修改Flume源码使taildir source支持递归（可配置）

Flume的source选哪个？
taildir source首选！
1.断点还原 positionFile可以记录偏移量
2.可配置文件组，里面使用正则表达式配置多个要监控的文件
就凭第一点其他的source都被比下去了！
这么好的taildir source有一点不完美，不能支持递归监控文件夹。
所以就只能修改源代码了……好玩，我喜欢~

改源码，先读源码

Flume的taildir source启动会调用start()方法作初始化，里面创建一个ReliableTaildirEventReader,这里用到了建造者模式

@Override
public synchronized void start() {
    logger.info("{} TaildirSource source starting with directory: {}", getName(), filePaths);
    try {
        reader = new ReliableTaildirEventReader.Builder()
                .filePaths(filePaths)
                .headerTable(headerTable)
                .positionFilePath(positionFilePath)
                .skipToEnd(skipToEnd)
                .addByteOffset(byteOffsetHeader)
                .cachePatternMatching(cachePatternMatching)
                .recursive(isRecursive)
                .annotateFileName(fileHeader)
                .fileNameHeader(fileHeaderKey)
                .build();
    } catch (IOException e) {
        throw new FlumeException("Error instantiating ReliableTaildirEventReader", e);
    }
    idleFileChecker = Executors.newSingleThreadScheduledExecutor(
            new ThreadFactoryBuilder().setNameFormat("idleFileChecker").build());
    idleFileChecker.scheduleWithFixedDelay(new idleFileCheckerRunnable(),
            idleTimeout, checkIdleInterval, TimeUnit.MILLISECONDS);

    positionWriter = Executors.newSingleThreadScheduledExecutor(
            new ThreadFactoryBuilder().setNameFormat("positionWriter").build());
    positionWriter.scheduleWithFixedDelay(new PositionWriterRunnable(),
            writePosInitDelay, writePosInterval, TimeUnit.MILLISECONDS);

    super.start();
    logger.debug("TaildirSource started");
    sourceCounter.start();
}

taildir source属于PollableSource，

/**
 * A {@link Source} that requires an external driver to poll to determine
 * whether there are {@linkplain Event events} that are available to ingest
 * from the source.
 *
 * @see org.apache.flume.source.EventDrivenSourceRunner
 */
public interface PollableSource extends Source {
    ...

这段注释的意思是PollableSource是需要一个外部驱动去查看有没有需要消费的事件，从而拉取事件，讲白了就是定时拉取。所以flume也不一定是真正实时的，只是隔一会儿不停地来查看事件而已。(与之相应的是另一种EventDrivenSourceRunner)
那么taildir source在定时拉取事件的时候是调用的process方法

@Override
public Status process() {
    Status status = Status.READY;
    try {
        existingInodes.clear();
        existingInodes.addAll(reader.updateTailFiles());
        for (long inode : existingInodes) {
            TailFile tf = reader.getTailFiles().get(inode);
            if (tf.needTail()) {
                tailFileProcess(tf, true);
            }
        }
        closeTailFiles();
        try {
            TimeUnit.MILLISECONDS.sleep(retryInterval);
        } catch (InterruptedException e) {
            logger.info("Interrupted while sleeping");
        }
    } catch (Throwable t) {
        logger.error("Unable to tail files", t);
        status = Status.BACKOFF;
    }
    return status;
}

重点就是下面这几行

existingInodes.addAll(reader.updateTailFiles());
for (long inode : existingInodes) {
  TailFile tf = reader.getTailFiles().get(inode);
  if (tf.needTail()) {
    tailFileProcess(tf, true);
  } 
}

从reader.updateTailFiles()获取需要监控的文件，然后对每一个进行处理，查看最后修改时间，判定是否需要tail，需要tail就tail
那么进入reader.updateTailFiles()

for (TaildirMatcher taildir : taildirCache) {
      Map<String, String> headers = headerTable.row(taildir.getFileGroup());

      for (File f : taildir.getMatchingFiles()) {
        long inode = getInode(f);
        TailFile tf = tailFiles.get(inode);
        if (tf == null || !tf.getPath().equals(f.getAbsolutePath())) {
          long startPos = skipToEnd ? f.length() : 0;
          tf = openFile(f, headers, inode, startPos);

