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));