【每日一點】1. Java如何實現導出Excel單表頭或多表頭

一、背景在後臺項目中，經常會遇到將呈現的內容導出到Excel的需求，通過都是導出單個表頭的Excel文件，如果存在級聯關係的情況下，也就需要導出多表頭的場景。今天這篇文章就是分享導出Excel單表頭或多表頭的實現，目前實現方案僅支持2行表頭場景。如有更複雜的3行表頭、4行表頭複雜需求可以自行實現。 ...

一、背景

在後臺項目中，經常會遇到將呈現的內容導出到Excel的需求，通過都是導出單個表頭的Excel文件，如果存在級聯關係的情況下，也就需要導出多表頭的場景。今天這篇文章就是分享導出Excel單表頭或多表頭的實現，目前實現方案僅支持2行表頭場景。如有更複雜的3行表頭、4行表頭複雜需求可以自行實現。

二、實現思路

1. 藉助POI包實現表頭的寫入。每個表頭其實就是一行，如果是多個表頭，無非就是將寫多行表頭，然後將需要合併的表頭進行合併，藉助POI的函數為addMergedRegion。

2. 將導出數據進行轉化為一個集合，迴圈寫入每行數據。

三、實現代碼

3.1 pom引入

<properties>
        <java.version>1.8</java.version>
        <poi.version>3.17</poi.version>
        <mybatis.version>1.3.2</mybatis.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>${mybatis.version}</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>${poi.version}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>${poi.version}</version>
        </dependency>
    </dependencies>

View Code

3.2 Java代碼實現

@Getter
@Setter
public class ExcelHelper<T> {
    /**
     * 表格標題
     */
    private String title;

    /**
     * 單元格寬度
     */
    private int colWidth = 20;

    /**
     * 行高度
     */
    private int rowHeight = 20;

    private HSSFWorkbook workbook;

    /**
     * 表頭樣式
     */
    private HSSFCellStyle headStyle;

    /**
     * 主體樣式
     */
    private HSSFCellStyle bodyStyle;

    /**
     * 日期格式化,預設yyyy-MM-dd HH:mm:ss
     */
    private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    /**
     * Constructor
     * @param title
     */
    public ExcelHelper(String title){
        this.title = title;
        workbook = new HSSFWorkbook();
        init();
    }
    /**
     * Constructor
     * @param title
     * @param colWidth
     * @param rowHeight
     */
    public ExcelHelper(String title, int colWidth, int rowHeight){
        this.colWidth = colWidth;
        this.rowHeight = rowHeight;
        this.title = title;
        workbook = new HSSFWorkbook();
        init();
    }

    /**
     * Constructor
     * @param title
     * @param colWidth
     * @param rowHeight
     * @param dateFormat
     */
    public ExcelHelper(String title, int colWidth, int rowHeight, String dateFormat) {
        this.title = title;
        this.colWidth = colWidth;
        this.rowHeight = rowHeight;
        workbook = new HSSFWorkbook();
        sdf = new SimpleDateFormat(dateFormat);
        init();
    }

    /**
     * 導出Excel,適用於web導出excel
     *
     * @param sheet
     * @param data
     */
    private void writeSheet(HSSFSheet sheet, List<T> data,List<Column> headerList) {
        try {
            sheet.setDefaultColumnWidth(colWidth);
            sheet.setDefaultRowHeightInPoints(rowHeight);
            createHead(headerList, sheet);
            writeSheetContent(headerList, data, sheet);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * 導出表格
     * @param listColumn
     * @param datas
     * @return
     * @throws Exception
     */
    public InputStream exportExcel(List<Column> listColumn,List<T> datas) throws Exception {
        splitDataToSheets(datas,listColumn);
        return save(workbook);
    }

    /**
     * 導出表格 支持2級表頭或單表頭的Excel導出
     * @param headers
     * @param datas
     * @param filePath
     * @throws FileNotFoundException
     * @throws IOException
     * void
     */
    public void exportExcel(List<Column> headers,List<T> datas,String filePath) throws IOException {
        splitDataToSheets(datas, headers);
        save(workbook, filePath);
    }

    /**
     * 把數據寫入到單元格
     * @param listColumn
     * @param datas
     * @param sheet
     * @throws Exception
     * void
     */
    private void writeSheetContent(List<Column> listColumn,List<T> datas,HSSFSheet sheet) throws Exception {
        HSSFRow row;
        List<Column> listCol = getColumnList(listColumn);
        for (int i = 0, index = 2; i < datas.size(); i++, index++) {
            // 創建行
            row = sheet.createRow(index);
            for (int j = 0; j < listCol.size(); j++) {
                Column c = listCol.get(j);
                createCol(row, c, datas.get(i), j);
            }
        }
    }

