Java实现集合和Excel文件相互转换-编程知识

一、集合转化为Excel文件

效果如下，是将集合转化为Excel文件，Excel包含合并单元格。
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实体类：

@Data
public class ClassGrade {/** 年级 */private String grade;/** 班主任 */private String leader;/** 学生列表 */private List<Student> students;@Datapublic static class Student {/** 姓名 */private String name;/** 年龄 */private Integer age;/** 性别 */private String sex;/** 成绩 */private Integer gradeResult;}
}

需求就是将ClassGrade的集合转化为Excel表格对外输出。没有针对当前类去逐个取值处理，用到了反射来处理，达到了简化代码通用的目的。这个只针对有一个合并单元格的情形，如果是合并单元格中包含合并单元格的话，还需要加代码去处理。
实现代码如下：
1.初始化表头类，参数为表头集合

    public static SXSSFWorkbook makeExcelHead(String[] titles) {SXSSFWorkbook workbook = new SXSSFWorkbook();CellStyle styleTitle = getTitleStyle(workbook, (short) 16);SXSSFSheet sheet = workbook.createSheet();SXSSFRow rowTitle = sheet.createRow(0);for (int i = 0; i < titles.length; i++) {sheet.setDefaultColumnWidth(25);SXSSFCell cellTitle = rowTitle.createCell(i);// 为标题设置背景颜色styleTitle.setFillPattern(FillPatternType.SOLID_FOREGROUND);styleTitle.setFillForegroundColor(HSSFColor.HSSFColorPredefined.GREY_25_PERCENT.getIndex());cellTitle.setCellValue(titles[i]);cellTitle.setCellStyle(styleTitle);}return workbook;}

2.反射获取实体的值

    public static <T> Object getProperty(T t, String propertyName) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, IndexOutOfBoundsException {Class<?> aClass = t.getClass();propertyName = propertyName.substring(0, 1).toUpperCase() + propertyName.substring(1);Method method = aClass.getMethod("get" + propertyName);Object invoke = method.invoke(t);return invoke;}

2.将集合转化为Excel

    @Testpublic void exportExcel() throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {//初始化数据List<ClassGrade> fileList = new ArrayList<>();for (int m = 1; m <= 1; m++) {fileList.addAll(getGrades());}//表头名称String[] title = {"班主任", "学生姓名", "学生年龄", "学生性别", "学生成绩", "班级"};SXSSFWorkbook workbook = SXSSFWorkbookUtil.makeExcelHead(title);//每一列表头属性，如果子类里面的，则提取子类里面对应的属性名String[] properties = {"leader", "name", "age", "sex", "gradeResult", "grade"};//获取当前sheetSXSSFSheet sheet = workbook.getSheetAt(0);int initRowNum = 0;//遍历数据，需要根据业务逻辑去处理是否合并单元格for (int i = 0; i < fileList.size(); i++) {ClassGrade file = fileList.get(i);int size = file.getStudents().size();//创建行，以子类的集合数为准int startRowNum = initRowNum + 1;int lastRowNum = startRowNum + size - 1;SXSSFRow row = sheet.getRow(startRowNum);if (row == null) {row = sheet.createRow(startRowNum);}//班主任一列，处理合并单元格for (int m = 0; m < 1; m++) {if (lastRowNum - startRowNum > 0) {sheet.addMergedRegion(new CellRangeAddress(startRowNum, lastRowNum, m, m));}createCell(row, m, SXSSFWorkbookUtil.getProperty(file, properties[m]));}//处理学生姓名~学生成绩四列，非合并单元格信息int xRowNum = startRowNum;List<ClassGrade.Student> receiptItems = file.getStudents();for (ClassGrade.Student student : receiptItems) {SXSSFRow row1 = sheet.getRow(xRowNum);if (row1 == null) {row1 = sheet.createRow(xRowNum);}for (int q = 1; q <= 4; q++) {//利用反射获取到值，并且设置到cell里面createCell(row1, q, SXSSFWorkbookUtil.getProperty(student, properties[q]));}xRowNum++;}//处理班级信息合并单元格for (int n = 5; n <= 5; n++) {if (lastRowNum - startRowNum >= 1) {sheet.addMergedRegion(new CellRangeAddress(startRowNum, lastRowNum, n, n));}createCell(row, n, SXSSFWorkbookUtil.getProperty(file, properties[n]));}initRowNum = lastRowNum;}//导出try (FileOutputStream excel = new FileOutputStream("excel.xls");BufferedOutputStream bos = new BufferedOutputStream(excel)) {workbook.write(bos);System.out.println("导出完成");} catch (IOException e) {System.out.println("导出失败:" + e.getMessage());}}private void createCell(SXSSFRow row, int column, Object value) {SXSSFCell cell = row.createCell(column);if (value != null) {cell.setCellValue(String.valueOf(value));}}

