Apache POI是Apache软件基金会的开放源码函式库，POI提供API给Java程式对Microsoft Office格式档案读和写的功能。

接口：

HSSF － Microsoft Excel

XSSF － Microsoft Excel OOXML(07以上版本)

HWPF － Microsoft Word

HSLF － Microsoft PowerPoint

HDGF － Microsoft Visio

EXCEL 结构：

HSSFWorkbook excell文档对象

HSSFSheet excell的表单

HSSFRow excell的行

HSSFCell excell的格子单元

HSSFFont excell字体

HSSFName 名称

HSSFDataFormat 日期格式

读Excel

读取Excel文件时，首先生成一个POIFSFileSystem对象，由POIFSFileSystem对象构造一个HSSFWorkbook，该HSSFWorkbook对象就代表了Excel文档

代码：

FileInputStream is = new FileInputStream("test.xls");

POIFSFileSystem fs = new POIFSFileSystem(is);

HSSFWorkbook wb = new HSSFWorkbook(fs);

HSSFSheet sheet = wb.getSheetAt(0);

HSSFRow row = sheet.getRow(0);

HSSFCell cell = row.getCell((short) 0);

String msg = cell.getStringCellValue();

写Excel

FileInputStream is = new FileInputStream("test.xls");

POIFSFileSystem fs = new POIFSFileSystem(is);

HSSFWorkbook wb = new HSSFWorkbook(fs);

HSSFSheet sheet = wb.getSheetAt(0);

HSSFRow row = sheet.getRow(0);

HSSFCell cell = row.getCell((short)0);

cell.setCellValue("a test");

FileOutputStream os = new FileOutputStream("test.xls ");

wb.write(os);

os.close();

设置行高、列宽

sheet.setColumnWidth(0, 10000);

row.setHeight((short) 1000);

设置字号、颜色和内容位置

HSSFCellStyle style = wb.createCellStyle();

HSSFFont f  = wb.createFont();

f.setFontHeightInPoints((short) 14);

f.setColor(HSSFFont.COLOR_RED);

style.setFont(f);

style.setAlignment(HSSFCellStyle.ALIGN_CENTER);

style.setVerticalAlignment(HSSFCellStyle.VERTICAL_CENTER);

合并单元格

sheet.addMergedRegion(new Region(1, (short) 1, 2, (short) 2));