysprops with file "+filename+" and node "+node);
 	this.defaultProps = defaultProps;
 	props = defaultProps == null ? new Properties () : new Properties (defaultProps);
@@ -83,6 +83,15 @@ public final class SystemProperties extends Properties {
 	    return lastadd;
 	return Math.max (file.lastModified (), lastadd);
     }
+    
+    /**
+     *  Return a checksum that changes when something in the properties changes.
+     */
+    public long getChecksum () {
+	if (defaultProps == null)
+	    return lastModified ();
+	return lastModified () + defaultProps.lastModified ();
+    }
 
     /**
      *  Private method to read file if it has been changed since the last time we did