Add Resource.readableChannel()

Added readableChannel() to Resource, which returns a
java.nio.ReadableByteChannel. The default implementation uses
Channels.newChannel() to create a channel based on what is returned from
getInputStream(). Subclasses have more effecient, file-based
implementations.

Issue: SPR-14698

spring-core/src/test/java/org/springframework/core/io/PathResourceTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -19,6 +19,9 @@ package org.springframework.core.io;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.net.URI;
+import java.nio.ByteBuffer;
+import java.nio.channels.ReadableByteChannel;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 
@@ -42,6 +45,7 @@ import static org.mockito.BDDMockito.*;
  * @author Nicholas Williams
  * @author Stephane Nicoll
  * @author Juergen Hoeller
+ * @author Arjen Poutsma
  */
 public class PathResourceTests {
 
@@ -287,4 +291,36 @@ public class PathResourceTests {
 		resource.getOutputStream();
 	}
 
+	@Test
+	public void getReadableByteChannel() throws Exception {
+		PathResource resource = new PathResource(TEST_FILE);
+		ReadableByteChannel channel = null;
+		try {
+			channel = resource.readableChannel();
+			ByteBuffer buffer = ByteBuffer.allocate((int) resource.contentLength());
+			channel.read(buffer);
+			buffer.rewind();
+			assertThat(buffer.limit(), greaterThan(0));
+		}
+		finally {
+			if (channel != null) {
+				channel.close();
+			}
+		}
+	}
+
+	@Test
+	public void getReadableByteChannelForDir() throws Exception {
+		PathResource resource = new PathResource(TEST_DIR);
+		thrown.expect(NoSuchFileException.class);
+		resource.readableChannel();
+	}
+
+	@Test
+	public void getReadableByteChannelDoesNotExist() throws Exception {
+		PathResource resource = new PathResource(NON_EXISTING_FILE);
+		thrown.expect(NoSuchFileException.class);
+		resource.readableChannel();
+	}
+
 }

spring-core/src/test/java/org/springframework/core/io/ResourceTests.java

@@ -21,6 +21,8 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.nio.ByteBuffer;
+import java.nio.channels.ReadableByteChannel;
 import java.util.HashSet;
 
 import org.junit.Ignore;
@@ -254,4 +256,22 @@ public class ResourceTests {
 		resource.contentLength();
 	}
 
+	@Test
+	public void testGetReadableByteChannel() throws IOException {
+		Resource resource = new FileSystemResource(getClass().getResource("Resource.class").getFile());
+		ReadableByteChannel channel = null;
+		try {
+			channel = resource.readableChannel();
+			ByteBuffer buffer = ByteBuffer.allocate((int) resource.contentLength());
+			channel.read(buffer);
+			buffer.rewind();
+			assertTrue(buffer.limit() > 0);
+		}
+		finally {
+			if (channel != null) {
+				channel.close();
+			}
+		}
+	}
+
 }