遍历每一个正则表达式匹配对应的匹配器，每个匹配器去获取匹配的文件！taildir.getMatchingFiles()

List<File> getMatchingFiles() {
    long now = TimeUnit.SECONDS.toMillis(
            TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis()));
    long currentParentDirMTime = parentDir.lastModified();
    List<File> result;

    // calculate matched files if
    // - we don't want to use cache (recalculate every time) OR
    // - directory was clearly updated after the last check OR
    // - last mtime change wasn't already checked for sure
    //   (system clock hasn't passed that second yet)
    if (!cachePatternMatching ||
            lastSeenParentDirMTime < currentParentDirMTime ||
            !(currentParentDirMTime < lastCheckedTime)) {
        lastMatchedFiles = sortByLastModifiedTime(getMatchingFilesNoCache(isRecursive));
        lastSeenParentDirMTime = currentParentDirMTime;
        lastCheckedTime = now;
    }

    return lastMatchedFiles;
}

可以看到getMatchingFilesNoCache(isRecursive)就是获取匹配的文件的方法，也就是需要修改的方法了！
ps：这里的isRecursive是我加的~
点进去：

private List<File> getMatchingFilesNoCache() {
    List<File> result = Lists.newArrayList();
    try (DirectoryStream<Path> stream = Files.newDirectoryStream(parentDir.toPath(), fileFilter)) {
        for (Path entry : stream) {
            result.add(entry.toFile());
        }
    } catch (IOException e) {
        logger.error("I/O exception occurred while listing parent directory. " +
                "Files already matched will be returned. " + parentDir.toPath(), e);
    }
    return result;
}

源码是用了Files.newDirectoryStream(parentDir.toPath(), fileFilter))，将父目录下符合正则表达式的文件都添加到一个迭代器里。（这里还用了try (...)的语法糖）

---

找到地方了，开始改！

我在这个getMatchingFilesNoCache()方法下面下了一个重载的方法, 可增加扩展性：

private List<File> getMatchingFilesNoCache(boolean recursion) {
    if (!recursion) {
        return getMatchingFilesNoCache();
    }
    List<File> result = Lists.newArrayList();
    // 使用非递归的方式遍历文件夹
    Queue<File> dirs = new ArrayBlockingQueue<>(10);
    dirs.offer(parentDir);
    while (dirs.size() > 0) {
        File dir = dirs.poll();
        try {
            DirectoryStream<Path> stream = Files.newDirectoryStream(dir.toPath(), fileFilter);
            stream.forEach(path -> result.add(path.toFile()));
        } catch (IOException e) {
            logger.error("I/O exception occurred while listing parent directory. " +
                    "Files already matched will be returned. (recursion)" + parentDir.toPath(), e);
        }
        File[] dirList = dir.listFiles();
        assert dirList != null;
        for (File f : dirList) {
            if (f.isDirectory()) {
                dirs.add(f);
            }
        }
    }
    return result;
}

我使用了非递归的方式遍历文件夹，就是树到队列的转换。
到这里，核心部分就改完了。接下来要处理这个recursion的参数

---

华丽的分割线后，顺腾摸瓜！

一路改构造方法，添加这个参数，最终参数从哪来呢？
flume的source启动时会调用configure方法，将Context中的内容配置进reader等对象中。
isRecursive = context.getBoolean(RECURSIVE, DEFAULT_RECURSIVE);
context从TaildirSourceConfigurationConstants中获取配置名和默认值

  /**
   * Whether to support recursion. */
  public static final String RECURSIVE = "recursive";
  public static final boolean DEFAULT_RECURSIVE = false;

这里的recursive也就是flume配置文件里配置项了

# Whether to support recusion
a1.sources.r1.recursive = true

大功告成，打包试试！

用maven只对这一个module打包。我把这个module的pom改了下artifactId，加上了自己名字作个纪念，哈哈
可惜pom里面不能写中文……

<groupId>org.apache.flume.flume-ng-sources</groupId>
<artifactId>flume-taildir-source-recursive-by-Wish000</artifactId>
<name>Flume Taildir Source</name>

执行package将其放在flume的lib下，替换原来的flume-taildir-source***.jar
启动，测试，成功！

具体代码见GitHub地址：https://github.com/Wish000/me...