OPEN - issue BATCH-767: Update documentation for M2

http://jira.springframework.org/browse/BATCH-767

Updated the javadocs on ItemProcessor.

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/ItemProcessor.java

@@ -1,13 +1,26 @@
 package org.springframework.batch.item;
 
 /**
- * Interface for item transformations. If the return value is null it may be
- * ignored, so this interface is also able to act as a filter.
- * 
+ * <p>Interface for item transformation.  Given an item as input, this interface provides
+ * an extension point which allows for the application of business logic in an item 
+ * oriented processing scenario.  It should be noted that while it's possible to return
+ * a different type than the one provided, it's not strictly necessary.  Furthermore, 
+ * returning null indicates that the item should not be continued to be processed.</p>
+ *  
  * @author Robert Kasanicky
  * @author Dave Syer
  */
 public interface ItemProcessor<I, O> {
 
+	/**
+	 * Process the provided item, returning a potentially modified or new item for continued
+	 * processing.  If the returned result is null, it is assumed that processing of the item
+	 * should not continue.
+	 * 
+	 * @param item to be processed
+	 * @return potentially modified or new item for continued processing, null if processing of the 
+	 *  provided item should not continue.
+	 * @throws Exception
+	 */
 	O process(I item) throws Exception;
 }