moved getInputStream() not-null requirement to InputStreamSource itself; removed misleading "throws IllegalStateException" declaration

Issue: SPR-9561

spring-core/src/main/java/org/springframework/core/io/AbstractResource.java

@@ -173,7 +173,7 @@ public abstract class AbstractResource implements Resource {
 	 * This implementation always returns <code>null</code>,
 	 * assuming that this resource type does not have a filename.
 	 */
-	public String getFilename() throws IllegalStateException {
+	public String getFilename() {
 		return null;
 	}
 

spring-core/src/main/java/org/springframework/core/io/InputStreamSource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2007 the original author or authors.
+ * Copyright 2002-2012 the original author or authors.
  * 
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,6 +47,7 @@ public interface InputStreamSource {
 	 * as JavaMail, which needs to be able to read the stream multiple times when
 	 * creating mail attachments. For such a use case, it is <i>required</i>
 	 * that each <code>getInputStream()</code> call returns a fresh stream.
+	 * @return the input stream for the underlying resource (must not be {@code null})
 	 * @throws IOException if the stream could not be opened
 	 * @see org.springframework.mail.javamail.MimeMessageHelper#addAttachment(String, InputStreamSource)
 	 */

spring-core/src/main/java/org/springframework/core/io/Resource.java

@@ -133,9 +133,4 @@ public interface Resource extends InputStreamSource {
 	 */
 	String getDescription();
 
-	/**
-	 * {@inheritDoc}
-	 * @return the input stream for the underlying resource (must not be {@code null}).
-	 */
-	public InputStream getInputStream() throws IOException;
 }