Import and export using poi

Official website ：https://poi.apache.org/

1、ApachePOI Introduce

ApachePOI Yes, it is Java Write free open source cross platform JavaAPI,ApachePOI Provide API to Java Program pair MicrosoftOffice Format file reading and writing functions , One of the most used is the use of POI operation Excel file .

2、 Use ApachePOI Used jar Packet dependency

<!-- poi My bag  3.15 After the version, the method of getting cell type has been adjusted  -->
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>5.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.2.1</version>
        </dependency>

3、POI The use of API Explain

3.1、 structure

HSSF－ Provide reading and writing Microsoft Excel XLS The function of format file
XSSF－ Provide reading and writing Microsoft ExcelOOXML XLSX The function of format file
HWPF－ Provide reading and writing Microsoft Word DOC The function of format file
HSLF－ Provide reading and writing MicrosoftPowerPoint The function of format file
HDGF－ Offer to read MicrosoftVisio The function of format file
HPBF－ Offer to read MicrosoftPublisher The function of format file
HSMF－ Offer to read MicrosoftOutlook The function of format file

3.2、 object
3.2.1、.xls and .xlsx The difference between ：
excel There are two suffixes , The early xls And later xlsx,

• HSSFWorkbook: Is the operation Excel2003 before （ Include 2003） Version of , The extension is .xls, The maximum number of rows exported is 65535 That's ok , beyond 65536 After the entry, the system will report an error
• XSSFWorkbook: Is the operation Excel2007 Version of , The extension is .xlsx, Export at most 1048576 That's ok ,

SXSSFWorkbook from POI 3.8 Version start , Provides a XSSF Of low memory usage SXSSF The way . For large excel File creation , A key issue is , Make sure there is no memory overflow . Actually , Even if it generates very small excel（ How about Mb）, It uses far more memory than excel The document is actually size Of . If the cell has various formats （ such as , In bold , The background is marked red or something ）, Then it takes up more memory . For large excel Created without memory overflow , Only SXSSFWorkbook 了 . Its principle is very simple , Swap hard disk space for memory （ It's like hash map Trade space for time ）.

3.2.2、xls and xlsx Medium Content-type difference

• 2003 Excel edition .xls Of Content-type by application/vnd.ms-excel
• 2010 Excel edition .xlsx Of Content-type by application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

Reference resources ：https://blog.csdn.net/xiaoyu19910321/article/details/79279364

3.2.3、xls Common components ：

HSSFWorkbook : excel Document object for
HSSFSheet : excel Form for
HSSFRow : excel The line of
HSSFCell : excel The grid unit of
HSSFFont : excel typeface
HSSFDataFormat: Date format
HSSFHeader : sheet head
HSSFFooter : sheet tail （ You can only see the effect when you print it ）

3.2.4 style

HSSFCellStyle : cell style

3.2.5 Auxiliary operations include ：

HSSFDateUtil : date
HSSFPrintSetup : Print
HSSFErrorConstants : Error message table

3.2.6 xlsx Common components ：

XSSFWorkbook : excel Document object for
XSSFSheet: excel Form for
XSSFRow: excel The line of
XSSFCell: excel The grid unit of
XSSFFont: excel typeface
XSSFDataFormat : Date format

3.2.7 Description of the common field type of the two components
In fact, the two components are aimed at excel Two formats of , Most of the operations are the same .

3.2.8 Operation steps
With HSSF For example ,XSSF Same operation .

First , Understand a Excel The organization form of the document , One Excel The file corresponds to a workbook(HSSFWorkbook), One workbook There can be multiple sheet（HSSFSheet） form , One sheet It's made up of many row（HSSFRow） form , One row It's made up of many cell（HSSFCell） form .

1、 use HSSFWorkbook Open or create “Excel File object ”
2、 use HSSFWorkbook Object returns or creates Sheet object
3、 use Sheet Object returns the row object , Get by row object Cell object
4、 Yes Cell Object reading and writing .