    /**
     * 創建表頭
     * @param listColumn 表頭數組
     * @return 返回表頭總行數
     */
    public void createHead(List<Column> listColumn, HSSFSheet sheetCo){
        HSSFRow row = sheetCo.createRow(0);
        HSSFRow row2 = sheetCo.createRow(1);
        for(short i = 0, n = 0; i < listColumn.size(); i++){
            HSSFCell cell1 = row.createCell(n);
            cell1.setCellStyle(headStyle);
            HSSFRichTextString text;
            List<Column> columns = listColumn.get(i).getListColumn();
            //雙標題
            if(CollectionUtils.isEmpty(columns)){
                // 單標題
                HSSFCell cell2 = row2.createCell(n);
                cell2.setCellStyle(headStyle);
                text = new HSSFRichTextString(listColumn.get(i).getContent());
                sheetCo.addMergedRegion(new CellRangeAddress(0, n, 1, n));
                n++;
                cell1.setCellValue(text);
                continue;
            }

            text = new HSSFRichTextString(listColumn.get(i).getContent());
            cell1.setCellValue(text);

            // 創建第一行大標題
            sheetCo.addMergedRegion(new CellRangeAddress(0, 0, n, (short) (n + columns.size() -1)));
            // 給標題賦值
            for(int j = 0; j < columns.size(); j++){
                HSSFCell cell2 = row2.createCell(n++);
                cell2.setCellStyle(headStyle);
                cell2.setCellValue(new HSSFRichTextString(columns.get(j).getContent()));
            }
        }
    }

    /**
     * 創建行
     * @param row
     * @param column
     * @param v
     * @param rowIndex
     * @return
     * @throws Exception
     */
    public int createRowVal(HSSFRow row, Column column,T v,int rowIndex) throws Exception{
        // 遍歷標題
        if(column.getListColumn() != null && column.getListColumn().size() > 0){
            for(int i = 0; i < column.getListColumn().size(); i++){
                createRowVal(row,column.getListColumn().get(i),v,rowIndex);
            }
        }else{
            createCol(row,column,v,rowIndex++);
        }

        return rowIndex;
    }

    /**
     * 創建單元格
     * @param row
     * @param column
     * @param v
     * @param columnIndex
     * @throws Exception
     */
    public void createCol(HSSFRow row,Column column,T v,int columnIndex) throws Exception{
        // 創建單元格
        HSSFCell cell = row.createCell(columnIndex);
        // 設置單元格樣式
        cell.setCellStyle(bodyStyle);
        Class cls = v.getClass();
        Field field = cls.getDeclaredField(column.getFieldName());
        // 設置些屬性是可以訪問的
        field.setAccessible(true);
        if(field.get(v) != null){
            Object value = field.get(v);
            if(value instanceof Date){
                value = parseDate((Date)value);
            }

            HSSFRichTextString richString = new HSSFRichTextString(value.toString());
            cell.setCellValue(richString);
        }
    }

    /**
     * init
     */
    private void init(){
        // 生成表頭樣式
        headStyle = workbook.createCellStyle();
        headStyle.setFillForegroundColor(HSSFColor.HSSFColorPredefined.AQUA.getIndex());
        headStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        headStyle.setBorderBottom(BorderStyle.THIN);
        headStyle.setBorderLeft(BorderStyle.THIN);
        headStyle.setBorderRight(BorderStyle.THIN);
        headStyle.setBorderTop(BorderStyle.THIN);
        headStyle.setAlignment(HorizontalAlignment.CENTER);
        headStyle.setVerticalAlignment(VerticalAlignment.CENTER);

        // 生成一個字體
        HSSFFont headFont = workbook.createFont();
        headFont.setColor(HSSFColor.HSSFColorPredefined.VIOLET.getIndex());
        headFont.setFontHeightInPoints((short) 12);
        headFont.setBold(true);
        // 把字體應用到當前的樣式
        headStyle.setFont(headFont);

