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• WatchDir.java

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com.njzxw.compress_maven_plugin.util.WatchDir Maven / Gradle / Ivy

package com.njzxw.compress_maven_plugin.util;

import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.FileVisitor;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;

public class WatchDir {

    private final WatchService watcher;
    private final Map keys;
    private final boolean recursive;
    private boolean trace = false;

    @SuppressWarnings("unchecked")
    static  WatchEvent cast(WatchEvent event) {
        return (WatchEvent)event;
    }

    /**
     * Register the given directory with the WatchService
     */
    private void register(Path dir) throws IOException {
    	
        WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        
        if (trace) {
        	
            Path prev = keys.get(key);
            
            if (prev == null) {
            	
                System.out.format("register: %s\n", dir);
                
            } else {
            	
                if (!dir.equals(prev)) {
                	
                    System.out.format("update: %s -> %s\n", prev, dir);
                    
                }
            }
        }
        keys.put(key, dir);
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(final Path start) throws IOException {
        // register directory and sub-directories
        Files.walkFileTree(start, new FileVisitor() {
            @Override
            public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                throws IOException
            {
                register(dir);
                return FileVisitResult.CONTINUE;
            }

			@Override
			public FileVisitResult visitFile(Path file,
					BasicFileAttributes attrs) throws IOException {
				return null;
			}

			@Override
			public FileVisitResult visitFileFailed(Path file, IOException exc)
					throws IOException {
				return null;
			}

			@Override
			public FileVisitResult postVisitDirectory(Path dir, IOException exc)
					throws IOException {
				return null;
			}
        });
    }

    /**
     * 创建监控文件
     * @param dir
     * @param recursive
     * @throws IOException
     */
    WatchDir(Path dir, boolean recursive) throws IOException {
    	
        this.watcher = FileSystems.getDefault().newWatchService();
        
        this.keys = new HashMap();
        
        this.recursive = recursive;

        if (recursive) {
        	
            System.out.format("Scanning %s ...\n", dir);
            
            registerAll(dir);
            
            System.out.println("Done.");
            
        } else {
        	
            register(dir);
            
        }

        // enable trace after initial registration
        this.trace = true;
    }

    /**
     * Process all events for keys queued to the watcher
     */
    void processEvents() {
    	
        for (;;) {//这是个死循环

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

            Path dir = keys.get(key);
            
            if (dir == null) {
            	
                System.err.println("WatchKey not recognized!!");
                
                continue;
            }

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

                // TBD - provide example of how OVERFLOW event is handled
                if (kind == OVERFLOW) {
                	
                    continue;
                    
                }

                // Context for directory entry event is the file name of entry
                WatchEvent ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);

                // print out event
                System.out.format("%s: %s\n", event.kind().name(), child);

                // if directory is created, and watching recursively, then
                // register it and its sub-directories
                if (recursive && (kind == ENTRY_CREATE)) {
                    try {
                        if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                            registerAll(child);
                        }
                    } catch (IOException x) {
                        // ignore to keep sample readbale
                    }
                }
            }

            // reset key and remove from set if directory no longer accessible
            boolean valid = key.reset();
            if (!valid) {
                keys.remove(key);

                // all directories are inaccessible
                if (keys.isEmpty()) {
                    break;
                }
            }
        }
    }

    static void usage() {
        System.err.println("usage: java WatchDir [-r] dir");
        System.exit(-1);
    }
    
    public static void main(String[] args) throws IOException {
        // parse arguments

        // register directory and process its events
        Path dir = Paths.get("d:\\www");
        
        new WatchDir(dir, true).processEvents();
    }
}