4、 Import / Upload code display

package com.example.demo.utils;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.util.IOUtils;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.multipart.MultipartFile;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

import static org.apache.poi.ss.usermodel.CellType.*;
import static org.apache.poi.ss.usermodel.CellType.NUMERIC;

/** * @author lvxu * @create 2022-07-10 13:30 */
public class PoiUtil {
    
    private final static Logger logger = LoggerFactory.getLogger(PoiUtil.class);

    private final static String xls = ".xls";
    private final static String xlsx = ".xlsx";

    /** *  Read in excel file , After parsing, return  * * @param file * @throws IOException */
    public static List<String[]> readExcel(MultipartFile file) throws IOException {
    
        // Check the documents 
        checkFile(file);
        // get Workbook Workbook object 
        Workbook workbook = getWorkBook(file);
        // Create return object , Take the values in each row as an array , All rows are returned as a collection 
        List<String[]> list = new ArrayList<String[]>();
        if (workbook != null) {
    
            //  Go through each one workbook How many workbook objects sheet  use workbook.getNumberOfSheets()  This is the way to get sheet Number 
            for (int sheetNum = 0; sheetNum < workbook.getNumberOfSheets(); sheetNum++) {
    
                // Get the current  sheet  Worksheet object 
                Sheet sheet = workbook.getSheetAt(sheetNum);
                if (sheet == null) {
    
                    continue;
                }
                // Get the current sheet The beginning of the line 
                int firstRowNum = sheet.getFirstRowNum();
                // Get the current sheet End line of 
                int lastRowNum = sheet.getLastRowNum();
                // Loop all lines except the first one 
                for (int rowNum = firstRowNum + 1; rowNum <= lastRowNum; rowNum++) {
    
                    // Get the current line 
                    Row row = sheet.getRow(rowNum);
                    if (row == null) {
    
                        continue;
                    }
                    // Get the start column of the current row 
                    int firstCellNum = row.getFirstCellNum();
                    // Gets the number of columns in the current row 
                    int lastCellNum = row.getPhysicalNumberOfCells();
                    String[] cells = new String[row.getPhysicalNumberOfCells()];
                    // Loop current line   Traverse from the first column of the current row   To the last column 
                    for (int cellNum = firstCellNum; cellNum < lastCellNum; cellNum++) {
    
                        Cell cell = row.getCell(cellNum);
                        cells[cellNum] = getCellValue(cell);
                    }
                    list.add(cells);
                }
            }
            workbook.close();
        }
        return list;
    }

    public static void checkFile(MultipartFile file) throws IOException {
    
        // Judge whether the file exists 
        if (null == file) {
    
            logger.error(" file does not exist ！");
            throw new FileNotFoundException(" file does not exist ！");
        }
        // Get the filename 
        String fileName = file.getOriginalFilename();
        // Determine if the document is excel file 
        if (!fileName.endsWith(xls) && !fileName.endsWith(xlsx)) {
    
            logger.error(fileName + " No excel file ");
            throw new IOException(fileName + " No excel file ");
        }

        // File format verification 
        if (!fileName.matches("^.+\\.(?i)(xls)$") && !fileName.matches("^.+\\.(?i)(xLsx)")) {
    
            throw new IOException(fileName + " No excel file ");
        }
    }

    public static Workbook getWorkBook(MultipartFile file) {
    
        // Get the filename 
        String fileName = file.getOriginalFilename();
        // establish Workbook Workbook object , Represents the whole excel
        Workbook workbook = null;
        try {
    
            // obtain excel Of documents io flow 
            InputStream is = file.getInputStream();
            // Depending on the file suffix (xls and xlsx) Get different Workbook Implementation class object 
            if (fileName.endsWith(xls)) {
    
                //2003
                workbook = new HSSFWorkbook(is);
            } else if (fileName.endsWith(xlsx)) {
    
                //2007
                workbook = new XSSFWorkbook(is);
            }
        } catch (IOException e) {
    
            logger.info(e.getMessage());
        }
        return workbook;
    }

    public static String getCellValue(Cell cell) {
    
        String cellValue = "";
        if (cell == null) {
    
            return cellValue;
        }
        // Think of numbers as String To read , Avoid 1 Read into 1.0 The situation of 
        if (cell.getCellType() == NUMERIC) {
    
            cell.setCellType(STRING);
        }
        // Determine the type of data 
        switch (cell.getCellType()) {
    
            case NUMERIC: // Numbers 
                cellValue = String.valueOf(cell.getNumericCellValue());
                break;
            case STRING: // character string 
                cellValue = String.valueOf(cell.getStringCellValue());
                break;
            case BOOLEAN: //Boolean
                cellValue = String.valueOf(cell.getBooleanCellValue());
                break;
            case FORMULA: // The formula 
                cellValue = String.valueOf(cell.getCellFormula());
                break;
            case BLANK: // Null value 
                cellValue = "";
                break;
            case ERROR: // fault 
                cellValue = " Illegal characters ";
                break;
            default:
                cellValue = " Unknown type ";
                break;
        }
        return cellValue;
    }
}

Reference link ：https://blog.csdn.net/xingxingmingyue/article/details/111468329
https://blog.csdn.net/weixin_43952697/article/details/107249935

https://blog.csdn.net/Smallextremely/article/details/121035673