KML marshal生成零长度文件 [英] KML marshal produces zero-length files

问题描述

在Java代码中，我生成一个Thread，它每秒从模拟器收集DIS数据包，尝试格式化KML输出。在我的Java代码中，我正在创建一个包含样式，地标和多边形的文档。每隔一秒我就可以看到marshalAPI例程确实用我的数据创建了一个KML文件。但是，随机有时会创建一个完整的文件，有时它会创建一个零长度文件。即使我关闭DIS数据包生成器并让我的Java代码仍然运行，它仍继续随机创建一个完整的文件，有时会创建一个零长度文件。当我将计时器从每秒更改为每10秒时，行为每10秒发生一次。

In Java code, I spawn a Thread which every second gathers DIS packets from a simulator, and tries to format KML output. In my Java code I am creating a Document, with Styles and Placemarks and Polygons. Once every second I can see that the "marshal" API routine does indeed create a KML file with my data. However, randomly sometimes it creates a complete file, and sometimes it creates a zero-length file. Even when I turn my DIS packet generator off, and leave my Java code still running, it continues to randomly create a complete file, and sometimes create a zero-length file. When I change my timer from every second to every 10 seconds, the behavior occurs every 10 seconds.

我尝试将marshal（）用于File对象和OutputStream宾语;同样奇怪的行为。

I tried using marshal() to a File object, and to an OutputStream object; Same weird behavior.

推荐答案

这可能是由于并发访问造成的。创建一个marshaller是一项昂贵的操作，需要时间，据我所知，marshallers不是线程安全的。我在Restlet中使用jaxb连接器，加上JAK，这是一个关于如何创建marshallers并以线程安全方式缓存它们的好例子：

It could be due to concurrent access. Creating a marshaller is an expensive operation, it takes time and as far as I know marshallers are not threadsafe. I use the jaxb connector in Restlet, coupled with JAK, and that's a good example on how to create marshallers and cache them in a threadsafe way:

/** Use thread identity to preserve safety of access to marshalers. */
private final ThreadLocal<javax.xml.bind.Marshaller> marshaller = new ThreadLocal<javax.xml.bind.Marshaller>() {

查看marshaller如何在同步方法中创建，然后存储在ThreadLocal变量中。

See there how the marshaller is created in a synchronized method and then stored in a ThreadLocal variable.

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