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

Author: poutsma

spring-core/src/main/java/org/springframework/core/codec/ResourceEncoder.java

@@ -17,7 +17,7 @@
 package org.springframework.core.codec;
 
 import java.io.IOException;
-import java.io.InputStream;
+import java.nio.channels.ReadableByteChannel;
 import java.util.Map;
 
 import reactor.core.publisher.Flux;
@@ -66,8 +66,8 @@ public boolean canEncode(ResolvableType elementType, MimeType mimeType, Map<Stri
 	protected Flux<DataBuffer> encode(Resource resource, DataBufferFactory dataBufferFactory,
 			ResolvableType type, MimeType mimeType, Map<String, Object> hints) throws IOException {
 
-		InputStream is = resource.getInputStream();
-		return DataBufferUtils.read(is, dataBufferFactory, bufferSize);
+		ReadableByteChannel channel = resource.readableChannel();
+		return DataBufferUtils.read(channel, dataBufferFactory, bufferSize);
 	}
 
 }

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

@@ -17,12 +17,14 @@
 package org.springframework.core.io;
 
 import java.io.File;
+import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
+import java.nio.channels.ReadableByteChannel;
 
 import org.springframework.util.ResourceUtils;
 
@@ -115,6 +117,22 @@ protected File getFile(URI uri) throws IOException {
 		return ResourceUtils.getFile(uri, getDescription());
 	}
 
+	/**
+	 * This implementation returns a FileChannel for the given URI-identified
+	 * resource, provided that it refers to a file in the file system.
+	 * @since 5.0
+	 * @see #getFile(URI)
+	 */
+	@Override
+	public ReadableByteChannel readableChannel() throws IOException {
+		if (isFile()) {
+			return new FileInputStream(getFile()).getChannel();
+		}
+		else {
+			return super.readableChannel();
+		}
+	}
+
 
 	@Override
 	public boolean exists() {

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

@@ -23,6 +23,8 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.nio.channels.Channels;
+import java.nio.channels.ReadableByteChannel;
 
 import org.springframework.core.NestedIOException;
 import org.springframework.util.Assert;
@@ -122,6 +124,15 @@ public File getFile() throws IOException {
 		throw new FileNotFoundException(getDescription() + " cannot be resolved to absolute file path");
 	}
 
+	/**
+	 * This implementation returns {@link Channels#newChannel(InputStream)} with the result of
+	 * {@link #getInputStream()}.
+	 */
+	@Override
+	public ReadableByteChannel readableChannel() throws IOException {
+		return Channels.newChannel(getInputStream());
+	}
+
 	/**
 	 * This implementation reads the entire InputStream to calculate the
 	 * content length. Subclasses will almost always be able to provide

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

@@ -24,6 +24,7 @@
 import java.io.OutputStream;
 import java.net.URI;
 import java.net.URL;
+import java.nio.channels.ReadableByteChannel;
 
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -168,6 +169,15 @@ public File getFile() {
 		return this.file;
 	}
 
+	/**
+	 * This implementation opens a FileChannel for the underlying file.
+	 * @see java.nio.channels.FileChannel
+	 */
+	@Override
+	public ReadableByteChannel readableChannel() throws IOException {
+		return new FileInputStream(this.file).getChannel();
+	}
+
 	/**
 	 * This implementation returns the underlying File's length.
 	 */

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

@@ -23,10 +23,12 @@
 import java.io.OutputStream;
 import java.net.URI;
 import java.net.URL;
+import java.nio.channels.ReadableByteChannel;
 import java.nio.file.Files;
 import java.nio.file.OpenOption;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
 
 import org.springframework.util.Assert;
 
@@ -194,6 +196,15 @@ public File getFile() throws IOException {
 		}
 	}
 
+	/**
+	 * This implementation opens a InputStream for the underlying file.
+	 * @see java.nio.file.spi.FileSystemProvider#newInputStream(Path, OpenOption...)
+	 */
+	@Override
+	public ReadableByteChannel readableChannel() throws IOException {
+		return Files.newByteChannel(this.path, StandardOpenOption.READ);
+	}
+
 	/**
 	 * This implementation returns the underlying File's length.
 	 */

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

@@ -18,8 +18,11 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URI;
 import java.net.URL;
+import java.nio.channels.Channels;
+import java.nio.channels.ReadableByteChannel;
 
 /**
  * Interface for a resource descriptor that abstracts from the actual
@@ -111,6 +114,19 @@ default boolean isFile() {
 	 */
 	File getFile() throws IOException;
 
+	/**
+	 * Return a {@link ReadableByteChannel}.
+	 * <p>It is expected that each call creates a <i>fresh</i> channel.
+	 * <p>The default implementation returns {@link Channels#newChannel(InputStream)} with the
+	 * result of {@link #getInputStream()}.
+	 * @return the byte channel for the underlying resource (must not be {@code null})
+	 * @throws IOException if the channel could not be opened
+	 * @since 5.0
+	 */
+	default ReadableByteChannel readableChannel() throws IOException {
+		return Channels.newChannel(getInputStream());
+	}
+
 	/**
 	 * Determine the content length for this resource.
 	 * @throws IOException if the resource cannot be resolved

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 @@
 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 @@
  * @author Nicholas Williams
  * @author Stephane Nicoll
  * @author Juergen Hoeller
+ * @author Arjen Poutsma
  */
 public class PathResourceTests {
 
@@ -287,4 +291,36 @@ public void directoryOutputStream() throws Exception {
 		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.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 String getDescription() {
 		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();
+			}
+		}
+	}
+
 }