如何重构此开关案例

Question

我正在尝试从excel中读取数据，并从每一列中提取数据并将其存储在另一个变量中。 每个案例代表该列。 我使用fbDataField将行数据添加到列表名称fbList中。 可以将此代码重构以使其看起来很干净吗？

for(int i=0;i< workbook.getNumberOfSheets(); i++){

    Sheet sheet = workbook.getSheetAt(i);

    Iterator<Row> rowIterator = sheet.iterator();

    while(rowIterator.hasNext()){

        FacebookFields fbDataField= new FacebookFields();
        Row row = rowIterator.next();
        if(row.getRowNum()== 0 )
        {
            continue;
        }
        Iterator<Cell> cellIterator = row.cellIterator();

        while(cellIterator.hasNext()){

            Cell cell= cellIterator.next();

            switch(cell.getColumnIndex()){
            case 0: fbDataField.setName(cell.getStringCellValue());
            break;
            case 1: fbDataField.setId(cell.getStringCellValue());
            break;
            case 2: fbDataField.setDate(cell.getStringCellValue());
            break;
            case 3: fbDataField.setMessage(cell.getStringCellValue());
            break;
            case 4: fbDataField.setType(cell.getStringCellValue());
            break;
            case 5: fbDataField.setPage(cell.getStringCellValue());
            break;
            case 6: fbDataField.setLikeCount(String.valueOf(cell.getNumericCellValue()));
            break;
            case 7: fbDataField.setCommentCount(String.valueOf(cell.getNumericCellValue()));
            break;
            case 8: fbDataField.setShareCount(String.valueOf(cell.getNumericCellValue()));
            break;

            }

        } 
        fbList.add(fbDataField);
    }
}

Answer 1

POI¹的文档指出，它具有iterator()别名来启用foreach循环²：

for (Sheet sheet : workbook) {
    for (Row row : sheet) {

        if (row.getRowNum() == 0) {
            continue;
        }

        FacebookFields record = new FacebookFields();

        for (Cell cell : row) {
            switch (cell.getColumnIndex()) {
                case 0: record.setName        (cell.getStringCellValue()); break; 
                case 1: record.setId          (cell.getStringCellValue()); break; 
                case 2: record.setDate        (cell.getStringCellValue()); break; 
                case 3: record.setMessage     (cell.getStringCellValue()); break; 
                case 4: record.setType        (cell.getStringCellValue()); break; 
                case 5: record.setPage        (cell.getStringCellValue()); break; 
                case 6: record.setLikeCount   (String.valueOf(cell.getNumericCellValue())); break; 
                case 7: record.setCommentCount(String.valueOf(cell.getNumericCellValue())); break; 
                case 8: record.setShareCount  (String.valueOf(cell.getNumericCellValue())); break; 
            }
        }

        fbList.add(record);
    }
}

注意：

1. 我考虑将数字字段的类型更改为非String
2. 我会考虑提取方法以读取一行并读取工作表：

for (Sheet sheet : workbook) {
    readSheet(sheet, fbList);
}

private static void readSheet(final Sheet sheet, final List<FacebookFields> fbList) {
    for (Row row : sheet)
        if (row.getRowNum() > 0)
            fbList.add(readRow(row));
}

private static FacebookFields readRow(final Row row) {
    FacebookFields record = new FacebookFields();

    for (Cell cell : row) {
        switch (cell.getColumnIndex()) {
            case 0: record.setName        (cell.getStringCellValue()); break; 
            case 1: record.setId          (cell.getStringCellValue()); break; 
            case 2: record.setDate        (cell.getStringCellValue()); break; 
            case 3: record.setMessage     (cell.getStringCellValue()); break; 
            case 4: record.setType        (cell.getStringCellValue()); break; 
            case 5: record.setPage        (cell.getStringCellValue()); break; 
            case 6: record.setLikeCount   (cell.getNumericCellValue()); break; 
            case 7: record.setCommentCount(cell.getNumericCellValue()); break; 
            case 8: record.setShareCount  (cell.getNumericCellValue()); break; 
        }
    }

    return record;
}

---

¹例如https://poi.apache.org/apidocs/org/apache/poi/hssf/usermodel/HSSFWorkbook.html

²Java “ for each”循环如何工作？

Answer 2

我将enum用作复制工厂。

enum CellToFb {

    Name {

                @Override
                void copy(FacebookFields fb, Cell cell) {
                    fb.setName(cell.getStringCellValue());
                }
            },
    Id {

                @Override
                void copy(FacebookFields fb, Cell cell) {
                    fb.setId(cell.getStringCellValue());
                }
            };

    // Every enum must be able to copy one cell to the correct FB field.
    public abstract void copy(FacebookFields fb, Cell cell);
}

public void test() {
    // Get all copiers - one for each column.
    CellToFb[] copiers = CellToFb.values();
    while (cellIterator.hasNext()) {
        Cell cell = cellIterator.next();
        // Call the correct copier.
        copiers[cell.getColumnIndex()].copy(fbDataField, cell);
    }
}

每个枚举都知道如何复制特定的列。 只需确保枚举与列匹配即可。 您的复制代码变得非常简单。

这项技术很好地移植到Java 8 lambda。

// Couple of simple demo classes.
class From {

    String id;
    String name;

    @Override
    public String toString() {
        return "{" + id + "," + name + "}";
    }
}

class To {

    String identifier;
    String value;

    @Override
    public String toString() {
        return "{" + identifier + "," + value + "}";
    }
}

enum FromToTo implements BiConsumer<To, From> {

    // Each field defines it's own copying lambda.
    Id((to, from) -> to.identifier = from.id),
    Value((to, from) -> to.value = from.name);
    // The copying lambda.
    private final BiConsumer<To, From> copy;

    private FromToTo(BiConsumer<To, From> copy) {
        this.copy = copy;
    }

    @Override
    public void accept(To to, From from) {
        // Delegate to the copying lambda.
        copy.accept(to, from);
    }

    // Take s static copy to avoid duplicating.
    private static final FromToTo[] copiers = FromToTo.values();

    public static void copy(To to, From from) {
        // Useful function to copy fields from -> to
        Arrays.stream(copiers)
                .forEach(ftt -> ftt.accept(to, from));
    }

}

public void test() {
    From f = new From();
    f.id = "id";
    f.name = "name";
    To t = new To();
    FromToTo.copy(t, f);
    System.out.println(f + " -> " + t);
}