bengbengbalabalabeng commented on issue #648:
URL: https://github.com/apache/fesod/issues/648#issuecomment-3468192542
问题触发条件
1. 用户通过 registerConverter() 注册了一个或多个全局自定义的 Converter<?>。
2. 在需要转换的实体类字段上，未使用 @ExcelProperty(converter = ...) 注解显式指定转换器。
3. 写入的目标文件格式不是 CSV (ExcelTypeEnum.CSV)。
初步分析
问题的根源在于 `AbstractExcelWriteExecutor#doConvert` 方法中获取全局转换器的逻辑。
`cn.idev.excel.write.metadata.holder.AbstractWriteHolder`
<details>
<summary>Code</summary>
```java
public AbstractWriteHolder(WriteBasicParameter writeBasicParameter,
AbstractWriteHolder parentAbstractWriteHolder) {
// ......
// Set converterMap
if (parentAbstractWriteHolder == null) {
setConverterMap(DefaultConverterLoader.loadDefaultWriteConverter());
} else {
setConverterMap(new
HashMap<>(parentAbstractWriteHolder.getConverterMap()));
}
if (writeBasicParameter.getCustomConverterList() != null
&& !writeBasicParameter.getCustomConverterList().isEmpty()) {
for (Converter<?> converter :
writeBasicParameter.getCustomConverterList()) {
getConverterMap()
.put(
ConverterKeyBuild.buildKey(
//
[Mark-1]
converter.supportJavaTypeKey(),
converter.supportExcelTypeKey()),
converter);
}
}
}
```
</details>
> Note: [Mark-1]
`cn.idev.excel.write.executor.AbstractExcelWriteExecutor#doConvert`
<details>
<summary>Code</summary>
```java
private WriteCellData<?> doConvert(CellWriteHandlerContext
cellWriteHandlerContext) {
ExcelContentProperty excelContentProperty =
cellWriteHandlerContext.getExcelContentProperty();
Converter<?> converter = null;
// get converter by @ExcelProperty(converter = ...)
if (excelContentProperty != null) {
converter = excelContentProperty.getConverter();
}
// get converter by Converter Map
if (converter == null) {
// csv is converted to string by default
// [Mark-2]
if (writeContext.writeWorkbookHolder().getExcelType() ==
ExcelTypeEnum.CSV) {
cellWriteHandlerContext.setTargetCellDataType(CellDataTypeEnum.STRING);
}
converter = writeContext
.currentWriteHolder()
.converterMap()
.get(ConverterKeyBuild.buildKey(
cellWriteHandlerContext.getOriginalFieldClass(),
// [Mark-3]
cellWriteHandlerContext.getTargetCellDataType()));
}
// ......
if (converter == null) {
throw new ExcelWriteDataConvertException(
cellWriteHandlerContext,
"Can not find 'Converter' support class "
+
cellWriteHandlerContext.getOriginalFieldClass().getSimpleName() + ".");
}
// ......
return cellData;
}
```
</details>
> Note: [Mark-2]、[Mark-3]
在 `ExcelWriteAddExecutor#add` 方法（调用链）中，会先构造一个 `CellWriteHandlerContext`
对象，但此时并没有对 `targetCellDataType` 字段进行赋值。随后调用 `converterAndSet` -> `doConvert`
时，如果 `@ExcelProperty` 注解未显式指定 `converter`，就会进入全局 `Converter<?>`的获取逻辑。
然而，当 [Mark-2] 条件不成立时，[Mark-3] 中的 `TargetCellDataType` 会一直保持为 `NULL`。这会导致通过
[Mark-1] 添加的 `Converter<?>` 无法被正确匹配，从而抛出异常。
讨论
- 是否需要在 [Mark-1] 添加 excelTypeKey（感觉
`CellWriteHandlerContext#targetCellDataType` 类型赋值问题不好解）
- 个人觉得通过 registerConverter() 同时注册多个相同类型的全局 Converter 本身不太合理，应该使用
@ExcelProperty(converter = ...) 显式指定会更好（优先级高）。
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