JAVA:使用 XmlStreamReader 收集 xml 标签的字节偏移量 [英] JAVA: gathering byte offsets of xml tags using an XmlStreamReader

问题描述

有没有办法使用 XMLStreamReader 准确地收集 xml 标签的字节偏移量?

Is there a way to accurately gather the byte offsets of xml tags using the XMLStreamReader?

我有一个需要随机访问的大型 xml 文件.我不想将整个内容写入数据库，而是希望使用 XMLStreamReader 运行一次以收集重要标签的字节偏移量，然后能够使用 RandomAccessFile 稍后检索标签内容.

I have a large xml file that I require random access to. Rather than writing the whole thing to a database, I would like to run through it once with an XMLStreamReader to gather the byte offsets of significant tags, and then be able to use a RandomAccessFile to retrieve the tag content later.

XMLStreamReader 似乎没有办法跟踪字符偏移.相反，人们建议将 XmlStreamReader 附加到跟踪已读取字节数的读取器(例如 apache.commons.io 提供的 CountingInputStream)

XMLStreamReader doesn't seem to have a way to track character offsets. Instead people recommend attaching the XmlStreamReader to a reader that tracks how many bytes have been read (the CountingInputStream provided by apache.commons.io, for example)

例如:

CountingInputStream countingReader = new CountingInputStream(new FileInputStream(xmlFile)) ;
XMLStreamReader xmlStreamReader = xmlStreamFactory.createXMLStreamReader(countingReader, "UTF-8") ;


while (xmlStreamReader.hasNext()) {
    int eventCode = xmlStreamReader.next();

    switch (eventCode) {
        case XMLStreamReader.END_ELEMENT :
            System.out.println(xmlStreamReader.getLocalName() + " @" + countingReader.getByteCount()) ;
    }

}
xmlStreamReader.close();

不幸的是，一定有一些缓冲正在进行，因为上面的代码打印出几个标签的相同字节偏移量.是否有更准确的方法来跟踪 xml 文件中的字节偏移量(理想情况下不放弃正确的 xml 解析)?

Unfortunately there must be some buffering going on, because the above code prints out the same byte offsets for several tags. Is there a more accurate way of tracking byte offsets in xml files (ideally without resorting to abandoning proper xml parsing)?

推荐答案

您可以在 XMLStreamReader 上使用 getLocation()(或 XMLEvent.getLocation()，如果您使用 XMLEventReader)，但我记得在某处读到它不可靠并且精确的.看起来它给出了标签的端点，而不是起始位置.

You could use getLocation() on the XMLStreamReader (or XMLEvent.getLocation() if you use XMLEventReader), but I remember reading somewhere that it is not reliable and precise. And it looks like it gives the endpoint of the tag, not the starting location.

我也有类似的需求，需要精确地知道标签在文件中的位置，我正在查看其他解析器，看看是否有一种可以保证提供必要级别的位置精度的解析器.

I have a similar need to precisely know the location of tags within a file, and I'm looking at other parsers to see if there is one that guarantees to give the necessary level of location precision.

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