import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
/*** * 基于POI的读写Excel文件的工具类* @author 彭锋* @2018年5月13日 下午4:00:11*/
public final class ExcelUtils {private static <T>Field[] getFields(Class<T> clazz,String[] fieldNames) {Field[] fs = new Field[fieldNames.length];Field[] fields = clazz.getDeclaredFields();for (int i = 0; i < fieldNames.length; i++) {O:for (Field field : fields) {field.setAccessible(true);if(field.getName().equals(fieldNames[i])) {fs[i] = field;break O;}}}System.out.println(Arrays.toString(fs));return fs;}private static <T>String[][] getDatas(String[] titles,List<T> beans,String[] fieldNames) throws Exception{List<String[]> datas = new ArrayList<>();if(titles != null && titles.length > 0) {datas.add(titles);}//根据List集合中的JavaBean对象的类型，和参数fieldNames，获取要写出的字段数组；Field[] fs = getFields(beans.get(0).getClass(),fieldNames);for (T t : beans) {String[] data = new String[fs.length];for (int i = 0; i < fs.length; i++) {if(fs[i] != null) {Object obj = fs[i].get(t);String value = obj == null ? "" : obj.toString();data[i] = value;}}datas.add(data);}return datas.toArray(new String[datas.size()][]);}/*** 将指定的二维字符串数组中的数据，写出到指定的Excel文件中* @param datas：保存了要写出的数据的二维数组；* @param output：关联到要输出的Excel文件的输出流* @throws IOException* @throws FileNotFoundException*/public static void writeToExcel(String[][] datas, OutputStream output) throws IOException, FileNotFoundException {// 创建一个Workbook对象；Workbook book = new HSSFWorkbook();// 通过workbook对象，创建一个工作表（sheet对象）Sheet sheet = book.createSheet();for (int i = 0; i < datas.length; i++) {// 通过工作表创建行Row row = sheet.createRow(i);for (int j = 0; j < datas[i].length; j++) {// 通过行创建单元格Cell cell = row.createCell(j);cell.setCellType(CellType.STRING);// 为单元格设置内容
                cell.setCellValue(datas[i][j]);}}book.write(output);book.close();}/*** 将指定集合中的所有JavaBean数据，写出到关联指定Excel文件的输出流中；* @param titles：输出的Excel文件的标题行的内容* @param fieldNames：一行中的各个列对应的JavaBean中的字段* @param beans：要输出的所有JavaBean对象* @param output：关联到指定Excel文件的输出流* @throws Exception*/public static <T>void writeToExcel(String[] titles,String[] fieldNames,List<T> beans,OutputStream output) throws Exception {String[][] datas = getDatas(titles, beans, fieldNames);writeToExcel(datas, output);}/*** 从指定的Excel的输入流中读取数据，写到指定类型的bean对象的List集合中；* @param input：关联到某个Excel文件的输入流* @param clazz：要封装一行数据的JavaBean的类型* @param fieldNames：一行数据中的列按顺序和JavaBean中对应的字段* @return* @throws Exception*/public static <T> List<T> readExcel(InputStream input, Class<T> clazz,String[] fieldNames) throws Exception {List<T> list = new ArrayList<>();Field[] fs = getFields(clazz,fieldNames);// 创建一个Workbook对象Workbook book = WorkbookFactory.create(input);// 通过Workbook对象，获取里面的工作表（sheet对象）Sheet sheet = book.getSheetAt(0);// 获取工作表中的行for (int i = 1; i <= sheet.getLastRowNum(); i++) {// 通过行号获取行Row row = sheet.getRow(i);T t = clazz.newInstance();// 遍历获取一行中的所有单元格for (int j = 0; j < fs.length; j++) {if(fs[j] != null) {Cell cell = row.getCell(j);cell.setCellType(CellType.STRING);setCellValue(fs[j],t,cell);}}list.add(t);}return list;}private static void setCellValue(Field field,Object bean,Cell cell) throws Exception {String str = cell.toString();Class clazz = field.getType();if(clazz == byte.class) {field.set(bean, Byte.parseByte(str));}else if(clazz == short.class) {field.set(bean, Short.parseShort(str));}else if(clazz == int.class) {field.set(bean, Integer.parseInt(str));}else if(clazz == long.class) {field.set(bean, Long.parseLong(str));}else if(clazz == double.class) {field.set(bean, Double.parseDouble(str));}else if(clazz == float.class) {field.set(bean, Float.parseFloat(str));}else if(clazz == boolean.class) {field.set(bean, Boolean.parseBoolean(str));}else {field.set(bean, str);}}
}