Question

我有两个Java程序：一个用于创建数据并将数据写入XLSX文件，另一个用于读取同一文件中的数据。

在我的第一个程序中，我使用下面的语句将数据写入XLSX文件。

FileOutputStream prelimOut = new FileOutputStream(new File("D:\\News\\Prelim.xlsx"));
XSSFWorkbook out = new XSSFWorkbook();
XSSFSheet spreadSheet = out.createSheet("ResultSheet");

在我的驱动器上，我按照预期创建了文件。

当我尝试使用此代码从其他程序读取同一文件时

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Iterator;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class GetCellCount {
    public static void main(String[] args) throws IOException {
        FileInputStream input_document = new FileInputStream(new File("D:\\News\\Prelim.xlsx"));
        XSSFWorkbook my_xlsx_workbook = new XSSFWorkbook(input_document);
        XSSFSheet my_worksheet = my_xlsx_workbook.getSheetAt(0);
        Iterator<Row> rowIterator = my_worksheet.iterator();
        while (rowIterator.hasNext()) {
            Row row = rowIterator.next();
            Iterator<Cell> cellIterator = row.cellIterator();
            while (cellIterator.hasNext()) {
                Cell cell = cellIterator.next();
                switch (cell.getCellType()) {
                case Cell.CELL_TYPE_NUMERIC:
                    System.out.print(cell.getNumericCellValue() + "\t\t");
                    break;
                case Cell.CELL_TYPE_STRING:
                    System.out.print(cell.getStringCellValue() + "\t\t");
                    break;
                }
            }
            System.out.println("");
        }
        my_xlsx_workbook.close();
        input_document.close();
    }
}

它抛出以下错误

Exception in thread "main" org.apache.poi.POIXMLException: org.apache.poi.openxml4j.exceptions.InvalidFormatException: Package should contain a content type part [M1.13]
    at org.apache.poi.util.PackageHelper.open(PackageHelper.java:39)
    at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:258)
    at GetCellCount.main(GetCellCount.java:14)
Caused by: org.apache.poi.openxml4j.exceptions.InvalidFormatException: Package should contain a content type part [M1.13]
    at org.apache.poi.openxml4j.opc.ZipPackage.getPartsImpl(ZipPackage.java:203)
    at org.apache.poi.openxml4j.opc.OPCPackage.getParts(OPCPackage.java:673)
    at org.apache.poi.openxml4j.opc.OPCPackage.open(OPCPackage.java:274)
    at org.apache.poi.util.PackageHelper.open(PackageHelper.java:37)
    ... 2 more

更改路径并访问另一个XLSX文件（直接在Excel中创建）时，数据会正确显示。

此外，当我通过右键单击它们来检查这两个Excel文件的属性时，我看到＆＃34;文件类型＆＃34;为MS Office Excel OpenXML (.xlsx)，两个文件都相同。

Answer 1

以下代码演示了如何使用数据创建一个新的XLSX文件，将其写入磁盘以及从文件中读取数据。它是使用Java 9和Apache POI 3.17构建的。

该示例使用一个简单的Person类，其中包含一个String，一个LocalDate和一个Int来生成测试数据。

这是在我们将测试数据写入其中之后，使用LibreOffice查看的已创建的XLSX文件：

LibreOffice with test data

写入文件后，我们读回其内容并创建Person对象：

Could not parse row 0 to person
Person from file: Khaled, born 1988-03-26, pets: 1
Person from file: Hans, born 1998-09-20, pets: 2
Person from file: Alena, born 1977-01-12, pets: 0

由于我们无法将标题行Name Date of Birth Nr of Pets转换为Person对象，因此出现第一行警告。

代码如下：

/**
* Writes person data to an XLSX file and reads it back out.
* <p>
* Created by Matthias Braun on 2018-07-10.
*/
public class ReadWriteTests {

    public static void main(String... args) {
        List<Person> people = List.of(
                new Person("Khaled", LocalDate.of(1988, 3, 26), 1),
                new Person("Hans", LocalDate.of(1998, 9, 20), 2),
                new Person("Alena", LocalDate.of(1977, 1, 12), 0)
        );
        String xlsxFileName = System.getenv("HOME") + "/people.xlsx";
        writeToXlsxFile(people, xlsxFileName);

        List<Person> peopleFromFile = readFromXlsxFile(xlsxFileName);

        peopleFromFile.forEach(person ->
                System.out.println("Person from file: " + person));
    }

    private static List<Person> readFromXlsxFile(String xlsxFileName) {
        return getRows(new File(xlsxFileName)).stream()
                .map(row -> rowToPerson(row))
                // Remove empty Optionals
                .flatMap(Optional::stream)
                .collect(Collectors.toList());
    }

    private static Optional<Person> rowToPerson(Row row) {
        Optional<Person> personMaybe;
        try {
            String name = row.getCell(0).getStringCellValue();

