如何在 Java 中解析大 (50 GB) XML 文件

2022-01-10 00:00:00 xml xml-parsing java sax

目前我正在尝试使用 SAX 解析器，但大约 3/4 的文件完全冻结了，我尝试分配更多内存等但没有得到任何改进.

Currently im trying to use a SAX Parser but about 3/4 through the file it just completely freezes up, i have tried allocating more memory etc but not getting any improvements.

有什么办法可以加快速度吗?更好的方法?

Is there any way to speed this up? A better method?

将其剥离，所以我现在有以下代码，当在命令行中运行时，它仍然没有我想要的那么快.

Stripped it to bare bones, so i now have the following code and when running in command line it still doesn't go as fast as i would like.

使用java -Xms-4096m -Xmx8192m -jar reader.jar"运行它，我得到超过文章 700000 附近的 GC 开销限制

Running it with "java -Xms-4096m -Xmx8192m -jar reader.jar" i get a GC overhead limit exceeded around article 700000

主要:

public class Read {
    public static void main(String[] args) {       
       pages = XMLManager.getPages();
    }
}

XML 管理器

public class XMLManager {
    public static ArrayList<Page> getPages() {

    ArrayList<Page> pages = null; 
    SAXParserFactory factory = SAXParserFactory.newInstance();

    try {

        SAXParser parser = factory.newSAXParser();
        File file = new File("..\enwiki-20140811-pages-articles.xml");
        PageHandler pageHandler = new PageHandler();

        parser.parse(file, pageHandler);
        pages = pageHandler.getPages();

    } catch (ParserConfigurationException e) {
        e.printStackTrace();
    } catch (SAXException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }


    return pages;
    }    
}

页面处理程序

public class PageHandler extends DefaultHandler{

    private ArrayList<Page> pages = new ArrayList<>();
    private Page page;
    private StringBuilder stringBuilder;
    private boolean idSet = false;

    public PageHandler(){
        super();
    }

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

        stringBuilder = new StringBuilder();

         if (qName.equals("page")){

            page = new Page();
            idSet = false;

        } else if (qName.equals("redirect")){
             if (page != null){
                 page.setRedirecting(true);
             }
        }
    }

     @Override
     public void endElement(String uri, String localName, String qName) throws SAXException {

         if (page != null && !page.isRedirecting()){

             if (qName.equals("title")){

                 page.setTitle(stringBuilder.toString());

             } else if (qName.equals("id")){

                 if (!idSet){

                     page.setId(Integer.parseInt(stringBuilder.toString()));
                     idSet = true;

                 }

             } else if (qName.equals("text")){

                 String articleText = stringBuilder.toString();

                 articleText = articleText.replaceAll("(?s)<ref(.+?)</ref>", " "); //remove references
                 articleText = articleText.replaceAll("(?s)\{\{(.+?)\}\}", " "); //remove links underneath headings
                 articleText = articleText.replaceAll("(?s)==See also==.+", " "); //remove everything after see also
                 articleText = articleText.replaceAll("\|", " "); //Separate multiple links
                 articleText = articleText.replaceAll("\n", " "); //remove new lines
                 articleText = articleText.replaceAll("[^a-zA-Z0-9- \s]", " "); //remove all non alphanumeric except dashes and spaces
                 articleText = articleText.trim().replaceAll(" +", " "); //convert all multiple spaces to 1 space

                 Pattern pattern = Pattern.compile("([\S]+\s*){1,75}"); //get first 75 words of text
                 Matcher matcher = pattern.matcher(articleText);
                 matcher.find();

                 try {
                     page.setSummaryText(matcher.group());
                 } catch (IllegalStateException se){
                     page.setSummaryText("None");
                 }
                 page.setText(articleText);

             } else if (qName.equals("page")){

                 pages.add(page);
                 page = null;

            }
        } else {
            page = null;
        }
     }

     @Override
     public void characters(char[] ch, int start, int length) throws SAXException {
         stringBuilder.append(ch,start, length); 
     }

     public ArrayList<Page> getPages() {
         return pages;
     }
}

推荐答案

您的解析代码可能工作正常，但是您正在加载的数据量可能太大而无法在 ArrayList.

Your parsing code is likely working fine, but the volume of data you're loading is probably just too large to hold in memory in that ArrayList.

您需要某种管道将数据传递到其实际目的地，而无需任何时间一次将其全部存储在内存中.

You need some sort of pipeline to pass the data on to its actual destination without ever store it all in memory at once.

我有时对这种情况所做的类似于以下情况.

What I've sometimes done for this sort of situation is similar to the following.

创建处理单个元素的接口:

Create an interface for processing a single element:

public interface PageProcessor {
    void process(Page page);
}

通过构造函数向 PageHandler 提供 this 的实现:

Supply an implementation of this to the PageHandler through a constructor:

public class Read  {
    public static void main(String[] args) {

        XMLManager.load(new PageProcessor() {
            @Override
            public void process(Page page) {
                // Obviously you want to do something other than just printing, 
                // but I don't know what that is...
                System.out.println(page);
           }
        }) ;
    }

}


public class XMLManager {

    public static void load(PageProcessor processor) {
        SAXParserFactory factory = SAXParserFactory.newInstance();

        try {

            SAXParser parser = factory.newSAXParser();
            File file = new File("pages-articles.xml");
            PageHandler pageHandler = new PageHandler(processor);

            parser.parse(file, pageHandler);

        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

将数据发送到此处理器而不是将其放入列表中:

Send data to this processor instead of putting it in the list:

public class PageHandler extends DefaultHandler {

    private final PageProcessor processor;
    private Page page;
    private StringBuilder stringBuilder;
    private boolean idSet = false;

    public PageHandler(PageProcessor processor) {
        this.processor = processor;
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
         //Unchanged from your implementation
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
         //Unchanged from your implementation
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
            //  Elide code not needing change

            } else if (qName.equals("page")){

                processor.process(page);
                page = null;

            }
        } else {
            page = null;
        }
    }

}

当然，您可以让您的界面处理多条记录的块，而不仅仅是一条记录，并让 PageHandler 将页面本地收集到一个较小的列表中，并定期发送列表进行处理并清除列表.

Of course, you can make your interface handle chunks of multiple records rather than just one and have the PageHandler collect pages locally in a smaller list and periodically send the list off for processing and clear the list.

或者(也许更好)您可以实现此处定义的 PageProcessor 接口，并在此处构建逻辑来缓冲数据并将其发送到块中以进一步处理.

Or (perhaps better) you could implement the PageProcessor interface as defined here and build in logic there that buffers the data and sends it on for further handling in chunks.

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