向先原来就有数据的Excel写数据是不会覆盖原有的数据，只是在追加数据。
public class Excel {
public Excel() {
}
public void CreateWorkbook(File file, double[] a) {
try {
if (!file.exists()) { //判断文件是否已存在，如果没有存在则创建新文件
jxl.write.WritableWorkbook wwb = Workbook.createWorkbook(new
File("result.xls"
));
jxl.write.WritableSheet ws = wwb.createSheet("Test Sheet 1", 0);
int i = 0;
ws.setColumnView(0, 20); //设置列宽
jxl.write.NumberFormat nf = new jxl.write.NumberFormat(
"0.0000000000000000"); //定义数值格式
WritableCellFormat wcfN = new WritableCellFormat(nf);
String str2 = "第" + 1 + "次试验";
Label label = new Label(0, 0, str2);
ws.addCell(label);
while (i < a.length) {
jxl.write.Number num = new jxl.write.Number(0, i + 1,
a[i], wcfN);
ws.addCell(num);
i++;
}
//写入Exel工作表
wwb.write();
//关闭Excel工作薄对象
wwb.close();
} else {
Workbook rwb = Workbook.getWorkbook(file);
File tempfile = new File(System.getProperty("user.dir") +
"\\tempfile.xls");
WritableWorkbook wwb = Workbook.createWorkbook(tempfile, rwb);
WritableSheet ws = wwb.getSheet(0);
int num = rwb.getSheet(0).getColumns();
int num1 = num + 1;
ws.setColumnView(num, 20); //设置列宽
String str2 = "第" + num1 + "次试验"; //添加列名
Label label = new Label(num, 0, str2);
ws.addCell(label);
int i = 0;
jxl.write.NumberFormat nf = new jxl.write.NumberFormat(
"0.000000000000000"); //定义数值格式
WritableCellFormat wcfN = new WritableCellFormat(nf);
while (i < a.length) {
jxl.write.Number number = new jxl.write.Number(num,
i + 1,
a[i], wcfN);
ws.addCell(number);
i++;
}
wwb.write();
wwb.close();
rwb.close();
String filename = file.getPath();
System.out.println("filename:" + filename);
file.delete();
tempfile.renameTo(file);
System.out.println("tempfile:" + tempfile.getPath());
System.out.println(tempfile.exists());
System.out.println(file.exists());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}