java导出Excel文件的步骤全纪录

String[][] header = {
 {"field1","参数1"}
 ，{"field2","参数2"}
 ，{"field3","参数3"}
}

public class A{
 private String name;
 private String address;
}
public class B{
 private int id;
 private double sum;
 private String cat;
}

String[][] sheetA = {
 {"name","姓名"}
 ,{"address","住址"}
}
String[][] sheetB = {
 {"id","ID"}
 ,{"sum","余额"}
 ,{"cat","猫的名字"}
}

String fileName = "测试Excel";
HashMap<String,List<?>> data = new HashMap<>();
//ASheet为表名，后面headers里的key要跟这里一致
data.put("ASheet",dataA);
data.put("BSheet",dataB);
LinkedHashMap<String,String[][]> headers = new LinkedHashMap<>();
headers.put("ASheet",sheetA);
headers.put("BSheet",sheetB);
ExcelUtil excelUtil = new ExcelUtil(fileName,data,headers);
//获取表格对象
HSSFWorkbook workbook = excelUtil.createExcel();
//这里内置了一个写到response的方法（判断浏览器类型设置合适的参数），如果想写到文件也是类似的
workbook.writeToResponse(workbook,request,response);

 public HSSFWorkbook createExcel() throws Exception {
  try {
   HSSFWorkbook workbook = new HSSFWorkbook();
   //遍历headers创建表格
   for (String key : headers.keySet()) {
    this.createSheet(workbook, key, headers.get(key), this.data.get(key));
   }
   return workbook;
  } catch (Exception e) {
   log.error("创建表格失败:{}", e.getMessage());
   throw e;
  }
 }

  HSSFSheet sheet = workbook.createSheet(sheetName);
  // 列数
  int cellNum = header.length;
  // 单元行，单元格
  HSSFRow row;
  HSSFCell cell;
  // 表头单元格样式
  HSSFCellStyle columnTopStyle = this.getColumnTopStyle(workbook);
  // 设置表头
  row = sheet.createRow(0);
  for (int i = 0; i < cellNum; i++) {
   cell = row.createCell(i);
   cell.setCellStyle(columnTopStyle);
   String str = header[i][1];
   cell.setCellValue(str);
   // 设置列宽为表头的文字宽度+6个半角符号宽度
   sheet.setColumnWidth(i, (str.getBytes("utf-8").length + 6) * 256);
  }

/**
 * 设置单元格,根据fieldName获取对应的Field类，使用反射得到值
 *
 * @param cell 单元格实例
 * @param obj 存有属性的对象实例
 * @param fieldMap 属性名与Field的映射
 * @param fieldName 属性名
 */
private void setCell(HSSFCell cell, Object obj, Map<String, Field> fieldMap, String fieldName) throws Exception {
 //获取该属性的Field对象
 Field field = fieldMap.get(fieldName);
 //通过反射获取属性的值，由于不能确定该值的类型，用下面的判断语句进行合适的转型
 Object value = field.get(obj);
 if (value == null) {
  cell.setCellValue("");
 } else {
  switch (field.getGenericType().getTypeName()) {
  case "java.lang.String":
   cell.setCellValue((String) value);
   break;
  case "java.lang.Integer":
  case "int":
   cell.setCellValue((int) value);
   break;
  case "java.lang.Double":
  case "double":
   cell.setCellValue((double) value);
   break;
  case "java.util.Date":
   cell.setCellValue(this.dateFormat.format((Date) value));
   break;
  default:
   cell.setCellValue(obj.toString());
  }
 }
}