如何在程序里动态加载配置文件

flume的sink进程或者kafka的consumer进程，特定的时候需要读取配置文件，如提取指定的字段或过滤指定字段等。这种情况，若没有动态加载，则需要需改代码或配置文件，重启进程方能生效，十分不利于维护。最好的办法是让进程去监控配置文件的改动，然后动态的去读取其中的内容并应用到进程中去，从而达到动态修改。

方案就是启动一个单独线程去监控配置文件的最后修改时间，若发现有改动则重新加载。

代码如下：

public class ReloadThread extends Thread {

  private static final Logger log = LoggerFactory.getLogger(ReloadThread.class);

  private long lastSuccessfulReload;
  private File configureFile;
  public List selectedFields;

  public ReloadThread(File configureFile) {
    this.configureFile = configureFile;
    selectedFields = new ArrayList();
  }

  public String getSelectedFields() {
    StringBuilder sb = new StringBuilder();
    for (String item : selectedFields) {
      sb.append(item).append(",");
    }
    if (sb.length() > 0) {
      return (sb.substring(0, sb.length() - 1));
    } else {
      return "";
    }
  }

  @Override
  public void run() {
    while (true) {
      long time = System.currentTimeMillis();
      long lastModified = configureFile.lastModified();
      if (lastModified > lastSuccessfulReload
          && time > lastModified + KafkaUtil.ALLOC_RELOAD_WAIT_MS) {
        try {
          synchronized (selectedFields) {
            reloadConfigureFile(configureFile);
            log.info("Reload configuration file: " + getSelectedFields());
            lastSuccessfulReload = System.currentTimeMillis();
          }
        } catch (Exception ex) {
          log.error(
              "Failed to reload config file - will use existing configuration.",
              ex);
        }
      }
    }
  }

  public void reloadConfigureFile(File configureFile) {
    try {
      /** 判断文件是否存在 */
      if (configureFile.isFile() && configureFile.exists()) {
        InputStreamReader read = new InputStreamReader(
            new FileInputStream(configureFile));
        BufferedReader bufferedReader = new BufferedReader(read);
        String line;
        while ((line = bufferedReader.readLine()) != null) {
          if (!selectedFields.contains(line)) {
            selectedFields.add(line);
          }
        }
        read.close();
      } else {
        log.error("Failed to find file:" + configureFile.getAbsolutePath());
      }
    } catch (Exception e) {
      log.error("Failed to read file:" + configureFile.getAbsolutePath(), e);
    }
  }
}