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Converter

This chapter introduces how to use custom converters when writing data.

Overview​

Fesod supports custom data converters for write operations. You can transform Java field values before they are written to Excel cells, enabling custom formatting, encryption, or any data transformation logic.

Per-Field Converter​

Overview​

Apply a converter to a specific field using the @ExcelProperty(converter = ...) annotation.

Converter​

public class CustomStringStringConverter implements Converter<String> {
    @Override
    public Class<?> supportJavaTypeKey() {
        return String.class;
    }

    @Override
    public CellDataTypeEnum supportExcelTypeKey() {
        return CellDataTypeEnum.STRING;
    }

    @Override
    public String convertToJavaData(ReadConverterContext<?> context) {
        return "Custom: " + context.getReadCellData().getStringValue();
    }

    @Override
    public WriteCellData<?> convertToExcelData(WriteConverterContext<String> context) {
        return new WriteCellData<>("Custom: " + context.getValue());
    }
}

POJO Class​

@Getter
@Setter
@EqualsAndHashCode
public class ConverterData {
    @ExcelProperty(value = "String Title", converter = CustomStringStringConverter.class)
    private String string;

    @DateTimeFormat("yyyy-MM-dd HH:mm:ss")
    @ExcelProperty("Date Title")
    private Date date;

    @NumberFormat("#.##%")
    @ExcelProperty("Number Title")
    private Double doubleData;
}

Code Example​

@Test
public void converterWrite() {
    String fileName = "converterWrite" + System.currentTimeMillis() + ".xlsx";
    FesodSheet.write(fileName, ConverterData.class)
        .sheet()
        .doWrite(data());
}

Global Converter Registration​

Overview​

Register a converter at the builder level to apply it to ALL fields matching the Java type and Excel type. This is useful when you want the same transformation applied globally without annotating each field.

Code Example​

@Test
public void globalConverterWrite() {
    String fileName = "globalConverterWrite" + System.currentTimeMillis() + ".xlsx";
    FesodSheet.write(fileName, DemoData.class)
        .registerConverter(new CustomStringStringConverter())
        .sheet()
        .doWrite(data());
}

Converter Resolution Priority​

When multiple converters could apply to a field, Fesod resolves them in this order:

  1. Field-level converter (@ExcelProperty(converter = ...)) — highest priority
  2. Builder-level converter (.registerConverter(...))
  3. Built-in default converter — lowest priority