add a cache for genericParamName

Author: kang-hl

src/main/java/org/apache/ibatis/reflection/ParamNameResolver.java

@@ -35,6 +35,15 @@ public class ParamNameResolver {
 
   public static final String GENERIC_NAME_PREFIX = "param";
 
+  public static final String[] GENERIC_NAME_CACHE = new String[255];
+
+  static {
+    // the max length of java method parameter list is 255
+    for (int i = 0; i < 255; i++) {
+      GENERIC_NAME_CACHE[i] = GENERIC_NAME_PREFIX + (i + 1);
+    }
+  }
+
   private final boolean useActualParamName;
 
   /**
@@ -132,7 +141,7 @@ public Object getNamedParams(Object[] args) {
       for (Map.Entry<Integer, String> entry : names.entrySet()) {
         param.put(entry.getValue(), args[entry.getKey()]);
         // add generic param names (param1, param2, ...)
-        final String genericParamName = GENERIC_NAME_PREFIX + (i + 1);
+        final String genericParamName = GENERIC_NAME_CACHE[i];
         // ensure not to overwrite parameter named with @Param
         if (!names.containsValue(genericParamName)) {
           param.put(genericParamName, args[entry.getKey()]);