Java Apache POI 创建双坐标轴折线图

Java Apache POI 创建双坐标轴折线图

本文提供使用 Java Apache POI 库创建包含双坐标轴的 Excel 折线图的详细代码示例，并提供针对可能出现的空指针异常的解决方案。

代码示例

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xddf.usermodel.chart.*;
import org.apache.poi.xssf.usermodel.*;
import org.openxmlformats.schemas.drawingml.x2006.chart.CTBoolean;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ExcelChartExample {

    public static void main(String[] args) {
        try {
            // 读取Excel文件
            FileInputStream fileIn = new FileInputStream('input.xlsx');
            XSSFWorkbook workbook = new XSSFWorkbook(fileIn);
            XSSFSheet sheet1 = workbook.getSheet('Sheet1');

            // 创建折线图
            XSSFDrawing drawing = sheet1.createDrawingPatriarch();
            XSSFClientAnchor anchor = drawing.createAnchor(0, 0, 0, 0, 0, 12, 10, 22);
            XDDFChart chart = drawing.createChart(anchor);
            chart.setTitleText('数据折线图');
            chart.setTitleOverlay(false);

            // 设置图例位置
            XDDFChartLegend legend = chart.getOrAddLegend();
            legend.setPosition(LegendPosition.BOTTOM);

            // 设置横坐标轴为日期坐标轴
            XDDFDataSource<?> dateSource = XDDFDataSourcesFactory.fromArray(new String[] {'A2:A127'});
            XDDFDateAxis bottomAxis = chart.createDateAxis(AxisPosition.BOTTOM);
            bottomAxis.setCrosses(AxisCrosses.AUTO_ZERO);
            bottomAxis.setTitle('时间');
            bottomAxis.setTickLabelPosition(AxisTickLabelPosition.NEXT_TO);

            // 设置时间格式
            SimpleDateFormat dateFormat = new SimpleDateFormat('yyyy/MM/dd');
            for (int i = 0; i < dateSource.getPointCount(); i++) {
                Row row = sheet1.getRow(i + 1);
                if (row != null) {
                    Cell cell = row.getCell(0);
                    if (cell != null && cell.getCellType() == CellType.NUMERIC) {
                        Date date = cell.getDateCellValue();
                        String formattedDate = dateFormat.format(date);
                        cell.setCellValue(formattedDate);
                    }
                }
            }

            // 设置左侧坐标轴为温度坐标轴
            XDDFValueAxis leftAxis = chart.createValueAxis(AxisPosition.LEFT);
            leftAxis.setCrosses(AxisCrosses.AUTO_ZERO);
            leftAxis.setTitle('温度');

            // 设置右侧坐标轴为数值坐标轴
            XDDFValueAxis rightAxis = chart.createValueAxis(AxisPosition.RIGHT);
            rightAxis.setCrosses(AxisCrosses.MAX);
            rightAxis.setTitle('数据值');

            // 设置数据源
            XDDFNumericalDataSource<Double> xs1 = XDDFDataSourcesFactory.fromNumericCellRange(sheet1, new CellRangeAddress(1, 127, 2, 2));
            XDDFNumericalDataSource<Double> ys1 = XDDFDataSourcesFactory.fromNumericCellRange(sheet1, new CellRangeAddress(1, 127, 0, 0));
            XDDFNumericalDataSource<Double> ys2 = XDDFDataSourcesFactory.fromNumericCellRange(sheet1, new CellRangeAddress(1, 127, 1, 1));

            // 添加数据系列
            XDDFLineChartData data = (XDDFLineChartData) chart.createData(ChartTypes.LINE, bottomAxis, leftAxis);
            XDDFLineChartData.Series series1 = (XDDFLineChartData.Series) data.addSeries(xs1, ys1);
            series1.setTitle('折线图1', null);
            series1.setSmooth(false);
            series1.setMarkerStyle(MarkerStyle.NONE);

            // 添加第二个数据系列
            XDDFLineChartData.Series series2 = (XDDFLineChartData.Series) data.addSeries(xs1, ys2);
            series2.setTitle('折线图2', null);
            series2.setSmooth(false);
            chart.getCTChart().getPlotArea().getLineChartArray(0).getSerArray(1).getOrder().setVal(1);

            // 设置次要垂直坐标轴
            CTBoolean ctBoolean = CTBoolean.Factory.newInstance();
            ctBoolean.setVal(false);
            CTDLbls dLbls = chart.getCTChart().getPlotArea().getLineChartArray(0).getSerArray(1).getDLbls();
            if (dLbls == null) {
                dLbls = chart.getCTChart().getPlotArea().getLineChartArray(0).getSerArray(1).addNewDLbls();
            }
            dLbls.setShowLegendKey(ctBoolean);
            dLbls.setShowVal(ctBoolean);
            dLbls.setShowCatName(ctBoolean);
            dLbls.setShowSerName(ctBoolean);

            // 保存Excel文件
            FileOutputStream fileOut = new FileOutputStream('output.xlsx');
            workbook.write(fileOut);
            fileOut.close();

            System.out.println('折线图已创建并保存到 output.xlsx 文件中。');

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

空指针异常解决方案

在上述代码中，设置次要垂直坐标轴的部分可能会出现空指针异常。这是因为 getDLbls() 方法可能返回 null。

为了解决这个问题，我们在调用 setShowLegendKey() 等方法之前，先判断 getDLbls() 返回的对象是否为空。如果为空，则需要创建一个新的 CTDLbls 对象。

CTDLbls dLbls = chart.getCTChart().getPlotArea().getLineChartArray(0).getSerArray(1).getDLbls();
if (dLbls == null) {
    dLbls = chart.getCTChart().getPlotArea().getLineChartArray(0).getSerArray(1).addNewDLbls();
}

通过添加这段代码，可以避免空指针异常的发生。