`Converter`支持null转换 [Issue #1776]

src/main/java/com/alibaba/excel/converters/NullableObjectConverter.java

@@ -0,0 +1,10 @@
+package com.alibaba.excel.converters;
+
+/**
+ * When implementing <code>convertToExcelData</code> method, pay attention to the reference <code>value</code> may be
+ * null
+ *
+ * @author JiaJu Zhuang
+ **/
+public interface NullableObjectConverter<T> extends Converter<T> {
+}

src/main/java/com/alibaba/excel/write/executor/AbstractExcelWriteExecutor.java

@@ -3,6 +3,7 @@ package com.alibaba.excel.write.executor;
 import com.alibaba.excel.context.WriteContext;
 import com.alibaba.excel.converters.Converter;
 import com.alibaba.excel.converters.ConverterKeyBuild;
+import com.alibaba.excel.converters.NullableObjectConverter;
 import com.alibaba.excel.enums.CellDataTypeEnum;
 import com.alibaba.excel.exception.ExcelDataConvertException;
 import com.alibaba.excel.metadata.CellData;
@@ -33,10 +34,9 @@ public abstract class AbstractExcelWriteExecutor implements ExcelWriteExecutor {
     protected CellData<?> converterAndSet(WriteHolder currentWriteHolder, Class<?> clazz, CellDataTypeEnum targetType,
         Cell cell, Object value,
         ExcelContentProperty excelContentProperty, Head head, Integer relativeRowIndex) {
-        if (value == null) {
-            return new CellData<>(CellDataTypeEnum.EMPTY);
-        }
-        if (value instanceof String && currentWriteHolder.globalConfiguration().getAutoTrim()) {
+        boolean needTrim = value != null && (value instanceof String && currentWriteHolder.globalConfiguration()
+            .getAutoTrim());
+        if (needTrim) {
             value = ((String)value).trim();
         }
         CellData<?> cellData = convert(currentWriteHolder, clazz, targetType, cell, value, excelContentProperty);
@@ -75,9 +75,6 @@ public abstract class AbstractExcelWriteExecutor implements ExcelWriteExecutor {
     protected CellData<?> convert(WriteHolder currentWriteHolder, Class<?> clazz, CellDataTypeEnum targetType,
         Cell cell,
         Object value, ExcelContentProperty excelContentProperty) {
-        if (value == null) {
-            return new CellData<>(CellDataTypeEnum.EMPTY);
-        }
         // This means that the user has defined the data.
         if (value instanceof CellData) {
             CellData<?> cellDataValue = (CellData<?>)value;
@@ -115,6 +112,9 @@ public abstract class AbstractExcelWriteExecutor implements ExcelWriteExecutor {
                 new CellData<>(CellDataTypeEnum.EMPTY), excelContentProperty,
                 "Can not find 'Converter' support class " + clazz.getSimpleName() + ".");
         }
+        if (value == null && !(converter instanceof NullableObjectConverter)) {
+            return new CellData<>(CellDataTypeEnum.EMPTY);
+        }
         CellData<?> cellData;
         try {
             cellData = converter.convertToExcelData(value, excelContentProperty, currentWriteHolder);

update.md

@@ -40,6 +40,8 @@
 * 修复填充的时候，最后一行中间有空行会创建失败的bug
 * 修复`includeColumnIndexes`不包含第列 会无法导出数据的bug [Issue #1346](https://github.com/alibaba/easyexcel/issues/1346)
 * 修复`@NumberFormat`注解转换double时可能会丢失精度 [Issue #1306](https://github.com/alibaba/easyexcel/issues/1306)
+* `Converter`支持null转换 [Issue #1776](https://github.com/alibaba/easyexcel/issues/1776)
+
 
 # 2.2.3
 * 修改填充数据空数据的bug  [Issue #1274](https://github.com/alibaba/easyexcel/issues/1274)