效果
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二、Excel文件转化为集合

如题，将获取到的excel文件流转化为集合进行处理。挺简单的。思路就是将一个文件流转化为一个备用类，再将备用类转化为想要的集合。
excel：
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备用类代码：

@Data
public class ClassGrade2 {/** 年级 */private String grade;/** 班主任 */private String leader;/** 姓名 */private String name;/** 年龄 */private Integer age;/** 性别 */private String sex;/** 成绩 */private Integer gradeResult;
}

转化代码：

    @Testpublic void test1() {ExcelReader reader = ExcelUtil.getReader("excelToList.xls");List<List<Object>> rows = reader.read();//根据excel的结构，需要准备一个备用类接收数据List<ClassGrade2> listBaks = new ArrayList<>();//初始化属性，属性是备用类的属性名String[] properties = {"leader", "name", "age", "sex", "gradeResult", "grade"};for (int j = 1; j < rows.size(); j++) {List<Object> cells = rows.get(j);try {//反射获取值，组装成备用类ClassGrade2 file = new ClassGrade2();Class<?> clz = file.getClass();Method[] methods = clz.getDeclaredMethods();for (int i = 0; i < cells.size(); i++) {String propertyName = properties[i].substring(0, 1).toUpperCase() + properties[i].substring(1);Method method = Arrays.stream(methods).filter(m -> Objects.equal(m.getName(), "set" + propertyName)).findFirst().orElse(null);Object cell = cells.get(i);if (cell == null) {continue;}Field field = clz.getDeclaredField(properties[i]);String fieldType = field.getType().getName();if (fieldType.equals("java.lang.String")) {method.invoke(file, String.valueOf(cell));} else if (fieldType.equals("java.math.BigDecimal")) {method.invoke(file, new BigDecimal(String.valueOf(cell)));}}listBaks.add(file);} catch (IllegalAccessException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();} catch (NoSuchFieldException e) {e.printStackTrace();} finally {}}//备用类转化为想要的集合类int i = 0;List<ClassGrade> files = new ArrayList<>();for (int m = 0; m < listBaks.size(); m++) {ClassGrade2 fileBak = listBaks.get(m);if (Strings.isNotEmpty(fileBak.getGrade())) {ClassGrade file = BeanUtil.copyProperties(fileBak, ClassGrade.class);files.add(file);ClassGrade.Student item = BeanUtil.copyProperties(fileBak, ClassGrade.Student.class);List<ClassGrade.Student> items = new ArrayList<>();items.add(item);file.setStudents(items);i++;} else {ClassGrade.Student item = BeanUtil.copyProperties(fileBak, ClassGrade.Student.class);ClassGrade file = files.get(i - 1);List<ClassGrade.Student> items = CollectionUtils.isEmpty(file.getStudents()) ? new ArrayList<>() : file.getStudents();items.add(item);file.setStudents(items);}}log.info("{}", JSONArray.toJSONString(listBaks));log.info("{}", JSONArray.toJSONString(files));}

实现效果：

11:47:03.635 [main] INFO Excel3Test - [{"grade":"八年级1班","leader":"赵老师","name":"张三","sex":"女"},{"grade":"八年级1班","leader":"赵老师","name":"李四","sex":"女"},{"grade":"八年级1班","leader":"赵老师","name":"王五","sex":"女"}]
11:47:03.647 [main] INFO Excel3Test - [{"grade":"八年级1班","leader":"赵老师","students":[{"name":"张三","sex":"女"}]},{"grade":"八年级1班","leader":"赵老师","students":[{"name":"李四","sex":"女"}]},{"grade":"八年级1班","leader":"赵老师","students":[{"name":"王五","sex":"女"}]}]