FileUtils.java

/**
 * This file is part of the JCROM project.
 * Copyright (C) 2008-2014 - All rights reserved.
 * Authors: Olafur Gauti Gudmundsson, Nicolas Dos Santos
 *
 * 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.jcrom.util.io;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

/**
 * General file manipulation utilities.
 */
public final class FileUtils {

    private FileUtils() {
    }

    //-----------------------------------------------------------------------
    /**
     * Opens a {@link FileInputStream} for the specified file, providing better
     * error messages than simply calling <code>new FileInputStream(file)</code>.
     * <p>
     * At the end of the method either the stream will be successfully opened,
     * or an exception will have been thrown.
     * <p>
     * An exception is thrown if the file does not exist.
     * An exception is thrown if the file object exists but is a directory.
     * An exception is thrown if the file exists but cannot be read.
     * 
     * @param file  the file to open for input, must not be <code>null</code>
     * @return a new {@link FileInputStream} for the specified file
     * @throws FileNotFoundException if the file does not exist
     * @throws IOException if the file object is a directory
     * @throws IOException if the file cannot be read
     * @since Commons IO 1.3
     */
    public static FileInputStream openInputStream(File file) throws IOException {
        if (file.exists()) {
            if (file.isDirectory()) {
                throw new IOException("File '" + file + "' exists but is a directory");
            }
            if (file.canRead() == false) {
                throw new IOException("File '" + file + "' cannot be read");
            }
        } else {
            throw new FileNotFoundException("File '" + file + "' does not exist");
        }
        return new FileInputStream(file);
    }

    /**
     * Reads the contents of a file into a String.
     * The file is always closed.
     *
     * @param file  the file to read, must not be <code>null</code>
     * @param encoding  the encoding to use, <code>null</code> means platform default
     * @return the file contents, never <code>null</code>
     * @throws IOException in case of an I/O error
     * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
     */
    public static String readFileToString(File file, String encoding) throws IOException {
        InputStream in = null;
        try {
            in = openInputStream(file);
            return IOUtils.toString(in, encoding);
        } finally {
            IOUtils.closeQuietly(in);
        }
    }

    /**
     * Reads the contents of a file into a byte array.
     * The file is always closed.
     *
     * @param file  the file to read, must not be <code>null</code>
     * @return the file contents, never <code>null</code>
     * @throws IOException in case of an I/O error
     * @since Commons IO 1.1
     */
    public static byte[] readFileToByteArray(File file) throws IOException {
        InputStream in = null;
        try {
            in = openInputStream(file);
            return IOUtils.toByteArray(in, file.length());
        } finally {
            IOUtils.closeQuietly(in);
        }
    }
}