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Fesod version

1.3.0

JDK version

17

Operating system

macOS 14.6

Steps To Reproduce

ExcelWriter writerA = FesodSheet
        .write(new File(TestFileUtil.getPath() + "first.xlsx"), TestData.class)
        .registerConverter(new ConverterA())
        .build()
        .finish();

ExcelWriter writerB = FesodSheet
        .write(new File(TestFileUtil.getPath() + "second.xlsx"), TestData.class)
        .build();

boolean hasCustomConverter = writerB.writeContext()
        .currentWriteHolder()
        .converterMap()
        .values()
        .stream()
        .anyMatch(c -> c instanceof ConverterA);

writerB.finish();

assertFalse(hasCustomConverter, "Unregistered writer inherited converter from previous writer");

Current Behavior

Converters registered in one ExcelWriter leak to other ExcelWriter instances, even when the second writer doesn't register any custom converters.

Expected Behavior

Each ExcelWriter instance should have isolated converters. The second writer should only have default converters, not custom converters from the first writer.

Anything else?

Root cause

DefaultConverterLoader returns a direct reference to a static mutable map.

This shared reference gets mutated by AbstractWriteHolder when custom converters are registered, affecting all ExcelWriter instances.

Proposed fix

Fixing AbstractWriteHolder would address the symptom, but DefaultConverterLoader should return safe copies to prevent this class of bugs wherever the API is called.

1. Make static maps immutable

private static final Map<ConverterKey, Converter<?>> defaultWriteConverter;

static {
    Map<ConverterKey, Converter<?>> map = new HashMap<>();
    // ... 
    defaultWriteConverter = Collections.unmodifiableMap(map);
}

2. Return defensive copies:

public static Map<ConverterKey, Converter<?>> loadDefaultWriteConverter() {
    return new HashMap<>(defaultWriteConverter);
}

Same issue exists in AbstractReadHolder.

Are you willing to submit a PR?

• I'm willing to submit a PR!