問(wèn)題描述

我正在嘗試解析堆棧溢出數(shù)據(jù)轉(zhuǎn)儲(chǔ)，其中一張表名為 posts.xml，其中包含大約 1000 萬(wàn)個(gè)條目.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" />

我想解析這個(gè)xml，但只加載xml的某些屬性，即Id、PostTypeId、AcceptedAnswerId和其他2個(gè)屬性.SAX 中有沒有辦法讓它只加載這些屬性?如果有那怎么辦?我對(duì) SAX 很陌生，所以一些指導(dǎo)會(huì)有所幫助.

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.

否則加載整個(gè)東西會(huì)很慢，而且一些屬性無(wú)論如何都不會(huì)被使用，所以它是無(wú)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.

另一個(gè)問(wèn)題是是否可以跳轉(zhuǎn)到具有行 ID X 的特定行?如果可能的話，我該怎么做?

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?

推薦答案

StartElement" Sax Event 允許處理單個(gè) XML 元素.

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

在java代碼中你必須實(shí)現(xiàn)這個(gè)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
    }

 }

對(duì)于每個(gè)元素，您可以訪問(wèn):

For every element, you can access:

1. 命名空間 URI
2. XML QName
3. XML 本地名稱
4. 屬性圖，這里可以提取你的兩個(gè)屬性...

具體細(xì)節(jié)見 ContentHandler 實(shí)現(xiàn).

see ContentHandler Implementation for specific deatils.

再見

更新:改進(jìn)了之前的片段.

UPDATED: improved prevous snippet.

這篇關(guān)于在 Java 中使用 SAX 解析大型 XML的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！