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 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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 */

import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;

/**
 * Example monitors a specified directory for new files.
 * If a newly added file is a plain text file, the file can
 * be emailed to the appropriate alias.  The emailing details
 * are left to the reader.  What the example actually does is
 * print the details to standard out.
 */

public class Email {

    private final WatchService watcher;
    private final Path dir;

    /**
     * Creates a WatchService and registers the given directory
     */
    Email(Path dir) throws IOException {
        this.watcher = FileSystems.getDefault().newWatchService();
        dir.register(watcher, ENTRY_CREATE);
        this.dir = dir;
    }

    /**
     * Process all events for the key queued to the watcher.
     */
    void processEvents() {
        for (;;) {

            // wait for key to be signaled
            WatchKey key;
            try {
                key = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            for (WatchEvent<?> event: key.pollEvents()) {
                WatchEvent.Kind kind = event.kind();

                if (kind == OVERFLOW) {
                    continue;
                }

                //The filename is the context of the event.
                WatchEvent<Path> ev = (WatchEvent<Path>)event;
                Path filename = ev.context();

                //Verify that the new file is a text file.
                try {
                    Path child = dir.resolve(filename);
                    if (!Files.probeContentType(child).equals("text/plain")) {
                        System.err.format("New file '%s' is not a plain text file.%n", filename);
                        continue;
                    }
                } catch (IOException x) {
                    System.err.println(x);
                    continue;
                }

                //Email the file to the specified email alias.
                System.out.format("Emailing file %s%n", filename);
                //Details left to reader....
            }

            //Reset the key -- this step is critical if you want to receive
            //further watch events. If the key is no longer valid, the directory
            //is inaccessible so exit the loop.
            boolean valid = key.reset();
            if (!valid) {
                    break;
            }
        }
    }

    static void usage() {
        System.err.println("usage: java Email dir");
        System.exit(-1);
    }

    public static void main(String[] args) throws IOException {
        //parse arguments
        if (args.length < 1)
            usage();

        //register directory and process its events
        Path dir = Paths.get(args[0]);
        new Email(dir).processEvents();
    }
}