一个Excel文件对应于一个workbook(HSSFWorkbook)，
一个workbook可以有多个sheet（HSSFSheet）组成，
一个sheet是由多个row（HSSFRow）组成，
一个row是由多个cell（HSSFCell）组成

<dependency>  
    <groupId>org.apache.poi</groupId>  
    <artifactId>poi</artifactId>  
    <version>3.8</version>  
</dependency>

public static void createExcel() throws IOException{ 
   
	// 获取桌面路径
	FileSystemView fsv = FileSystemView.getFileSystemView();
	String desktop = fsv.getHomeDirectory().getPath();
	String filePath = desktop + "/template.xls";
	
	File file = new File(filePath);
	OutputStream outputStream = new FileOutputStream(file);
	HSSFWorkbook workbook = new HSSFWorkbook();
	HSSFSheet sheet = workbook.createSheet("Sheet1");
	HSSFRow row = sheet.createRow(0);
	row.createCell(0).setCellValue("id");
	row.createCell(1).setCellValue("订单号");
	row.createCell(2).setCellValue("下单时间");
	row.createCell(3).setCellValue("个数");
	row.createCell(4).setCellValue("单价");
	row.createCell(5).setCellValue("订单金额");
	row.setHeightInPoints(30); // 设置行的高度
	
	HSSFRow row1 = sheet.createRow(1);
	row1.createCell(0).setCellValue("1");
	row1.createCell(1).setCellValue("NO00001");
	
	// 日期格式化
	HSSFCellStyle cellStyle2 = workbook.createCellStyle();
	HSSFCreationHelper creationHelper = workbook.getCreationHelper();
	cellStyle2.setDataFormat(creationHelper.createDataFormat().getFormat("yyyy-MM-dd HH:mm:ss"));
	sheet.setColumnWidth(2, 20 * 256); // 设置列的宽度
	
	HSSFCell cell2 = row1.createCell(2);
	cell2.setCellStyle(cellStyle2);
	cell2.setCellValue(new Date());
	
	row1.createCell(3).setCellValue(2);
	
	
	// 保留两位小数
	HSSFCellStyle cellStyle3 = workbook.createCellStyle();
	cellStyle3.setDataFormat(HSSFDataFormat.getBuiltinFormat("0.00"));
	HSSFCell cell4 = row1.createCell(4);
	cell4.setCellStyle(cellStyle3);
	cell4.setCellValue(29.5);
	
	
	// 货币格式化
	HSSFCellStyle cellStyle4 = workbook.createCellStyle();
	HSSFFont font = workbook.createFont();
	font.setFontName("华文行楷");
	font.setFontHeightInPoints((short)15);
	font.setColor(HSSFColor.RED.index);
	cellStyle4.setFont(font);
	
	HSSFCell cell5 = row1.createCell(5);
	cell5.setCellFormula("D2*E2");  // 设置计算公式
	
	// 获取计算公式的值
	HSSFFormulaEvaluator e = new HSSFFormulaEvaluator(workbook);
	cell5 = e.evaluateInCell(cell5);
	System.out.println(cell5.getNumericCellValue());

	
	workbook.setActiveSheet(0);
	workbook.write(outputStream);
	outputStream.close();
}

public static void readExcel() throws IOException{ 
   
	FileSystemView fsv = FileSystemView.getFileSystemView();
	String desktop = fsv.getHomeDirectory().getPath();
	String filePath = desktop + "/template.xls";
	
	FileInputStream fileInputStream = new FileInputStream(filePath);
	BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);
	POIFSFileSystem fileSystem = new POIFSFileSystem(bufferedInputStream);
	HSSFWorkbook workbook = new HSSFWorkbook(fileSystem);
	HSSFSheet sheet = workbook.getSheet("Sheet1");
	
	int lastRowIndex = sheet.getLastRowNum();
	System.out.println(lastRowIndex);
	for (int i = 0; i <= lastRowIndex; i++) { 
   
