Shared ambiguity instance

Author: nieqiurong

src/main/java/org/apache/ibatis/session/Configuration.java

@@ -1155,7 +1155,7 @@ public V put(String key, V value) {
         if (super.get(shortKey) == null) {
           super.put(shortKey, value);
         } else {
-          super.put(shortKey, (V) new Ambiguity(shortKey));
+          super.put(shortKey, (V) Ambiguity.INSTANCE);
         }
       }
       return super.put(key, value);
@@ -1177,13 +1177,16 @@ public V get(Object key) {
         throw new IllegalArgumentException(name + " does not contain value for " + key);
       }
       if (value instanceof Ambiguity) {
-        throw new IllegalArgumentException(((Ambiguity) value).getSubject() + " is ambiguous in " + name
+        throw new IllegalArgumentException(key + " is ambiguous in " + name
             + " (try using the full name including the namespace, or rename one of the entries)");
       }
       return value;
     }
 
     protected static class Ambiguity {
+
+      protected static Ambiguity INSTANCE = new Ambiguity("ambiguity");
+
       private final String subject;
 
       public Ambiguity(String subject) {