FileCopy.java Source code

Introduction

Here is the source code for FileCopy.java

Source

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
 */

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * This class is a standalone program to copy a file, and also defines a static
 * copy() method that other programs can use to copy files.
 */
public class FileCopy {
    /** The main() method of the standalone program. Calls copy(). */
    public static void main(String[] args) {
        if (args.length != 2) // Check arguments
            System.err.println("Usage: java FileCopy <source> <destination>");
        else {
            // Call copy() to do the copy; display any error messages
            try {
                copy(args[0], args[1]);
            } catch (IOException e) {
                System.err.println(e.getMessage());
            }
        }
    }

    /**
     * The static method that actually performs the file copy. Before copying the
     * file, however, it performs a lot of tests to make sure everything is as it
     * should be.
     */
    public static void copy(String from_name, String to_name) throws IOException {
        File from_file = new File(from_name); // Get File objects from Strings
        File to_file = new File(to_name);

        // First make sure the source file exists, is a file, and is readable.
        // These tests are also performed by the FileInputStream constructor
        // which throws a FileNotFoundException if they fail.
        if (!from_file.exists())
            abort("no such source file: " + from_name);
        if (!from_file.isFile())
            abort("can't copy directory: " + from_name);
        if (!from_file.canRead())
            abort("source file is unreadable: " + from_name);

        // If the destination is a directory, use the source file name
        // as the destination file name
        if (to_file.isDirectory())
            to_file = new File(to_file, from_file.getName());

        // If the destination exists, make sure it is a writeable file
        // and ask before overwriting it. If the destination doesn't
        // exist, make sure the directory exists and is writeable.
        if (to_file.exists()) {
            if (!to_file.canWrite())
                abort("destination file is unwriteable: " + to_name);
            // Ask whether to overwrite it
            System.out.print("Overwrite existing file " + to_file.getName() + "? (Y/N): ");
            System.out.flush();
            // Get the user's response.
            BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
            String response = in.readLine();
            // Check the response. If not a Yes, abort the copy.
            if (!response.equals("Y") && !response.equals("y"))
                abort("existing file was not overwritten.");
        } else {
            // If file doesn't exist, check if directory exists and is
            // writeable. If getParent() returns null, then the directory is
            // the current dir. so look up the user.dir system property to
            // find out what that is.
            String parent = to_file.getParent(); // The destination directory
            if (parent == null) // If none, use the current directory
                parent = System.getProperty("user.dir");
            File dir = new File(parent); // Convert it to a file.
            if (!dir.exists())
                abort("destination directory doesn't exist: " + parent);
            if (dir.isFile())
                abort("destination is not a directory: " + parent);
            if (!dir.canWrite())
                abort("destination directory is unwriteable: " + parent);
        }

        // If we've gotten this far, then everything is okay.
        // So we copy the file, a buffer of bytes at a time.
        FileInputStream from = null; // Stream to read from source
        FileOutputStream to = null; // Stream to write to destination
        try {
            from = new FileInputStream(from_file); // Create input stream
            to = new FileOutputStream(to_file); // Create output stream
            byte[] buffer = new byte[4096]; // To hold file contents
            int bytes_read; // How many bytes in buffer

            // Read a chunk of bytes into the buffer, then write them out,
            // looping until we reach the end of the file (when read() returns
            // -1). Note the combination of assignment and comparison in this
            // while loop. This is a common I/O programming idiom.
            while ((bytes_read = from.read(buffer)) != -1)
                // Read until EOF
                to.write(buffer, 0, bytes_read); // write
        }
        // Always close the streams, even if exceptions were thrown
        finally {
            if (from != null)
                try {
                    from.close();
                } catch (IOException e) {
                    ;
                }
            if (to != null)
                try {
                    to.close();
                } catch (IOException e) {
                    ;
                }
        }
    }

    /** A convenience method to throw an exception */
    private static void abort(String msg) throws IOException {
        throw new IOException("FileCopy: " + msg);
    }
}