POI导入导出

POI（Poor Obfuscation Implementation）是Apache的一个开源项目，用来处理Microsoft Office文档。它可以导入和导出Excel、Word、PowerPoint等文件。

导入Excel文件：

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
 
public class ExcelReader {
    public static void main(String[] args) throws IOException {
        FileInputStream file = new FileInputStream(new File("path_to_your_excel_file.xlsx"));
 
        Workbook workbook = new XSSFWorkbook(file);
        Sheet sheet = workbook.getSheetAt(0);
 
        for (Row row : sheet) {
            for (Cell cell : row) {
                switch (cell.getCellType()) {
                    case STRING:
                        System.out.print(cell.getStringCellValue() + "\t");
                        break;
                    case NUMERIC:
                        System.out.print(cell.getNumericCellValue() + "\t");
                        break;
                    case BOOLEAN:
                        System.out.print(cell.getBooleanCellValue() + "\t");
                        break;
                    case FORMULA:
                        System.out.print(cell.getCellFormula() + "\t");
                        break;
                    default: break;
                }
            }
            System.out.println();
        }
        workbook.close();
        file.close();
    }
}

导出Excel文件：

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
 
import java.io.FileOutputStream;
import java.io.IOException;
 
public class ExcelWriter {
    public static void main(String[] args) throws IOException {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sample Sheet");
 
        Row row = sheet.createRow(0);
        Cell cell = row.createCell(0);
        cell.setCellValue("Hello, World!");
 
        FileOutputStream fileOut = new FileOutputStream("path_to_your_excel_file.xlsx");
        workbook.write(fileOut);
        fileOut.close();
        workbook.close();
    }
}

注意：在实际应用中，你需要处理文件路径、错误处理、内存管理等问题。上述代码仅展示了POI的基本使用方法。