因公司项目需要，临时写的小程序。未优化，结构简单。

与上一版（https://my.oschina.net/u/3284390/blog/842084）相比的改进：

当待写出的数据为数字时，会自动转换单元格格式为数字（保留到小数点后两位）；

修改方法为静态方法，使用时无需初始化ToExcel类；

具体用法见上一版说明。

package tools;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.regex.Pattern;
import org.apache.poi.hssf.usermodel.HSSFCellStyle;
import org.apache.poi.hssf.usermodel.HSSFDataFormat;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
/**
 * 写出到Excel文件.
 * @author AL
 * 
 */
public class ToExcel {
	/**
	 * 匹配数字(非科学计数法).
	 */
	private static final Pattern general_num=Pattern.compile("^-{0,1}[0-9]+\\.{0,1}[0-9]*$");
	
	/**
	 * 匹配数字(科学计数法).
	 */
	private static final Pattern notation_num=Pattern.compile("^-{0,1}[0-9]+\\.{0,1}[0-9]*E{1}-{0,1}[0-9]+$");
	
	/**
	 * 逗号（英文输入状态）.
	 */
	private static final String comma =",";
	
	/**
	 * 等号（英文输入状态）.
	 */
	private static final String equal_sign ="=";

	/**
	 * 写出内容到Excel.
	 * map：key为Excel中每个分页的名称、List为分页的内容；
	 * fileName：最终输出的文件名，包含路径。
	 * @throws WriteExcelFailedException
	 * 
	 */
	public static<T> void toExcel(Map<String,List<T>> map,String fileName) throws WriteExcelFailedException {
		//新建文件输出流及Excel表格缓存区
		FileOutputStream out=null;
		HSSFWorkbook excel = null;
		try {
			out=new FileOutputStream(fileName+".xls");
			excel = new HSSFWorkbook();
		} catch (FileNotFoundException e) {
			throw new WriteExcelFailedException("未知的异常",e);
		}
		
		//此对象用于设置单元格格式为数字格式并保留小数点后两位，备用
		HSSFCellStyle cellStyle = excel.createCellStyle();
		cellStyle.setDataFormat(HSSFDataFormat.getBuiltinFormat("0.00"));
		
		//若map为空，则重构一个map，装入一个空白键值对
		if(map==null || map.isEmpty()){
			map=new HashMap<>();
			map.put("空", null);
		}
		
		//遍历键值对，将表格名称和表格内容传递给下一层，用于写出
		for(Entry<String, List<T>> entry : map.entrySet()){
			//向Excel（缓存区）内填充内容
			writeWorkbook(entry.getValue(),entry.getKey(),excel,cellStyle);
		}
		
		//写出到磁盘文件
		writeToDisk(out, excel);
	}
	
	/**
	 * 向Excel（缓存区）内填充内容.
	 * @param result
	 * @param sheetName
	 * @param excel
	 * @param cellStyle 
	 * 
	 */
	private static<T> void writeWorkbook(List<T> result, String sheetName, HSSFWorkbook excel, HSSFCellStyle cellStyle) {
		if(sheetName==null  || "".equals(sheetName)){//若sheetName为空，则填充“空”
			sheetName="空";
		}
		
		HSSFSheet sheet = excel.createSheet(sheetName);
		
		if (result == null || result.isEmpty()) {// 若集合为空，则写出“空”字符
			sheet.createRow(0).createCell(0).setCellValue("空");
			return;
		}
		
		//按照“,”将集合内元素toString的字符串切割成数组
		String[] temp = result.get(0).toString().split(comma);
		HSSFRow row = sheet.createRow(0);//获取此sheet表格的第一行
		int times=temp.length;
		for (int t = 0; t < times; t++) {//遍历数组，用于构造表头
			row.createCell(t).setCellValue(temp[t].substring(0, temp[t].indexOf(equal_sign)));//只取“=”之前的字符
		}
		
		//遍历集合，填充表格内容
		int size=result.size();
		for (int i = 1; i <= size; i++) {
			row = sheet.createRow(i);
			String[] infos=result.get(i - 1).toString().split(comma);//将toString返回的字符串按","切割成数组
			int round=infos.length;
			for (int j = 0; j < round; j++) {
				//只取“=”之后的字符
				String info =infos[j].substring(infos[j].indexOf(equal_sign) + 1, infos[j].length()).trim();

				//获取单元格
				Cell cell=row.createCell(j);
				
				//判断待输入的内容是否是数字
				if (general_num.matcher(info).matches() || notation_num.matcher(info).matches()) {
					cell.setCellStyle(cellStyle);
					cell.setCellValue(Double.parseDouble(info));
				}else{
					cell.setCellValue(info);
				}
			}
		}
	}
	
	/**
	 *  写出到磁盘文件.
	 * @param out
	 * @param excel
	 *
	 */
	private static void writeToDisk(FileOutputStream out, HSSFWorkbook excel) {
		try {
			excel.write(out);
			if(out!=null){//关闭流
				out.close();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
}

/**
 * 异常
 * @author AL
 *
 */
class WriteExcelFailedException extends Exception {
	private static final long serialVersionUID = 1L;

	public WriteExcelFailedException() {
		super();
	}

	public WriteExcelFailedException(String message, Throwable cause, boolean enableSuppression,
			boolean writableStackTrace) {
		super(message, cause, enableSuppression, writableStackTrace);
	}

	public WriteExcelFailedException(String message, Throwable cause) {
		super(message, cause);
	}

	public WriteExcelFailedException(String message) {
		super(message);
	}

	public WriteExcelFailedException(Throwable cause) {
		super(cause);
	}
}