DefaultResourceLoader resolves writable FileUrlResource for "file:" URL

Issue: SPR-16140

Author: jhoeller

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

@@ -27,6 +27,7 @@
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.ResourceUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -160,7 +161,7 @@ else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
 			try {
 				// Try to parse the location as a URL...
 				URL url = new URL(location);
-				return new UrlResource(url);
+				return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
 			}
 			catch (MalformedURLException ex) {
 				// No URL -> resolve as resource path.

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

@@ -183,7 +183,7 @@ public File getFile() {
 	 */
 	@Override
 	public ReadableByteChannel readableChannel() throws IOException {
-		return FileChannel.open(getFile().toPath(), StandardOpenOption.READ);
+		return FileChannel.open(this.file.toPath(), StandardOpenOption.READ);
 	}
 
 	/**
@@ -192,7 +192,7 @@ public ReadableByteChannel readableChannel() throws IOException {
 	 */
 	@Override
 	public WritableByteChannel writableChannel() throws IOException {
-		return FileChannel.open(getFile().toPath(), StandardOpenOption.WRITE);
+		return FileChannel.open(this.file.toPath(), StandardOpenOption.WRITE);
 	}
 
 	/**

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

@@ -0,0 +1,101 @@
+/*
+ * Copyright 2002-2017 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.
+ * 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.
+ */
+
+package org.springframework.core.io;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.nio.channels.FileChannel;
+import java.nio.channels.WritableByteChannel;
+import java.nio.file.Files;
+import java.nio.file.StandardOpenOption;
+
+import org.springframework.util.ResourceUtils;
+
+/**
+ * Subclass of {@link UrlResource} which assumes file resolution, to the degree
+ * of implementing the {@link WritableResource} interface for it.
+ *
+ * <p>This is the class resolved by {@link DefaultResourceLoader} for a "file:..."
+ * URL location, allowing a downcast to {@link WritableResource} for it.
+ *
+ * <p>Alternatively, for direct construction from a {@link java.io.File} handle,
+ * consider using {@link FileSystemResource}. For an NIO {@link java.nio.file.Path},
+ * consider using {@link PathResource} instead.
+ *
+ * @author Juergen Hoeller
+ * @since 5.0.2
+ */
+public class FileUrlResource extends UrlResource implements WritableResource {
+
+	/**
+	 * Create a new {@code FileUrlResource} based on the given URL object.
+	 * <p>Note that this does not enforce "file" as URL protocol. If a protocol
+	 * is known to be resolvable to a file,
+	 * @param url a URL
+	 * @see ResourceUtils#isFileURL(URL)
+	 * @see #getFile()
+	 */
+	public FileUrlResource(URL url) {
+		super(url);
+	}
+
+	/**
+	 * Create a new {@code FileUrlResource} based on the given file location,
+	 * using the URL protocol "file".
+	 * <p>The given parts will automatically get encoded if necessary.
+	 * @param location the location (i.e. the file path within that protocol)
+	 * @throws MalformedURLException if the given URL specification is not valid
+	 * @see UrlResource#UrlResource(String, String)
+	 * @see ResourceUtils#URL_PROTOCOL_FILE
+	 */
+	public FileUrlResource(String location) throws MalformedURLException {
+		super(ResourceUtils.URL_PROTOCOL_FILE, location);
+	}
+
+
+	@Override
+	public boolean isWritable() {
+		try {
+			URL url = getURL();
+			if (ResourceUtils.isFileURL(url)) {
+				// Proceed with file system resolution
+				File file = getFile();
+				return (file.canWrite() && !file.isDirectory());
+			}
+			else {
+				return true;
+			}
+		}
+		catch (IOException ex) {
+			return false;
+		}
+	}
+
+	@Override
+	public OutputStream getOutputStream() throws IOException {
+		return Files.newOutputStream(getFile().toPath());
+	}
+
+	@Override
+	public WritableByteChannel writableChannel() throws IOException {
+		return FileChannel.open(getFile().toPath(), StandardOpenOption.WRITE);
+	}
+
+}