将 XML 拆分为指定大小的较小 XML 文件

Question

我对 XML 很陌生，坏消息是我有以下结构的 XML：

<record>
   <record_id>200</record_id>
   <record_rows>
        <record_row>some text</record_row>
        .................................
   </record_rows>
</record>

每条记录的记录行数不同，因此，每条记录的大小也有很大不同。我的任务是将文件（超过 1GB）拆分为指定大小的单独 xml 文件。哪个解析器是最好的？另外，我想我应该采用一些记录选择策略来接近目标大小（考虑到输入文件大小和下一个记录大小的不可预测性，我当时无法想象）

朋友们，唯一的希望寄托在你们身上。你会如何处理这个问题？

Answer 1

假设您的记录行不大于单个文件的所需大小，您可以使用 SAX 解析器按顺序读取文件并计算读取的字符数，将目前读取的数据存储在缓冲区中。当字符数达到接近大小限制的值时，它将创建一个仅包含到目前为止读取的记录的新文件，重置缓冲区和字符数，并继续读取另一个集合，直到再次达到限制，并且很快。最后，您将拥有一组大小大致相同的文件（除了最后一个可能更小）并且包含相同的数据。

要使用 SAX 解析器，您需要一个包含以下代码的可执行文件：

import java.io.*;
import javax.xml.parsers.*;
import org.xml.sax.*;

public class SAXReader {

    public static final String PATH = "src/main/resources";

    public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException {
        SAXParserFactory spf = SAXParserFactory.newInstance();
        SAXParser sp = spf.newSAXParser();
        XMLReader reader = sp.getXMLReader();
        reader.setContentHandler(new DataSaxHandler()); // need to implement this file
        reader.parse(new InputSource(new FileInputStream(new File(PATH, "data.xml"))));
    }
}

您的 XML 文件存储在 src/main/resources/data.xml（相对于您运行应用程序的位置）。你可能想改变它。

如果要拆分的文件是格式良好的 XML，它们还应该有一个根元素，并且可能保留诸如 record_id 之类的信息，这样您就可以知道它们来自哪个记录。我添加了一个属性part，其中包含一个对文件片段进行排序的序列号。生成的文件将如下所示：

data_part_1.xml

<record part='1'><record_id>200</record_id><record_rows><record_row>...</record_row><record_row>...</record_row> ... <record_row>...</record_row></record_rows></record>

data_part_2.xml

<record part='2'><record_id>200</record_id><record_rows><record_row>...</record_row><record_row>...</record_row> ... <record_row>...</record_row></record_rows></record>

...

data_part_n.xml

<record part='n'><record_id>200</record_id><record_rows><record_row>...</record_row><record_row>...</record_row><record_row>...</record_row><record_row>...</record_row></record_rows></record>

其中“n”是创建的文件数。

实现此结果的 SAX ContentHandler 实现如下所示。您可能想要更改 DIRECTORY 和 MAX_SIZE 常量：

import java.io.*;
import org.xml.sax.*;
import org.xml.sax.helpers.DefaultHandler;

class DataSaxHandler extends DefaultHandler {

    // Change this to the directory where the files will be stored
    public static final String DIRECTORY = "target/results"; 

    // Change this to the approximate size of the resulting files (in characters(
    public static final long MAX_SIZE = 1024;


    public static final long TAG_CHAR_SIZE = 5; //"<></>"

    // counts number of files created
    private int fileCount = 0;

    // counts characters to decide where to split file
    private long charCount = 0;
    // data line buffer (is reset when the file is split)
    private StringBuilder recordRowDataLines = new StringBuilder();

    // temporary variables used for the parser events
    private String currentElement = null;
    private String currentRecordId = null;
    private String currentRecordRowData = null;

    @Override
    public void startDocument() throws SAXException {
        File dir = new File(DIRECTORY);
        if (!dir.exists()) {
            dir.mkdir();
        }
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
        currentElement = qName;
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if (qName.equals("record_rows")) { // no more records - save last file here!
            try {
                saveFragment();
            } catch (IOException ex) {
                throw new SAXException(ex);
            }
        }
        if (qName.equals("record_row")) { // one record finished - save in buffer & calculate size so far
            charCount += tagSize("record_row");
            recordRowDataLines.append("<record_row>")
                              .append(currentRecordRowData)
                              .append("</record_row>");
            if (charCount >= MAX_SIZE) { // if max size was reached, save what was read so far in a new file
                try {
                    saveFragment();
                } catch (IOException ex) {
                    throw new SAXException(ex);
                }
            }
        }
        currentElement = null;
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        System.out.println(new String(ch, start, length));
        if (currentElement == null) {
            return;
        }
        if (currentElement.equals("record_id")) {
            currentRecordId = new String(ch, start, length); 
        }
        if (currentElement.equals("record_row")) {
            currentRecordRowData = new String(ch, start, length);
            charCount += currentRecordRowData.length(); // storing size so far
        }
    }

    public long tagSize(String tagName) {
        return TAG_CHAR_SIZE + tagName.length() * 2; // size of text + tags
    }

    /**
     * Saves a new file containing approximately MAX_SIZE in chars 
     */
    public void saveFragment() throws IOException {
        ++fileCount;
        StringBuilder fileContent = new StringBuilder();
        fileContent.append("<record part='")
                   .append(fileCount)
                   .append("'><record_id>")
                   .append(currentRecordId)
                   .append("</record_id>")
                   .append("<record_rows>")
                   .append(recordRowDataLines)
                   .append("</record_rows></record>");
        File fragment = new File(DIRECTORY, "data_part_" + fileCount + ".xml");
        FileWriter out = new FileWriter(fragment);
        out.write(fileContent.toString());
        out.flush();
        out.close();

        // reset fragment data - record buffer and char count
        recordRowDataLines = new StringBuilder();
        charCount = 0;
    }

}