使用POI将数据库导出为excel表格

准备

使用的是POI,是Apache项目,目前已经很少有人用jxl了,学就学习常用的东西,没有必要去学冷门.
此种方式使用的map封装的数据,操作比较的简单使用的是mybatis+map的方式.
另有一种方式略微复杂,使用jdbc+list,效率高些: https://blog.csdn.net/sqlgao22/article/details/100736325

数据库

        <!--操作xls类型文件--><dependency><groupId>org.apache.poi</groupId><artifactId>poi</artifactId><version>3.17</version></dependency><!--操作xlsx类型文件--><dependency><groupId>org.apache.poi</groupId><artifactId>poi-ooxml</artifactId><version>3.17</version></dependency>

思路

将数据库中的内容全部取出存到实体类的list中,
将表格的一行看作是一个实体类的映射,表头是实体类的属性,因此,重要的是将实体类转换为map集合,才能取出map中的key.
幸运的是,我们不用自己去反射去组合,spring框架中有一个很好的工具类:
org.springframework.cglib.beans.BeanMap,可以方便的使用.
我将方法做了简单的封装,可以使用.

public class MapAndBeanUtil {/*** 将实体类转换为一个Map*/public static <T> Map<String,Object> beanToMap (T bean) {Map<String, Object> map = new HashMap<>();//创建一个BeanMapBeanMap beanMap = BeanMap.create(bean);//将BeanMap转换为MapIterator iterator = beanMap.keySet().iterator();while (iterator.hasNext()) {String key = (String) iterator.next();map.put(key, beanMap.get(key));}return map;}/*** 实体类集合转换为List<Map>*/public static <T> List<Map<String, Object>> beansToMap(List<T> beanList) {List<Map<String, Object>> mapList = new ArrayList<>();Iterator<T> iterator = beanList.iterator();while (iterator.hasNext()) {T bean = iterator.next();Map<String, Object> map = beanToMap(bean);mapList.add(map);}return mapList;}/*** 将map转化为实体类*/public static <T> T mapToBean(Map<String, Object> map,Class<T> clazz) throws IllegalAccessException, InstantiationException {T bean = clazz.newInstance();BeanMap beanMap = BeanMap.create(bean);//将map转换为beanbeanMap.putAll(map);return bean;}/*** 将List<Map>转化为实体类*/public static <T> List<T> mapsToBeans(List<Map<String, Object>> mapList,Class<T> clazz) throws IllegalAccessException, InstantiationException {List<T> list = new ArrayList<>();Iterator<Map<String, Object>> iterator = mapList.iterator();while (iterator.hasNext()) {Map<String, Object> map = iterator.next();T bean = mapToBean(map, clazz);list.add(bean);}return list;}
}

实现

有两种方式实现,:
方式一:创建一个新的文件,只需要指定文件的路径即可,
方式二:直接准备一个excel将数据写入.

先看方式一

public class CreatExcel {public static void writeExcel(List<Map<String,Object>> dataList,String filePath) throws Exception {//创建文件File path = new File(filePath);if (!path.exists()) {path.mkdirs();}String fileName = System.currentTimeMillis() + ".xlsx";File file = new File(path, fileName);//创建一个excel对象Workbook workbook = new XSSFWorkbook();//创建第一个工作簿Sheet sheet = workbook.createSheet("dbName");//将数据库字段（map的key）写入第一行Map<String, Object> firstRowMap = dataList.get(0);Set<String> keySet = firstRowMap.keySet();Object[] keyArr = keySet.toArray();Row row0 = sheet.createRow(0);for (int i = 0; i < keyArr.length; i++) {//创建单元格并写入数据Cell cell = row0.createCell(i);cell.setCellValue(keyArr[i].toString());}//将数据写入其他行for (int i = 0; i < dataList.size(); i++) {//控制有多少行Map<String, Object> rowMap = dataList.get(i);Row row = sheet.createRow(i + 1);for (int j = 0; j < rowMap.size(); j++) {Cell cell = row.createCell(j);Object o = rowMap.get((String) keyArr[j]);//除掉空值,也可以写入对应类型,此处直接写入stringcell.setCellValue(null==o?"":o.toString());}}//输出文件FileOutputStream fos = new FileOutputStream(file);workbook.write(fos);}
}

测试

读取数据库的代码就不放了.

    @Testpublic void Test01() throws Exception {List<User> allUser = userController.getAllUser();List<Map<String, Object>> mapList = MapAndBeanUtil.beansToMap(allUser);CreatExcel.writeExcel(mapList,"d://222222/333/444");}

导出的结果就是这样,文件也生成了.顺序需要自己调整.
原因相信不用我说,都知道.

方式二

方式二:直接准备一个excel将数据写入.方法大同小异

public class WriteExcel {public static void writeExcel(List<Map<String,Object>> dataList,File file) throws Exception {//判断文件类型获取文件Workbook workbook = getWorkbook(file);//获取第一个工作簿Sheet sheet = workbook.getSheetAt(0);//清除表内的原有的数据for (int i = 0; i < sheet.getLastRowNum(); i++) {Row row = sheet.getRow(i);if (null!=row) {sheet.removeRow(row);}}//将数据库字段（map的key）写入第一行Map<String, Object> firstRowMap = dataList.get(0);Set<String> keySet = firstRowMap.keySet();Object[] keyArr = keySet.toArray();Row row0 = sheet.createRow(0);for (int i = 0; i < keyArr.length; i++) {row0.createCell(i).setCellValue(keyArr[i].toString());}//将数据写入其他行for (int i = 0; i < dataList.size(); i++) {//控制有多少行Map<String, Object> rowMap = dataList.get(i);Row row = sheet.createRow(i + 1);for (int j = 0; j < rowMap.size(); j++) {Cell cell = row.createCell(j);System.out.println(keyArr[j]);cell.setCellValue(null==(rowMap.get((String)keyArr[j]))?"":rowMap.get(keyArr[j]).toString());}}//输出文件FileOutputStream fos = new FileOutputStream(file);workbook.write(fos);}private static Workbook getWorkbook(File file) throws Exception {Workbook workbook = null;FileInputStream fis = new FileInputStream(file);if (file.getName().endsWith("xls")) {workbook = new HSSFWorkbook(fis);} else if (file.getName().endsWith("xlsx")) {workbook = new XSSFWorkbook(fis);} else {throw new Exception("格式错误");}return workbook;}
}

结果同样写入.