在Java中创建一个轻量级的XLSX读取器的原因是为了简化读取XLSX文件的过程。下面是解决方法的代码示例：

import javax.xml.namespace.QName;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.events.Attribute;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;
import java.nio.file.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class XLSXUtil {
    public static void main(String args[]) throws Exception {
        fetchDataFromExcel();
    }
    public static List> fetchDataFromExcel() throws Exception {
        List> result = new ArrayList<>();
        XMLEventReader reader = null;
        XMLEvent event = null;
        Attribute attribute = null;
        StartElement startElement = null;
        EndElement endElement = null;
        String characters = null;
        StringBuilder stringValue = new StringBuilder(); //for collecting the characters to complete values
        List sharedStrings = new ArrayList(); //list of shared strings
        Map numberFormats = new HashMap(); //map of number formats
        List cellNumberFormats = new ArrayList(); //list of cell number formats
        Path source = Paths.get("Sample.xlsx"); //path to the Excel file
        FileSystem fs = FileSystems.newFileSystem(source, null); //get filesystem of Excel file
        //get shared strings
        Path sharedStringsTable = fs.getPath("/xl/sharedStrings.xml");
        reader = XMLInputFactory.newInstance().createXMLEventReader(Files.newInputStream(sharedStringsTable));
        boolean siFound = false;
        while (reader.hasNext()) {
            event = (XMLEvent) reader.next();
            if (event.isStartElement()) {
                startElement = (StartElement) event;
                if (startElement.getName().getLocalPart().equalsIgnoreCase("si")) {
                    //start element of shared string item
                    siFound = true;
                    stringValue = new StringBuilder();
                }
            } else if (event.isCharacters() && siFound) {
                //chars of the shared string item
                characters = event.asCharacters().getData();
                stringValue.append(characters);
            } else if (event.isEndElement()) {
                endElement = (EndElement) event;
                if (endElement.getName().getLocalPart().equalsIgnoreCase("si")) {
                    //end element of shared string item
                    siFound = false;
                    sharedStrings.add(stringValue.toString());
                }
            }
        }
        reader.close();
        //get styles, number formats are essential for detecting date / time values
        Path styles = fs.getPath("/xl/styles.xml");
        reader = XMLInputFactory.newInstance().createXMLEventReader(Files.newInputStream(styles));
        boolean cellXfsFound = false;
        while (reader.hasNext()) {
            event = (XMLEvent) reader.next();
            if (event.isStartElement()) {
                startElement = (StartElement) event;
                if (startElement.getName().getLocalPart().equalsIgnoreCase("numFmt")) {
                    //start element of number format
                    attribute = startElement.getAttributeByName(new QName("numFmtId"));
                    String numFmtId = attribute.getValue();
                    attribute = startElement.getAttributeByName(new QName("formatCode"));
                    numberFormats.put(numFmtId, ((attribute != null) ? attribute.getValue() : "null"));
                } else if (startElement.getName().getLocalPart().equalsIgnoreCase("cellXfs")) {
                    //start element of cell format setting
                    cellXfsFound = true;
                } else if (startElement.getName().getLocalPart().equalsIgnoreCase("xf") && cellXfsFound) {
                    //start element of format setting in cell format setting
                    attribute = startElement.getAttributeByName(new QName("numFmtId"));
                    cellNumberFormats.add(((attribute != null) ? attribute.getValue() : "null"));
                }
            } else if (event.isEndElement()) {
                endElement = (EndElement) event;
                if (endElement.getName().getLocalPart().equalsIgnoreCase("cellXfs")) {
                    //end element of cell format setting
                    cellXfsFound = false;
                }
            }
        }
        reader.close();
        //get sheet data of first sheet
        Path sheet1 = fs.getPath("/xl/worksheets/sheet1.xml");
        reader = XMLInputFactory.newInstance().createXMLEventReader(Files.newInputStream(sheet1));
        boolean rowFound = false;
        boolean cellFound = false;
        boolean cellValueFound = false;
        boolean inlineStringFound = false;
        String cellStyle = null;
        String cellType = null;
        List row = null;
        while (reader.hasNext()) {
            event = (XMLEvent) reader.next();
            if (event.isStartElement()) {
                startElement = (StartElement) event;
                if (startElement.getName().getLocalPart().equalsIgnoreCase("row")) {
                    //start element of row
                    rowFound = true;
                    if (row != null) {
                        result.add(row);
                    }
                    row = new ArrayList<>();
                } else if (startElement.getName().getLocalPart().equalsIgnoreCase("c") && rowFound) {
                    //start element of cell in row
                    cellFound = true;
                    attribute = startElement.getAttributeByName(new QName("t"));
                    cellType = ((attribute != null) ? attribute.getValue() : null);
                    attribute = startElement.getAttributeByName(new QName("s"));
                    cellStyle = ((attribute != null) ? attribute.getValue() : null);
                } else if (startElement.getName().getLocalPart().equalsIgnoreCase("v") && cellFound) {
                    //start element of value in cell
                    cellValueFound = true;
                    stringValue = new StringBuilder();
                } else if (startElement.getName().getLocalPart().equalsIgnoreCase("is") && cellFound) {
                    //start element of inline string in cell
                    inlineStringFound = true;
                    stringValue = new StringBuilder();
                }
            } else if (event.isCharacters() && cellFound && (cellValueFound || inlineStringFound)) {
                //chars of the cell value or the inline string
                characters = event.asCharacters().getData();
                stringValue.append(characters);
            } else if (event.isEndElement()) {
                endElement = (EndElement) event;
                if (endElement.getName().getLocalPart().equalsIgnoreCase("row")) {
                    //end element of row
                    rowFound = false;
                } else if (endElement.getName().getLocalPart().equalsIgnoreCase("c")) {
                    //end element of cell
                    cellFound = false;
                } else if (endElement.getName().getLocalPart().equalsIgnoreCase("v")) {
                    //end element of value
                    cellValueFound = false;
                    String cellValue = stringValue.toString();
                    if ("s".equals(cellType)) {
                        cellValue = sharedStrings.get(Integer.valueOf(cellValue));
                    }
                    row.add(cellValue);
                } else if (endElement.getName().getLocalPart().equalsIgnoreCase("is")) {
                    //end element of inline string
                    inlineStringFound = false;
                    String cellValue = stringValue.toString();
                    row.add(cellValue);
                }
            }
        }
        reader.close();
        fs.close();
        return result;
    }
}

以上代码是一个轻量级的XLSX读取器的实现，可以读取简单的XLSX文件。它通过解析Excel文件中的XML数据来提取数据，并将其存储在一个二维列表中返回。这个读取器的主要思路是使用XML解析器来解析Excel文件中的各个部分，然后将所需的数据提取出来并存储在结果列表中。

该读取器主要包括以下步骤：

1. 通过Java的文件操作API获取Excel文件的路径和文件系统对象。

2. 使用XML解析器读取Excel文件中的共享字符串表，将所有共享字符串存储在一个列表中。

3. 读取Excel文件中的样式表，获取所有的数字格式，并存储在一个映射表中。

4. 读取Excel文件中的第一个工作表的数据，将每一行的数据存储在一个列表中，并将所有行的列表存储在结果列表中。

5. 关闭文件系统对象，返回结果列表。

这个轻量级的XLSX读取器可以方便地用于读取简单的XLSX文件，而不需要处理复杂的操作。通过使用XML解析器和Java的文件操作API，可以高效地从XLSX文件中提取所需的数据。