FileCopypublic class FileCopy extends Object | 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. |
| Methods Summary |
|---|
| private static void | abort(java.lang.String msg)A convenience method to throw an exception
throw new IOException("FileCopy: " + msg);
| | public static void | copy(java.lang.String from_name, java.lang.String to_name)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.
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) { ; }
}
| | public static void | main(java.lang.String[] args)The main() method of the standalone program. Calls copy().
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()); }
}
|
|
