(7) 如何用Apache POI操作Excel文件-----如何用Apache POI 画一个离散图

有的时候，我们需要Excel中的数据，通过一个图画，可视化的表现出来。 那么这个时候，应该如何做呢？现在就借花献佛，以Apache POI自己提供的一个例子为例，给大家演示一下POI的API 如何画图的。下面是一个最终的效果图。然后分别给大家解释每段代码的作用和意义。

代码如下，

import java.io.FileOutputStream;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.*;
import org.apache.poi.ss.usermodel.charts.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

/**
 * Illustrates how to create a simple scatter chart.
 *
 * @author Roman Kashitsyn
 */
public class ScatterChart {

    public static void main(String[] args) throws Exception {
        Workbook wb = new XSSFWorkbook();
        Sheet sheet = wb.createSheet("Sheet 1");
        final int NUM_OF_ROWS = 3;
        final int NUM_OF_COLUMNS = 10;

        // Create a row and put some cells in it. Rows are 0 based.
        Row row;
        Cell cell;
        for (int rowIndex = 0; rowIndex < NUM_OF_ROWS; rowIndex++) {
            row = sheet.createRow((short) rowIndex);
            for (int colIndex = 0; colIndex < NUM_OF_COLUMNS; colIndex++) {
                cell = row.createCell((short) colIndex);
                cell.setCellValue(colIndex * (rowIndex + 1));
            }
        }

        Drawing drawing = sheet.createDrawingPatriarch();
        ClientAnchor anchor = drawing.createAnchor(0, 0, 0, 0, 0, 5, 10, 15);

        Chart chart = drawing.createChart(anchor);
        ChartLegend legend = chart.getOrCreateLegend();
        legend.setPosition(LegendPosition.TOP_RIGHT);

        ScatterChartData data = chart.getChartDataFactory().createScatterChartData();

        ValueAxis bottomAxis = chart.getChartAxisFactory().createValueAxis(AxisPosition.BOTTOM);
        ValueAxis leftAxis = chart.getChartAxisFactory().createValueAxis(AxisPosition.LEFT);
        leftAxis.setCrosses(AxisCrosses.AUTO_ZERO);

        ChartDataSource<Number> xs = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(0, 0, 0, NUM_OF_COLUMNS - 1));
        ChartDataSource<Number> ys1 = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(1, 1, 0, NUM_OF_COLUMNS - 1));
        ChartDataSource<Number> ys2 = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(2, 2, 0, NUM_OF_COLUMNS - 1));

        data.addSerie(xs, ys1);
        data.addSerie(xs, ys2);

        chart.plot(data, bottomAxis, leftAxis);

        // Write the output to a file
        FileOutputStream fileOut = new FileOutputStream("ooxml-scatter-chart.xlsx");
        wb.write(fileOut);
        fileOut.close();
    }
}

下面逐一来分解：

1.下面的代码新建一个工作簿和工作表单的对象

   Workbook wb = new XSSFWorkbook();
        Sheet sheet = wb.createSheet("Sheet 1");

2.下面这段代码是用生成初始化数据的，总共的数据有3行10列。

 final int NUM_OF_ROWS = 3;
 final int NUM_OF_COLUMNS = 10;

        // Create a row and put some cells in it. Rows are 0 based.
        Row row;
        Cell cell;
        for (int rowIndex = 0; rowIndex < NUM_OF_ROWS; rowIndex++) {
            row = sheet.createRow((short) rowIndex);
            for (int colIndex = 0; colIndex < NUM_OF_COLUMNS; colIndex++) {
                cell = row.createCell((short) colIndex);
                cell.setCellValue(colIndex * (rowIndex + 1));
            }
        }

3. 下面这段代码设置了画图的区域：从第5行开始，到15行结束；总共占用10列

Drawing drawing = sheet.createDrawingPatriarch();
ClientAnchor anchor = drawing.createAnchor(0, 0, 0, 0, 0, 5, 10, 15);

4.创建一个离散图的坐标系

 Chart chart = drawing.createChart(anchor);
 ChartLegend legend = chart.getOrCreateLegend();
 legend.setPosition(LegendPosition.TOP_RIGHT);

 ScatterChartData data = chart.getChartDataFactory().createScatterChartData();

 ValueAxis bottomAxis = chart.getChartAxisFactory().createValueAxis(AxisPosition.BOTTOM);
 ValueAxis leftAxis = chart.getChartAxisFactory().createValueAxis(AxisPosition.LEFT);
 leftAxis.setCrosses(AxisCrosses.AUTO_ZERO);

5.往离散图上填充数据

 ChartDataSource<Number> xs = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(0, 0, 0, NUM_OF_COLUMNS - 1));
 ChartDataSource<Number> ys1 = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(1, 1, 0, NUM_OF_COLUMNS - 1));
 ChartDataSource<Number> ys2 = DataSources.fromNumericCellRange(sheet, new CellRangeAddress(2, 2, 0, NUM_OF_COLUMNS - 1));

 data.addSerie(xs, ys1);
 data.addSerie(xs, ys2);

其中，下面的方法定义

DataSources.fromNumericCellRange(sheet, new CellRangeAddress(0, 0, 0, NUM_OF_COLUMNS - 1));

如下，

 public static ChartDataSource<Number> fromNumericCellRange(Sheet sheet, CellRangeAddress cellRangeAddress) 

从上面可以看出，其实填充数据的关键方法是，

<pre name="code" class="java">new CellRangeAddress(0, 0, 0, NUM_OF_COLUMNS - 1)

那么这个方式是如何定义的呢？

public CellRangeAddress(int firstRow, int lastRow, int firstCol, int lastCol)

从上面可以看出，其让我们制定数据是从那一行开始的，那一行结束的，那一列开始的，那一列结束。

在上面的代码的5句话中，分别把第1行的1到10列做为基准，然后把第2行的1到10列做一个比较，画出曲线系列1

把第1行的1到10列做为基准，然后把第3行的1到10列做一个比较，画出曲线系列2

6. 开始画图

chart.plot(data, bottomAxis, leftAxis);

7. 保存成一个Excel文件

 FileOutputStream fileOut = new FileOutputStream("ooxml-scatter-chart.xlsx");
 wb.write(fileOut);
 fileOut.close();