我想写的功能来处理使用监视文件夹的媒体文件。甲骨文例如WatchDir演示如何知道什么时候有一个文件夹中的变化。但是这个问题是，当所有的媒体已经完成上传我不知道。因此，例如，当包含其中包含在不同的文件夹多个文件介质SD卡拖动到监视文件夹，我需要能够处理媒体一旦所有的文件和子文件夹都存在。媒体并不总是只存储在单个文件，但可以有附属文件，以便两组文件需要存在，以便正确地处理文件。任何人都可以建议我怎么能知道，所有的文件和子文件夹已经完成被复制到监视文件夹？
这是我的WatchDir的稍作修改的版本，包括日志记录：
public class WatchDir {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
@SuppressWarnings("unchecked")
static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)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 SimpleFileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
throws IOException
{
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
WatchDir(Path dir, boolean recursive) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
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() {
System.out.println("process event");
boolean processing = false;
for (;;) {
System.out.println("loop");
// wait for key to be signalled
WatchKey key;
try {
processing = false;
System.out.println("about to take");
key = watcher.take();
processing = true;
} catch (InterruptedException x) {
System.out.println("take interrupted");
return;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
for (WatchEvent<?> event: key.pollEvents()) {
System.out.println("poll");
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
System.out.println("Overflow");
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> 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 readable
System.out.println("ex: " + x.getMessage());
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
System.out.println("finished this set of files");
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
if (processing) {
System.out.println("processing files...");
} else {
System.out.println("not processing files");
}
System.out.println("End of loop\n\n");
}
}
static void usage() {
System.err.println("usage: java WatchDir [-r] dir");
System.exit(-1);
}
public static void main(String[] args) throws IOException {
// parse arguments
if (args.length == 0 || args.length > 2)
usage();
boolean recursive = false;
int dirArg = 0;
if (args[0].equals("-r")) {
if (args.length < 2)
usage();
recursive = true;
dirArg++;
}
// register directory and process its events
Path dir = Paths.get(args[dirArg]);
new WatchDir(dir, recursive).processEvents();
}
}
也许你不能这样做。按照doc，该WatchService仅供这些事件：
static WatchEvent.Kind<Path> ENTRY_DELETE Directory entry deleted. static WatchEvent.Kind<Path> ENTRY_MODIFY Directory entry modified. static WatchEvent.Kind<Object> OVERFLOW A special event to indicate that events may have been lost or discarded. ```
所以，你不会知道是否有新的文件被创建/复制到目录中。
也许还有你可以考虑一些解决方法：