集册 Java实例教程 监视指定的目录以获取新文件

监视指定的目录以获取新文件

欢马劈雪     最近更新时间:2020-01-02 10:19:05

187
监视指定目录中是否有新文件到达

import java.nio.file.*;/** n o w j a v a . c o m - 时代Java 提 供 **/

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 {// 来自 nowjava

        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();

    }

}


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