/*
 * Copyright 2002-2018 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.lang.Nullable;
import org.springframework.util.ResourceUtils;

Subclass of UrlResource which assumes file resolution, to the degree of implementing the WritableResource interface for it. This resource variant also caches resolved File handles from getFile(). 
This is the class resolved by DefaultResourceLoader for a "file:..." URL location, allowing a downcast to WritableResource for it. 
Alternatively, for direct construction from a File handle or NIO Path, consider using FileSystemResource. 
Author:
Juergen Hoeller
Since:
5.0.2/**
 * Subclass of {@link UrlResource} which assumes file resolution, to the degree
 * of implementing the {@link WritableResource} interface for it. This resource
 * variant also caches resolved {@link File} handles from {@link #getFile()}.
 *
 * <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
 * or NIO {@link java.nio.file.Path}, consider using {@link FileSystemResource}.
 *
 * @author Juergen Hoeller
 * @since 5.0.2
 */
public class FileUrlResource extends UrlResource implements WritableResource {

	@Nullable
	private volatile File file;


	
Create a new FileUrlResource based on the given URL object. 
Note that this does not enforce "file" as URL protocol. If a protocol
is known to be resolvable to a file,
Params:
url – a URL
See Also:
ResourceUtils.isFileURL(URL)
getFile()/**
	 * 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 FileUrlResource based on the given file location, using the URL protocol "file". 
The given parts will automatically get encoded if necessary.
Params:
location – the location (i.e. the file path within that protocol)
Throws:
MalformedURLException – if the given URL specification is not valid
See Also:
UrlResource(String, String)
ResourceUtils.URL_PROTOCOL_FILE/**
	 * 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 File getFile() throws IOException {
		File file = this.file;
		if (file != null) {
			return file;
		}
		file = super.getFile();
		this.file = file;
		return file;
	}

	@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);
	}

	@Override
	public Resource createRelative(String relativePath) throws MalformedURLException {
		if (relativePath.startsWith("/")) {
			relativePath = relativePath.substring(1);
		}
		return new FileUrlResource(new URL(getURL(), relativePath));
	}

}