Implement #32

Author: cowtowncoder

release-notes/VERSION

@@ -5,6 +5,7 @@ NOTE: Annotations module will never contain changes in patch versions,
  only .0 releases can have changes.
 
 #31: Allow use of `@JsonPropertyOrder` for properties (not just classes)
+#32: Add `@JsonProperty.index`
 - Add `JsonFormat.Value#timeZoneAsString` (needed by Joda module)
 
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src/main/java/com/fasterxml/jackson/annotation/JsonProperty.java

@@ -31,6 +31,15 @@
      */
     public final static String USE_DEFAULT_NAME = "";
 
+    /**
+     * Marker value used to indicate that no index has been specified.
+     * Used as the default value as annotations do not allow "missing"
+     * values.
+     * 
+     * @since 2.4
+     */
+    public final static int INDEX_UNKNOWN = -1;
+    
     /**
      * Defines name of the logical property, i.e. JSON object field
      * name to use for the property. If value is empty String (which is the
@@ -59,6 +68,16 @@
      */
     boolean required() default false;
 
+    /**
+     * Property that indicates numerical index of this property (relative
+     * to other properties specified for the Object). This index
+     * is typically used by binary formats, but may also be useful
+     * for schema languages and other tools.
+     * 
+     * @since 2.4
+     */
+    int index() default INDEX_UNKNOWN;
+    
     /* NOTE: considering of adding ability to specify default
      * String value -- would work well for scalar types, most of
      * which can coerce from Strings. But won't add for 2.0 yet.