Detailed explanation of the basic use of Apache POI

<dependency>
  <groupId>org.apache.poi</groupId>
  <artifactId>poi</artifactId>
  <version>3.14</version>
</dependency>
<dependency>
  <groupId>org.apache.poi</groupId>
  <artifactId>poi-ooxml</artifactId>
  <version>3.14</version>
</dependency>

package com.yy.test;

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;
import org.junit.Test;

import java.io.File;
import java.io.FileInputStream;

/**
 * @author Marston
 * @date 2021/10/29
 */
public class POITest {
    @Test
    public void test() throws Exception {
        // Pass in an input stream, load the specified file, and create an Excel object (workbook)
        XSSFWorkbook excel = new XSSFWorkbook(new FileInputStream(new File("E:\\testNomal\\poi.xlsx")));
        //Read the first Sheet tab in the Excel file XSSFSheet sheet = excel.getSheetAt(0);
        //There are many rows in a sheet page. Traverse the sheet tab page and get each row of data for (Row row : sheet) {
            //Traverse the rows and get each cell object for (Cell cell : row) {
                //cell represents the cell object System.out.println(cell.getStringCellValue()); //getStringCellValue The second column is a numeric value and cannot be converted to a String type, so an error is reported //Just change the content of the second column in the Excel table to a string type. }
        }
        //Close the Excel fileexcel.close();
    }
}

package com.yy.test;

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

import java.io.File;
import java.io.FileInputStream;

/**
 * @author Marston
 * @date 2021/10/29
 */
public class POITest {
    @Test
    public void test2() throws Exception {
        // Pass in an input stream, load the specified file, and create an Excel object (workbook)
        XSSFWorkbook excel = new XSSFWorkbook(new FileInputStream(new File("E:\\testNomal\\poi.xlsx")));
        //Read the first Sheet tab in the Excel file XSSFSheet sheet = excel.getSheetAt(0);
        //Get the row number of the last row of the current worksheet. The row number starts from 0 int lastRowNum = sheet.getLastRowNum();
        System.out.println("lastRowNum: "+lastRowNum);
        for(int i=0;i<=lastRowNum;i++){
            //Get each row according to the row number XSSFRow row = sheet.getRow(i);
            //Get the last cell index of the current row short lastCellNum = row.getLastCellNum();
            System.out.println("lastCellNum: "+lastCellNum);
            for(short j=0;j<lastCellNum;j++){
                //Get cell content based on cell index String value = row.getCell(j).getStringCellValue();
                System.out.println(value);
            }
        }
        //Close the Excel fileexcel.close();
    }
}

//Use POI to write data to the Excel file, and save the created Excel file to the local disk through the output stream //@Test
    public void test3() throws Exception{
        //Create an Excel file (workbook) in memory
        XSSFWorkbook excel = new XSSFWorkbook();
        //Create a worksheet object named: POI write test XSSFSheet sheet = excel.createSheet("POI write test");
        //Create row objects in the worksheet and create XSSFRow in the first row title = sheet.createRow(0);
        //Create a cell object in the row title.createCell(0).setCellValue("Name"); //Content of the first column title.createCell(1).setCellValue("Address");
        title.createCell(2).setCellValue("age");

		//Create XSSFRow in the second row dataRow = sheet.createRow(1);
        dataRow.createCell(0).setCellValue("Xiao Ming");
        dataRow.createCell(1).setCellValue("Beijing");
        dataRow.createCell(2).setCellValue("20");

        //Create an output stream and write the Excel file in memory to disk through the output stream FileOutputStream out = new FileOutputStream(new File("e:\\hello.xlsx"));
        excel.write(out);//write out.flush();//refresh excel.close();
    }