Implement copy-on-write of the wrapped map.

src/helma/util/WrappedMap.java

@@ -19,6 +19,7 @@ package helma.util;
 import java.util.Map;
 import java.util.Set;
 import java.util.Collection;
+import java.util.HashMap;
 
 /**
  *  A Map that wraps another map and can be set to read-only.
@@ -31,6 +32,12 @@ public class WrappedMap implements Map {
     // is this map readonly?
     boolean readonly = false;
 
+    // isolate changes from the wrapped map?
+    boolean copyOnWrite = false;
+
+    public final static int READ_ONLY = 1;
+    public final static int COPY_ON_WRITE = 2;
+
     /**
      *  Constructor
      */
@@ -42,6 +49,18 @@ public class WrappedMap implements Map {
         wrapped = map;
     }
 
+    /**
+     *  Constructor
+     */
+    public WrappedMap(Map map, int mode) {
+        this(map);
+        if (mode == READ_ONLY) {
+            readonly = true;
+        } else if (mode == COPY_ON_WRITE) {
+            copyOnWrite = true;
+        }
+    }
+
     /**
      *  Set the readonly flag on or off
      */
@@ -56,6 +75,20 @@ public class WrappedMap implements Map {
         return readonly;
     }
 
+    /**
+     *  Set the copyOnWrite flag on or off
+     */
+    public void setCopyOnWrite(boolean cow) {
+        copyOnWrite = cow;
+    }
+
+    /**
+     *  Is this map copyOnWrite?
+     */
+    public boolean isCopyOnWrite() {
+        return copyOnWrite;
+    }
+
     // Methods from interface java.util.Map -
     // these are just proxies to the wrapped map, except for
     // readonly checks on modifiers.
@@ -86,6 +119,10 @@ public class WrappedMap implements Map {
         if (readonly) {
             throw new RuntimeException("Attempt to modify readonly map");
         }
+        if (copyOnWrite) {
+            wrapped = new HashMap (wrapped);
+            copyOnWrite = false;
+        }
         return wrapped.put(key, value);
     }
 
@@ -93,6 +130,10 @@ public class WrappedMap implements Map {
         if (readonly) {
             throw new RuntimeException("Attempt to modify readonly map");
         }
+        if (copyOnWrite) {
+            wrapped = new HashMap (wrapped);
+            copyOnWrite = false;
+        }
         return wrapped.remove(key);
     }
 
@@ -100,6 +141,10 @@ public class WrappedMap implements Map {
         if (readonly) {
             throw new RuntimeException("Attempt to modify readonly map");
         }
+        if (copyOnWrite) {
+            wrapped = new HashMap (wrapped);
+            copyOnWrite = false;
+        }
         wrapped.putAll(t);
     }
 
@@ -107,6 +152,10 @@ public class WrappedMap implements Map {
         if (readonly) {
             throw new RuntimeException("Attempt to modify readonly map");
         }
+        if (copyOnWrite) {
+            wrapped = new HashMap (wrapped);
+            copyOnWrite = false;
+        }
         wrapped.clear();
     }