在 Java 中使用 SAX 解析大型 XML

问题描述

我正在尝试解析堆栈溢出数据转储，其中一张表名为 posts.xml，其中包含大约 1000 万个条目.示例 xml:

I am trying to parse the stack overflow data dump, one of the tables is called posts.xml which has around 10 million entry in it. Sample xml:

<?xml version="1.0" encoding="utf-8"?>
<posts>
  <row Id="1" PostTypeId="1" AcceptedAnswerId="26" CreationDate="2010-07-07T19:06:25.043" Score="10" ViewCount="1192" Body="&lt;p&gt;Now that the Engineer update has come, there will be lots of Engineers building up everywhere.  How should this best be handled?&lt;/p&gt;&#xA;" OwnerUserId="11" LastEditorUserId="56" LastEditorDisplayName="" LastEditDate="2010-08-27T22:38:43.840" LastActivityDate="2010-08-27T22:38:43.840" Title="In Team Fortress 2, what is a good strategy to deal with lots of engineers turtling on the other team?" Tags="&lt;strategy&gt;&lt;team-fortress-2&gt;&lt;tactics&gt;" AnswerCount="5" CommentCount="7" />
  <row Id="2" PostTypeId="1" AcceptedAnswerId="184" CreationDate="2010-07-07T19:07:58.427" Score="5" ViewCount="469" Body="&lt;p&gt;I know I can create a Warp Gate and teleport to Pylons, but I have no idea how to make Warp Prisms or know if there's any other unit capable of transporting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would in particular like this to built remote bases in 1v1&lt;/p&gt;&#xA;" OwnerUserId="10" LastEditorUserId="68" LastEditorDisplayName="" LastEditDate="2010-07-08T00:16:46.013" LastActivityDate="2010-07-08T00:21:13.163" Title="What protoss unit can transport others?" Tags="&lt;starcraft-2&gt;&lt;how-to&gt;&lt;protoss&gt;" AnswerCount="3" CommentCount="2" />
  <row Id="3" PostTypeId="1" AcceptedAnswerId="56" CreationDate="2010-07-07T19:09:46.317" Score="7" ViewCount="356" Body="&lt;p&gt;Steam won't let me have two instances running with the same user logged in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does that mean I cannot run a dedicated server on a PC (for example, for Left 4 Dead 2) &lt;em&gt;and&lt;/em&gt; play from another machine?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to run the dedicated server without running steam? Is there a configuration option I'm missing?&lt;/p&gt;&#xA;" OwnerUserId="14" LastActivityDate="2010-07-07T19:27:04.777" Title="How can I run a dedicated server from steam?" Tags="&lt;steam&gt;&lt;left-4-dead-2&gt;&lt;dedicated-server&gt;&lt;account&gt;" AnswerCount="1" />
  <row Id="4" PostTypeId="1" AcceptedAnswerId="14" CreationDate="2010-07-07T19:11:05.640" Score="10" ViewCount="201" Body="&lt;p&gt;When I get to the insult sword-fighting stage of The Secret of Monkey Island, do I have to learn every single insult and comeback in order to beat the Sword Master?&lt;/p&gt;&#xA;" OwnerUserId="17" LastEditorUserId="17" LastEditorDisplayName="" LastEditDate="2010-07-08T21:25:04.787" LastActivityDate="2010-07-08T21:25:04.787" Title="Do I have to learn all of the insults and comebacks to be able to advance in The Secret of Monkey Island?" Tags="&lt;monkey-island&gt;&lt;adventure&gt;" AnswerCount="3" CommentCount="2" />

我想解析这个xml，但只加载xml的某些属性，即Id、PostTypeId、AcceptedAnswerId和其他2个属性.SAX 中有没有办法让它只加载这些属性?如果有那怎么办?我对 SAX 很陌生，所以一些指导会有所帮助.

I would like to parse this xml, but only load certain attributes of the xml, which are Id, PostTypeId, AcceptedAnswerId and other 2 attributes. Is there a way in SAX so that it only loads these attributes?? If there is then how? I am pretty new to SAX, so some guidance would help.

否则加载整个东西会很慢，而且一些属性无论如何都不会被使用，所以它是无用的.

Otherwise loading the whole thing would just be purely slow and some of the attributes won't be used anyways so it's useless.

另一个问题是是否可以跳转到具有行 ID X 的特定行?如果可能的话，我该怎么做?

One other question is that would it be possible to jump to a particular row that has a row Id X? If possible then how do I do this?

推荐答案

StartElement" Sax Event 允许处理单个 XML 元素.

"StartElement" Sax Event permits to process a single XML ELement.

在java代码中你必须实现这个方法

In java code you must implement this method

public void startElement(String uri, String localName,
    String qName, Attributes attributes)
    throws SAXException {

    if("row".equals(localName)) {
        //this code is executed for every xml element "row"
        String id = attributes.getValue("id");
        String PostTypeId = attributes.getValue("PostTypeId");
        String AcceptedAnswerId = attributes.getValue("AcceptedAnswerId");
        //others two
        // you have your att values for an "row" element
    }

 }

对于每个元素，您可以访问:

For every element, you can access:

1. 命名空间 URI
2. XML QName
3. XML 本地名称
4. 属性图，这里可以提取你的两个属性...

具体细节见 ContentHandler 实现.

see ContentHandler Implementation for specific deatils.

再见

更新:改进了之前的片段.

UPDATED: improved prevous snippet.

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