        // 生成並設置另一個樣式
        bodyStyle = workbook.createCellStyle();
        bodyStyle.setFillForegroundColor(HSSFColor.HSSFColorPredefined.WHITE.getIndex());
        bodyStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        bodyStyle.setBorderBottom(BorderStyle.THIN);
        bodyStyle.setBorderLeft(BorderStyle.THIN);
        bodyStyle.setBorderRight(BorderStyle.THIN);
        bodyStyle.setBorderTop(BorderStyle.THIN);
        bodyStyle.setAlignment(HorizontalAlignment.CENTER);
        bodyStyle.setVerticalAlignment(VerticalAlignment.CENTER);

        // 生成另一個字體
        HSSFFont bodyFont = workbook.createFont();
        bodyFont.setBold(false);
        // 把字體應用到當前的樣式
        bodyStyle.setFont(bodyFont);
    }

    /**
     * 時間轉換
     * @param date
     * @return
     * String
     */
    private  String parseDate(Date date){
        String dateStr = "";
        try{
            dateStr = sdf.format(date);
        } catch (Exception e){
            e.printStackTrace();
        }

        return dateStr;
    }

    /**
     * 拆分sheet，因為每個sheet不能超過6526，否則會報異常
     * @param data
     * @param listColumn
     * void
     */
    private void splitDataToSheets(List<T> data,List<Column> listColumn) {
        int dataCount = data.size();
        int maxColumn = 65535;
        int pieces = dataCount / maxColumn;
        for (int i = 1; i <= pieces; i++) {
            HSSFSheet sheet = workbook.createSheet(this.title + i);
            List<T> subList = data.subList((i - 1) * maxColumn, i * maxColumn);
            writeSheet(sheet, subList, listColumn);
        }

        HSSFSheet sheet = workbook.createSheet(this.title + (pieces + 1));
        writeSheet(sheet, data.subList(pieces * maxColumn, dataCount), listColumn);
    }

    /**
     * 把column的columnList整理成一個list<column>
     * @param listColumn
     * @return
     * List<Column>
     */
    private List<Column> getColumnList(List<Column> listColumn){
        List<Column> listCol = new ArrayList<>();
        for(int i = 0; i < listColumn.size(); i++){
            List<Column> list = listColumn.get(i).getListColumn();
            if(list.size() > 0){
                for(Column c : list){
                    if(c.getFieldName() != null){
                        listCol.add(c);
                    }
                }
            }else{
                if(listColumn.get(i).getFieldName() != null){
                    listCol.add(listColumn.get(i));
                }
            }
        }

        return listCol;
    }

    /**
     * 保存Excel到InputStream，此方法適合web導出excel
     *
     * @param workbook
     * @return
     */
    private InputStream save(HSSFWorkbook workbook) {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            workbook.write(bos);
            InputStream bis = new ByteArrayInputStream(bos.toByteArray());
            return bis;
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    /**
     * 保存文件
     * @param workbook
     * @param filePath
     * @throws IOException
     */
    private void save(HSSFWorkbook workbook,String filePath) throws IOException {
        workbook.write(new FileOutputStream(filePath));
    }

四、測試類

public class ExportTest {
    @Data
    @AllArgsConstructor
    public class ValueObj {
        private String value1;

        private String value2;
    }
    public static void main(String[] args) throws Exception {

        //用於存放第一行單元格
        List<Column> listColumn = new ArrayList<>();
        // 用於存放第一列第二行的單元格
        List<Column> list2 = new ArrayList<>();
        // 創建一列，value1 表示這一列需要導出欄位的值
        list2.add(new Column("標題1","value1"));
        list2.add(new Column("標題2","value1"));
        list2.add(new Column("標題3","value1"));

        // 用於存放第二列第二行的單元格
        List<Column> list3  = new ArrayList<>();
        list3.add(new Column("標題6","value2"));
        list3.add(new Column("標題7","value2"));


        //創建第一行大標題,大標題的fieldName 為 null
        Column c1 = new Column("標題1",null);
        c1.setListColumn(list2);
        Column c2 = new Column("標題2",null);
        c2.setListColumn(list3);
        listColumn.add(c1);
        listColumn.add(c2);

        //需要導出的數據
        List<ValueObj> valueList = new ArrayList<>();
        valueList.add(new ValueObj("1","11"));
        valueList.add(new ValueObj("2","22"));
        valueList.add(new ValueObj("3","33"));
        valueList.add(new ValueObj("4","44"));

        ExcelHelper<ValueObj> ta = new ExcelHelper<ValueObj>("表格",15,20);
        ta.exportExcel(listColumn, valueList,"D:\\outExcel.xls");
    }
}