            Date date = row.getCell(1).getDateCellValue();
            // Convert from Date to LocalDate
            LocalDate dateOfBirth = LocalDate.ofInstant(
                    date.toInstant(), ZoneId.systemDefault());

            int nrOfPets = (int) row.getCell(2).getNumericCellValue();

            personMaybe = Optional.of(new Person(name, dateOfBirth, nrOfPets));
        } catch (IllegalStateException ex) {
            System.err.println("Could not parse row " + row.getRowNum()
                    + " to person");
            personMaybe = Optional.empty();
        }
        return personMaybe;
    }

    private static List<Row> getRows(final File xlsx) {

        final List<Row> rows = new ArrayList<>();

        try (XSSFWorkbook workbook = new XSSFWorkbook(xlsx)) {
            // Get each row from each sheet
            workbook.forEach(sheet -> sheet.forEach(rows::add));

            // If Apache POI tries to open a non-existent file it will throw
            // an InvalidOperationException, if it's an unrecognized format
            // it will throw a NotOfficeXmlFileException.
            // We catch them all to be safe.
        } catch (Exception e) {
            System.err.println("Could not get rows from "
                    + xlsx.getAbsolutePath());
            e.printStackTrace();
        }
        return rows;
    }

    private static void writeToXlsxFile(List<Person> people, String fileName) {

        try (OutputStream fileStream = new FileOutputStream(fileName)) {
            Workbook workbook = new XSSFWorkbook();

            Sheet sheet = workbook.createSheet("Test People Sheet");

            // Create a header row describing what the columns mean
            CellStyle boldStyle = workbook.createCellStyle();
            Font font = workbook.createFont();
            font.setBold(true);
            boldStyle.setFont(font);

            Row headerRow = sheet.createRow(0);
            addStringCells(headerRow,
                    List.of("Name", "Date of Birth", "Nr of Pets"),
                    boldStyle);

            // Define how a cell containing a date is displayed
            CellStyle dateCellStyle = workbook.createCellStyle();
            CreationHelper createHelper = workbook.getCreationHelper();
            dateCellStyle.setDataFormat(createHelper.createDataFormat()
                    .getFormat("yyyy/m/d"));

            // Add the person data as rows
            for (int i = 0; i < people.size(); i++) {
                // Add one due to the header row
                Row row = sheet.createRow(i + 1);
                Person person = people.get(i);
                addCells(person, row, dateCellStyle);
            }

            workbook.write(fileStream);
            workbook.close();

        } catch (IOException e) {
            System.err.println("Could not create XLSX file at " + fileName);
            e.printStackTrace();
        }
    }

    private static void addCells(Person person, Row row,
                                CellStyle dateCellStyle) {

        Cell classCell = row.createCell(0, CellType.STRING);
        classCell.setCellValue(person.getName());

        Cell dateOfBirthCell = row.createCell(1, CellType.NUMERIC);
        // Convert LocalDate to a legacy Date object
        Date dateOfBirth = Date.from(person.getDateOfBirth()
                .atStartOfDay(ZoneId.systemDefault()).toInstant());
        dateOfBirthCell.setCellValue(dateOfBirth);
        dateOfBirthCell.setCellStyle(dateCellStyle);

        Cell petCell = row.createCell(2, CellType.NUMERIC);
        petCell.setCellValue(person.getNrOfPets());
    }

    // Adds strings as styled cells to a row
    private static void addStringCells(Row row, List<String> strings,
                                      CellStyle style) {
        for (int i = 0; i < strings.size(); i++) {
            Cell cell = row.createCell(i, CellType.STRING);
            cell.setCellValue(strings.get(i));
            cell.setCellStyle(style);
        }
    }

    static class Person {
        private final String name;
        private final LocalDate dateOfBirth;
        private final int nrOfPets;

        Person(String name, LocalDate dateOfBirth, int nrOfPets) {
            this.name = name;
            this.dateOfBirth = dateOfBirth;
            this.nrOfPets = nrOfPets;
        }

        String getName() {
            return name;
        }

        LocalDate getDateOfBirth() {
            return dateOfBirth;
        }

        int getNrOfPets() {
            return nrOfPets;
        }

        @Override
        public String toString() {
            return name + ", born " + dateOfBirth + ", pets: " + nrOfPets;
        }
    }
}

包含依赖性的build.gradle，用./gradle run启动应用程序：

apply plugin: "application"
apply plugin: "java"

mainClassName = "com.bullbytes.ReadWriteTests"

sourceCompatibility = 9

repositories {
    mavenCentral()
}

dependencies {
    // Read and write Microsoft Office files: https://poi.apache.org
    // https://mvnrepository.com/artifact/org.apache.poi/poi
    compile "org.apache.poi:poi:3.17"
    compile "org.apache.poi:poi-ooxml:3.17"
}

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