英文:
Updating fields only if file was modified
问题
我有一个包含一些配置数据的 JSON 文件。解析工作正常，但我正在尝试实现配置的实时更新。因此，我设置了一个定时器，每隔几秒钟执行该任务，而且一切都运行良好。然而，如果自从最新解析以来未对配置进行修改，我希望避免再次解析文件带来的开销。
我编写了以下代码来实现这一点，然而，尽管执行了this.timestamp = latestTimestamp;，但字段变量 timestamp 仍然保持为零，而 latestTimestamp 则保持着最新的时间戳。我很困惑，因为这对我来说毫无意义。我在这里漏掉了什么？
@NonNull private String configFilePath;
@Getter private JSONObject configuration;
private long timestamp = 0;
/**
* 更新字段
* @throws IOException 如果在打开/读取文件时发生错误
* @throws ParseException 如果解析 JSON 文件时发生错误
*/
public void update() throws IOException, ParseException {
long latestTimestamp = getLatestTimestamp(this.configFilePath);
if (this.timestamp == latestTimestamp)
return;
this.configuration = this.parse(this.configFilePath);
this.timestamp = latestTimestamp;
// 即使再次调用时文件未被修改，上述条件也会导致 `false`
// 因为 `this.timestamp` 在某种程度上仍然保持为 0
}
上述代码是一个简化版本。完整的类可以在这里找到。
英文:
I have a JSON file containing some configuration data. Parsing it works all well, but I am trying to achieve a live update of the configuration. Thus, I set a scheduler to do the task every few seconds, and it works all well either. However, if no modification was made to the configuration since the latest parsing, I want to avoid the overhead of parsing the file once again.
I have written the following code to achieve that, however the field variable timestamp remains at zero despite this.timestamp = latestTimestamp; is executed while latestTimestamp holds the latest timestamp. I am confused now as it makes absolutely no sense to me. What am I missing here?
@NonNull private String configFilePath;
@Getter private JSONObject configuration;
private long timestamp = 0;
/**
* update the fields
* @throws IOException if an error occurred while opening / reading the file
* @throws ParseException if an error occurred parsing the JSON file
*/
public void update() throws IOException, ParseException {
long latestTimestamp = getLatestTimestamp(this.configFilePath);
if (this.timestamp == latestTimestamp)
return;
this.configuration = this.parse(this.configFilePath);
this.timestamp = latestTimestamp;
// the above condition results in `false` when called again despite file is not modified
// because this.timestamp somehow remains 0
}
The above code is a simplified version. The complete Class can be found here.
答案1
得分: 1
所以我认为 ""the field variable timestamp remains at zero" 只有在您的调度程序创建了一个新对象 JSONUpdater 的情况下才可能发生，这会将 timestamp 变量再次重置为0。尝试将其设置为 Singleton。
英文:
So I think "the field variable timestamp remains at zero" is only possible if your scheduler is creating a new object of your class JSONUpdater, which resets the timestamp variable to 0 again. Try making it Singleton.
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