1 files changed, 88 insertions, 0 deletions
diff --git a/velocity-engine-core/src/main/java/org/apache/velocity/app/event/InvalidReferenceEventHandler.java b/velocity-engine-core/src/main/java/org/apache/velocity/app/event/InvalidReferenceEventHandler.java
new file mode 100644
index 00000000..f02e09b6
--- /dev/null
+++ b/velocity-engine-core/src/main/java/org/apache/velocity/app/event/InvalidReferenceEventHandler.java
@@ -0,0 +1,88 @@
+package org.apache.velocity.app.event;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.apache.velocity.context.Context;
+import org.apache.velocity.util.introspection.Info;
+
+/**
+ * Event handler called when an invalid reference is encountered.  Allows
+ * the application to report errors or substitute return values. May be chained
+ * in sequence; the behavior will differ per method.
+ *
+ * <p>This feature should be regarded as experimental.
+ *
+ * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a>
+ * @version $Id$
+ * @since 1.5
+ */
+public interface InvalidReferenceEventHandler extends EventHandler
+{
+
+    /**
+     * Called when object is null or there is no getter for the given
+     * property.  Also called for invalid references without properties.
+     * invalidGetMethod() will be called in sequence for
+     * each link in the chain until the first non-null value is
+     * returned.
+     *
+     * @param context the context when the reference was found invalid
+     * @param reference string with complete invalid reference
+     * @param object the object referred to, or null if not found
+     * @param property the property name from the reference
+     * @param info contains template, line, column details
+     * @return substitute return value for missing reference, or null if no substitute
+     */
+    Object invalidGetMethod(Context context, String reference,
+                            Object object, String property, Info info);
+
+    /**
+     * Called when object is null or there is no setter for the given
+     * property.  invalidSetMethod() will be called in sequence for
+     * each link in the chain until a true value is returned.  It's
+     * recommended that false be returned as a default to allow
+     * for easy chaining.
+     *
+     * @param context the context when the reference was found invalid
+     * @param leftreference left reference being assigned to
+     * @param rightreference invalid reference on the right
+     * @param info contains info on template, line, col
+     *
+     * @return if true then stop calling invalidSetMethod along the
+     * chain.
+     */
+    boolean invalidSetMethod(Context context, String leftreference,
+                             String rightreference, Info info);
+
+    /**
+     * Called when object is null or the given method does not exist.
+     * invalidMethod() will be called in sequence for each link in
+     * the chain until the first non-null value is returned.
+     *
+     * @param context the context when the reference was found invalid
+     * @param reference string with complete invalid reference
+     * @param object the object referred to, or null if not found
+     * @param method the name of the (non-existent) method
+     * @param info contains template, line, column details
+     * @return substitute return value for missing reference, or null if no substitute
+     */
+    Object invalidMethod(Context context, String reference,
+                         Object object, String method, Info info);
+}