		HSSFRow row = sheet.getRow(i);
		if (row == null) { 
    break; }
		
		short lastCellNum = row.getLastCellNum();
		for (int j = 0; j < lastCellNum; j++) { 
   
			String cellValue = row.getCell(j).getStringCellValue();
			System.out.println(cellValue);
		}
	}
	
	
	bufferedInputStream.close();
}

@SuppressWarnings("resource")
@RequestMapping("/export")    
public void exportExcel(HttpServletResponse response, HttpSession session, String name) throws Exception { 
     
	
	String[] tableHeaders = { 
   "id", "姓名", "年龄"}; 
	
	HSSFWorkbook workbook = new HSSFWorkbook();
	HSSFSheet sheet = workbook.createSheet("Sheet1");
	HSSFCellStyle cellStyle = workbook.createCellStyle();    
	cellStyle.setAlignment(HorizontalAlignment.CENTER);  
	cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);
	
	Font font = workbook.createFont();  
	font.setColor(HSSFColor.RED.index);  
	font.setBold(true);
	cellStyle.setFont(font);
	
	// 将第一行的三个单元格给合并
	sheet.addMergedRegion(new CellRangeAddress(0, 0, 0, 2));
	HSSFRow row = sheet.createRow(0);
	HSSFCell beginCell = row.createCell(0);
	beginCell.setCellValue("通讯录");	
	beginCell.setCellStyle(cellStyle);
	
	row = sheet.createRow(1);
	// 创建表头
	for (int i = 0; i < tableHeaders.length; i++) { 
   
		HSSFCell cell = row.createCell(i);
		cell.setCellValue(tableHeaders[i]);
		cell.setCellStyle(cellStyle);    
	}
	
	List<User> users = new ArrayList<>();
	users.add(new User(1L, "张三", 20));
	users.add(new User(2L, "李四", 21));
	users.add(new User(3L, "王五", 22));
	
	for (int i = 0; i < users.size(); i++) { 
   
		row = sheet.createRow(i + 2);
		
		User user = users.get(i);
		row.createCell(0).setCellValue(user.getId());    
		row.createCell(1).setCellValue(user.getName());    
		row.createCell(2).setCellValue(user.getAge());    
	}
	
	OutputStream outputStream = response.getOutputStream(); 
	response.reset(); 
	response.setContentType("application/vnd.ms-excel");    
	response.setHeader("Content-disposition", "attachment;filename=template.xls");      

	workbook.write(outputStream);
	outputStream.flush();    
	outputStream.close();
}

<dependency>
	<groupId>commons-fileupload</groupId>
	<artifactId>commons-fileupload</artifactId>
	<version>1.3</version>
</dependency>

<bean name="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">  
	<property name="defaultEncoding" value="UTF-8" />
</bean>

<a href="/Spring-Mybatis-Druid/user/export">导出</a> <br/>

<form action="/Spring-Mybatis-Druid/user/import" enctype="multipart/form-data" method="post">
	<input type="file" name="file"/> 
	<input type="submit" value="导入Excel">
</form>

@SuppressWarnings("resource")
@RequestMapping("/import")
public void importExcel(@RequestParam("file") MultipartFile file) throws Exception{ 
   
	InputStream inputStream = file.getInputStream();
	BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
	POIFSFileSystem fileSystem = new POIFSFileSystem(bufferedInputStream);
	HSSFWorkbook workbook = new HSSFWorkbook(fileSystem);
	//HSSFWorkbook workbook = new HSSFWorkbook(file.getInputStream());
	HSSFSheet sheet = workbook.getSheetAt(0);
	
	int lastRowNum = sheet.getLastRowNum();
	for (int i = 2; i <= lastRowNum; i++) { 
   
		HSSFRow row = sheet.getRow(i);
		int id = (int) row.getCell(0).getNumericCellValue();
		String name = row.getCell(1).getStringCellValue();
		int age = (int) row.getCell(2).getNumericCellValue();
		
		System.out.println(id + "-" + name + "-" + age);
	}
}