[engine] implements new strategy for reference boolean evaluation

1) return false for a null object

2) return its value for a Boolean object, or the result of the getAsBoolean() method if it exists.

3) If directive.if.emptycheck = false (true by default), stop here and return true.

4) check for emptiness:
  - return whether an array is empty.
  - return whether isEmpty() is false (covers String and all Collection classes).
  - return whether length() is zero (covers CharSequence classes other than String).
  - returns whether size() is zero.
  - return whether a Number *strictly* equals zero.

5) check for emptiness after explicit conversion methods:
  - return whether the result of getAsString() is empty (and false for a null result) if it exists.
  - return whether the result of getAsNumber() *strictly* equals zero (and false for a null result) if it exists. 





git-svn-id: https://svn.apache.org/repos/asf/velocity/engine/trunk@1783739 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 7 insertions, 1 deletions

diff --git a/velocity-engine-core/src/main/java/org/apache/velocity/runtime/RuntimeConstants.java b/velocity-engine-core/src/main/java/org/apache/velocity/runtime/RuntimeConstants.java
index 2d1b5d91..b85c51f1 100644
--- a/velocity-engine-core/src/main/java/org/apache/velocity/runtime/RuntimeConstants.java
+++ b/velocity-engine-core/src/main/java/org/apache/velocity/runtime/RuntimeConstants.java
@@ -76,6 +76,12 @@ public interface RuntimeConstants
     String SKIP_INVALID_ITERATOR = "directive.foreach.skip.invalid";
 
     /**
+     * An empty object (string, collection) or zero number is false.
+     * @since 2.0
+     */
+    String CHECK_EMPTY_OBJECTS = "directive.if.emptycheck";
+    
+    /**
      * Starting tag for error messages triggered by passing a parameter not allowed in the #include directive. Only string literals,
      * and references are allowed.
      */
@@ -98,7 +104,7 @@ public interface RuntimeConstants
      * @since 1.7
      */
     String PROVIDE_SCOPE_CONTROL = "provide.scope.control";
-
+    
     /*
      * ----------------------------------------------------------------------
      *  R E S O U R C E   M A N A G E R   C O N F I G U R A T I O N