added reflection based FactoryMap implementation

querydsl-core/src/main/java/com/mysema/query/util/FactoryMap.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2006 Mysema Ltd.
+ * All rights reserved.
+ * 
+ */
+package com.mysema.query.util;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * FactoryMap provides
+ *
+ * @author Timo Westkämper
+ * @version $Id: FactoryMap.java 3549 2008-06-10 17:56:47Z tiwe $
+ */
+public abstract class FactoryMap<V>{
+    
+    private final Map<List<?>,V> cache = new HashMap<List<?>,V>();
+    
+    private Method createMethod;
+    
+    public FactoryMap(){
+        for (Method m : getClass().getMethods()){
+            if (m.getName().equals("create")) createMethod = m;
+        }
+        if (createMethod == null){
+            throw new IllegalArgumentException("No create method given");
+        }else{
+            createMethod.setAccessible(true);
+        }
+    }
+    
+    @SuppressWarnings("unchecked")
+    public final V get(Object... args){
+        List<?> key = Arrays.asList(args);
+        if (cache.containsKey(key)){
+            return cache.get(key);
+        }else{
+            try {
+                V value = (V) createMethod.invoke(this, args);
+                cache.put(key, value);
+                return value;
+            } catch (Exception e) {
+                throw new RuntimeException("error", e);
+            }            
+        }
+    }
+    
+    public void clear(){
+        cache.clear();
+    }
+
+}