在java中使用SAX解析大型XML [英] parsing large XML using SAX in java

问题描述

我正在尝试解析堆栈溢出数据转储，其中一个表名为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。在SAX中有没有办法让它只加载这些属性？如果有的话怎么样？我对SAX很新，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.

否则加载整个东西只会是纯粹的慢，一些属性不会被使用所以这是没用的。

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？如果可能的话我该如何做？

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

StartElementSax事件允许处理单个XML ELement。

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

在java代码中，您必须实现此方法

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，您都可以访问：

For every element, you can access:

1. 命名空间URI


2. XML QName


3. XML LocalName


4. 属性地图，在这里你可以提取你的两个属性...

1. Namespace URI
2. XML QName
3. XML LocalName
4. Map of attributes, here you can extract your two attributes...

请参阅特定deatils的ContentHandler实现。

see ContentHandler Implementation for specific deatils.

再见

更新：改进了流行的代码段。

UPDATED: improved prevous snippet.

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