对于它的价值，我已经破解了一个小的概念证明，它能够
- 检测监视目录中添加、修改和删除的文件，
- 显示每个更改的统一差异（添加/删除文件时也显示完整差异），
- 通过保留源目录的卷影副本来跟踪连续更改，
- 以用户定义的节奏（默认为 5 秒）工作，以免在短时间内打印太多小的差异，而是偶尔打印一些较大的差异。
有几个限制会成为生产环境中的障碍：
- 为了不使示例代码过于复杂，在创建影子目录时会在开始时复制子目录（因为我已经回收了现有的方法来创建深层目录副本），但在运行时会被忽略。仅监视监视目录正下方的文件以避免递归。
- 不满足您不使用外部库的要求，因为我真的想避免重新发明轮子以创建统一差异。
- 这个解决方案的最大优势——它能够检测到文本文件中任何地方的变化，不仅仅是在文件末尾
tail -f——也是它最大的缺点：每当一个文件发生变化时，它必须被完全影子复制，否则程序无法检测到随后的变化。因此，对于非常大的文件，我不推荐此解决方案。
如何构建：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>de.scrum-master.tools</groupId>
<artifactId>SO_WatchServiceChangeLocationInFile</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>com.googlecode.java-diff-utils</groupId>
<artifactId>diffutils</artifactId>
<version>1.3.0</version>
</dependency>
</dependencies>
</project>
源代码（抱歉，有点长）：
package de.scrum_master.app;
import difflib.DiffUtils;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.LinkedList;
import java.util.List;
import static java.nio.file.StandardWatchEventKinds.*;
public class FileChangeWatcher {
public static final String DEFAULT_WATCH_DIR = "watch-dir";
public static final String DEFAULT_SHADOW_DIR = "shadow-dir";
public static final int DEFAULT_WATCH_INTERVAL = 5;
private Path watchDir;
private Path shadowDir;
private int watchInterval;
private WatchService watchService;
public FileChangeWatcher(Path watchDir, Path shadowDir, int watchInterval) throws IOException {
this.watchDir = watchDir;
this.shadowDir = shadowDir;
this.watchInterval = watchInterval;
watchService = FileSystems.getDefault().newWatchService();
}
public void run() throws InterruptedException, IOException {
prepareShadowDir();
watchDir.register(watchService, ENTRY_CREATE, ENTRY_MODIFY, ENTRY_DELETE);
while (true) {
WatchKey watchKey = watchService.take();
for (WatchEvent<?> event : watchKey.pollEvents()) {
Path oldFile = shadowDir.resolve((Path) event.context());
Path newFile = watchDir.resolve((Path) event.context());
List<String> oldContent;
List<String> newContent;
WatchEvent.Kind<?> eventType = event.kind();
if (!(Files.isDirectory(newFile) || Files.isDirectory(oldFile))) {
if (eventType == ENTRY_CREATE) {
if (!Files.isDirectory(newFile))
Files.createFile(oldFile);
} else if (eventType == ENTRY_MODIFY) {
Thread.sleep(200);
oldContent = fileToLines(oldFile);
newContent = fileToLines(newFile);
printUnifiedDiff(newFile, oldFile, oldContent, newContent);
try {
Files.copy(newFile, oldFile, StandardCopyOption.REPLACE_EXISTING);
} catch (Exception e) {
e.printStackTrace();
}
} else if (eventType == ENTRY_DELETE) {
try {
oldContent = fileToLines(oldFile);
newContent = new LinkedList<>();
printUnifiedDiff(newFile, oldFile, oldContent, newContent);
Files.deleteIfExists(oldFile);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
watchKey.reset();
Thread.sleep(1000 * watchInterval);
}
}
private void prepareShadowDir() throws IOException {
recursiveDeleteDir(shadowDir);
Runtime.getRuntime().addShutdownHook(
new Thread() {
@Override
public void run() {
try {
System.out.println("Cleaning up shadow directory " + shadowDir);
recursiveDeleteDir(shadowDir);
} catch (IOException e) {
e.printStackTrace();
}
}
}
);
recursiveCopyDir(watchDir, shadowDir);
}
public static void recursiveDeleteDir(Path directory) throws IOException {
if (!directory.toFile().exists())
return;
Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
Files.delete(file);
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
Files.delete(dir);
return FileVisitResult.CONTINUE;
}
});
}
public static void recursiveCopyDir(final Path sourceDir, final Path targetDir) throws IOException {
Files.walkFileTree(sourceDir, new SimpleFileVisitor<Path>() {
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
Files.copy(file, Paths.get(file.toString().replace(sourceDir.toString(), targetDir.toString())));
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
Files.createDirectories(Paths.get(dir.toString().replace(sourceDir.toString(), targetDir.toString())));
return FileVisitResult.CONTINUE;
}
});
}
private static List<String> fileToLines(Path path) throws IOException {
List<String> lines = new LinkedList<>();
String line;
try (BufferedReader reader = new BufferedReader(new FileReader(path.toFile()))) {
while ((line = reader.readLine()) != null)
lines.add(line);
}
catch (Exception e) {}
return lines;
}
private static void printUnifiedDiff(Path oldPath, Path newPath, List<String> oldContent, List<String> newContent) {
List<String> diffLines = DiffUtils.generateUnifiedDiff(
newPath.toString(),
oldPath.toString(),
oldContent,
DiffUtils.diff(oldContent, newContent),
3
);
System.out.println();
for (String diffLine : diffLines)
System.out.println(diffLine);
}
public static void main(String[] args) throws IOException, InterruptedException {
String watchDirName = args.length > 0 ? args[0] : DEFAULT_WATCH_DIR;
String shadowDirName = args.length > 1 ? args[1] : DEFAULT_SHADOW_DIR;
int watchInterval = args.length > 2 ? Integer.getInteger(args[2]) : DEFAULT_WATCH_INTERVAL;
new FileChangeWatcher(Paths.get(watchDirName), Paths.get(shadowDirName), watchInterval).run();
}
}
我建议使用默认设置（例如，使用名为“watch-dir”的源目录）并使用它一段时间，在编辑器中创建和编辑一些文本文件时观察控制台输出。它有助于理解软件的内部机制。如果出现问题，例如在一个 5 秒的节奏内，一个文件被创建但又很快又被删除，没有什么可以复制或比较，所以程序只会打印一个堆栈跟踪到System.err.