2015/12/21
今天的任务是读写excel,参考了这篇博客

用到了apache的poi解析：
HSSFWorkbook 对应excel文件；

//读取方法。
HSSFWorkbook hssfWorkbook = new HSSFWorkbook(InputStream  is);
//创建方法
HSSFWorkbook hssfWorkbook = new HSSFWorkbook();
```
HSSFSheet 对应excel里的页；
````java
//读取方法。
HSSFSheet hssfSheet = hssfWorkbook.getSheetAt(numSheet);
//创建方法
HSSFSheet hssfSheet = hssfWorkbook.createSheet("sheetName");
```
HSSFRow 对应excel里的行；
````java
//读取方法。
/*getCell(int num);
*获取hssfRow里的cell对象。
*/
hssfRow.getCell(0);
//创建方法
HSSFCell hssfCell = row.createCell(int num);
```
HSSFCell 对应excel里具体的格子。
````java
//读取方法。
HSSFCell hssfCell = hssfRow.getCell(int num);
//创建方法
HSSFWorkbook hssfWorkbook = new HSSFWorkbook();
OutputStream out = new FileOutputStream("路径"); hssfWorkbook.write(out);
```
以下是poi中的常用方法
````java
/*write(OutputStream out)
*根据文件输出流，输出hssfWorkbook。
*/
OutputStream out = new FileOutputStream("路径"); hssfWorkbook.write(out);
/*getNumberOfSheets()
*获取hssfWorkbook里的页数。
*/
 hssfWorkbook.getNumberOfSheets();
/*getLastRowNum();
*获取hssfSheet里的行数。
*/
 hssfSheet.getLastRowNum();
/*判断hssfcell的属性
*
*/
hssfCell.getCellType()；
 /**
     * Numeric Cell type (0)
     * @see #setCellType(int)
     * @see #getCellType()
     */
    public final static int CELL_TYPE_NUMERIC = 0;

    /**
     * String Cell type (1)
     */
    public final static int CELL_TYPE_STRING = 1;

    /**
     * Formula Cell type (2)
     */
    public final static int CELL_TYPE_FORMULA = 2;

    /**
     * Blank Cell type (3)
     */
    public final static int CELL_TYPE_BLANK = 3;

    /**
     * Boolean Cell type (4)
     */
    public final static int CELL_TYPE_BOOLEAN = 4;

    /**
     * Error Cell type (5)
     */
    public final static int CELL_TYPE_ERROR = 5;
```

这是读取Excel的部分
````java
    public List<Student> readXls() throws IOException {
        InputStream is = new FileInputStream(Common.EXCEL_PATH);//EXCEL_PATH存放路径
        HSSFWorkbook hssfWorkbook = new HSSFWorkbook(is);
        Student student = null;
        List<Student> list = new ArrayList<Student>();
        // 循环工作表Sheet
        for (int numSheet = 0; numSheet < hssfWorkbook.getNumberOfSheets(); numSheet++) {
            HSSFSheet hssfSheet = hssfWorkbook.getSheetAt(numSheet);
            if (hssfSheet == null) {
                continue;
            }
            // 循环行Row,第一行是列名，所以跳过
            for (int rowNum = 1; rowNum <= hssfSheet.getLastRowNum(); rowNum++) {
                HSSFRow hssfRow = hssfSheet.getRow(rowNum);
                if (hssfRow != null) {
                    student = new Student();
                    HSSFCell no = hssfRow.getCell(0);
                    HSSFCell name = hssfRow.getCell(1);
                    HSSFCell lastName = hssfRow.getCell(2);
                    HSSFCell age = hssfRow.getCell(3);
                    HSSFCell score = hssfRow.getCell(4);
                    student.setNo(getValue(no));
                    student.setName(getValue(name)+" "+getValue(lastName));
                    student.setAge(getValue(age));
                    student.setScore(Float.valueOf(getValue(score)));
                    list.add(student);
                }
            }
        }
        return list;
    }
```
我们需要一个函数去判断excel里数据的类型
````java
    private String getValue(HSSFCell hssfCell) {
         if(hssfCell!= null){
            if (hssfCell.getCellType() == hssfCell.CELL_TYPE_BOOLEAN) {
                // 返回布尔类型的值
                return String.valueOf(hssfCell.getBooleanCellValue());
            } else if (hssfCell.getCellType() == hssfCell.CELL_TYPE_NUMERIC) {
                // 返回数值类型的值
                return String.valueOf(hssfCell.getNumericCellValue());
            } else {
                // 返回字符串类型的值
                return String.valueOf(hssfCell.getStringCellValue());
            }
        }else{
            return "";
        }
     }
```
下面是导入excel的代码
````java
 public static void writeExcel(List<Student> xls) throws Exception {
      // 获取总列数
      int CountColumnNum = xls.size();
      // 创建Excel文档
      HSSFWorkbook hssfWorkbook = new HSSFWorkbook();
      Student student = null;
      // sheet 对应一个工作页
      HSSFSheet sheet = hssfWorkbook.createSheet("第一页");
      HSSFRow firstrow = sheet.createRow(0); // 下标为0的行开始
      HSSFCell[] firstcell = new HSSFCell[CountColumnNum];
      String[] names = new String[CountColumnNum];
      names[0] = "学号";
      names[1] = "姓名";
      names[2] = "年龄";
      names[3] = "成绩";
      for (int j = 0; j < CountColumnNum; j++) {
          firstcell[j] = firstrow.createCell(j);
          firstcell[j].setCellValue(new HSSFRichTextString(names[j]));
      }
      for (int i = 0; i < xls.size(); i++) {
          // 创建一行
          HSSFRow row = sheet.createRow(i + 1);
          // 得到要插入的每一条记录
          student = xls.get(i);
          for (int colu = 0; colu <= 4; colu++) {
              // 在一行内循环
              HSSFCell no = row.createCell(0);
              no.setCellValue(student.getNo());
              HSSFCell name = row.createCell(1);
              name.setCellValue(student.getName());
              HSSFCell age = row.createCell(2);
              age.setCellValue(student.getAge());
              HSSFCell score = row.createCell(3);
              score.setCellValue(student.getScore());
          }
      }
      // 创建文件输出流，准备输出电子表格
      OutputStream out = new FileOutputStream("d:/学生记录.xls");
      hssfWorkbook.write(out);
      out.close();
      System.out.println("数据导出成功");
  }
```