EasyExcel自定义Converter全局加载器以及加载Converter

说明：该文章是转载大牛的文章；尊重版权，原链接为：https://blog.youkuaiyun.com/fsadkjl/article/details/105823830

EasyExcel自定义Converter全局加载器以及加载Converter

本篇文章主要讲以下问题：

1.converter三种加载方式以及注意事项
2.EasyExcel的converter加载流程
3.自定义全局加载器converterLoader

converter三种加载方式以及注意事项

- 在需要转换的字段上的@ExcelProperty注解上添加converter属性

@ExcelProperty(value = "创建时间", index = 3, converter = LocalDateTimeConverter.class)
private LocalDateTime createTime;

• 优点：此种方式只需在每个需要转换的字段上添加converter即可

• 缺点：如果有很多类，每个类中有很多需要单独转换的字段要写很多次就尴尬了！

• 适用场景：任何场景

• 在创建ExcelWriterBuilder时候为这次操作单独加载转换器

EasyExcel.write(response.getOutputStream(), UserExport.class).registerConverter(new LocalDateTimeConverter()).sheet("test").doWrite(list);

• 优点：此种方式只要在每个导入导出的方法上都单独加载转换器，不用在每个需要转换的字段上都添加converter了，一定程度上可以减少我们的工作量
• 缺点：只在本方法中有效，其他方法无效，如果有很多不同的导入导出方法就又尴尬了！
• 适用场景：适用于LocalDateTimeConverter场景，但是如果要是SexConverter场景就不适合！因为前者是LocalDateTime与String之间的转换，后者它的本质是Integer与String互相转换，因为String字段可以代表年龄、性别、等信息，所以没法转换，不知道我描述的是否清楚？

- 自定义全局加载器CustomerDefaultConverterLoader

@Configuration
public class CustomerDefaultConverterLoader {
	//存放写时用到的converter
	private static final String ALL_CONVERTER = "allConverter";
	//存放所有的converter
	private static final String WRITE_CONVERTER = "defaultWriteConverter";

	@Bean
	public DefaultConverterLoader init() throws IllegalAccessException {
		DefaultConverterLoader converters = new DefaultConverterLoader();
		Field[] fields = converters.getClass().getDeclaredFields();
		for (Field field : fields) {
			field.setAccessible(true);
			if (field.getType() == Map.class) {
				Map<String, Converter> oldMap = (Map<String, Converter>) field.get(converters);
				//兼容高版本（2.2.0+）通过静态代码块初始化 复用旧代码 节省空间
				if (oldMap != null && !oldMap.isEmpty()) {
					if (WRITE_CONVERTER.equalsIgnoreCase(field.getName())) {
						putWriteConverter(oldMap, new LocalDateTimeConverter());
					} else if (ALL_CONVERTER.equalsIgnoreCase(field.getName())) {
						putAllConverter(oldMap, new LocalDateTimeConverter());
					}
					field.set(converters, oldMap);
				} else {
					setConverter(converters, field);
				}
			}
		}
		return converters;
	}

	private void setConverter(DefaultConverterLoader converters, Field field) throws IllegalAccessException {
		if (WRITE_CONVERTER.equalsIgnoreCase(field.getName())) {
			Map<String, Converter> map = new HashMap<>(32);
			//我的LocalDateTimeConverter
			putWriteConverter(map, new LocalDateTimeConverter());
			//以下jar包自带的Converter
			putWriteConverter(map, new BigDecimalNumberConverter());
			putWriteConverter(map, new BooleanBooleanConverter());
			putWriteConverter(map, new ByteNumberConverter());
			putWriteConverter(map, new DateStringConverter());
			putWriteConverter(map, new DoubleNumberConverter());
			putWriteConverter(map, new FloatNumberConverter());
			putWriteConverter(map, new IntegerNumberConverter());
			putWriteConverter(map, new LongNumberConverter());
			putWriteConverter(map, new ShortNumberConverter());
			putWriteConverter(map, new StringStringConverter());
			putWriteConverter(map, new FileImageConverter());
			putWriteConverter(map, new InputStreamImageConverter());
			putWriteConverter(map, new ByteArrayImageConverter());
			putWriteConverter(map, new BoxingByteArrayImageConverter());
			putWriteConverter(map, new UrlImageConverter());
			field.set(converters, map);
		} else if (ALL_CONVERTER.equalsIgnoreCase(field.getName())) {
			Map<String, Converter> map = new HashMap<>(64);
			//我的LocalDateTimeConverter
			putAllConverter(map, new LocalDateTimeConverter());
			//以下jar包自带的Converter
			putAllConverter(map, new BigDecimalBooleanConverter());
			putAllConverter(map, new BigDecimalNumberConverter());
			putAllConverter(map, new BigDecimalStringConverter());

			putAllConverter(map, new BooleanBooleanConverter());
			putAllConverter(map, new BooleanNumberConverter());
			putAllConverter(map, new BooleanStringConverter());

			putAllConverter(map, new ByteBooleanConverter());
			putAllConverter(map, new ByteNumberConverter());
			putAllConverter(map, new ByteStringConverter());

			putAllConverter(map, new DateNumberConverter());
			putAllConverter(map, new DateStringConverter());

			putAllConverter(map, new DoubleBooleanConverter());
			putAllConverter(map, new DoubleNumberConverter());
			putAllConverter(map, new DoubleStringConverter());

			putAllConverter(map, new FloatBooleanConverter());
			putAllConverter(map, new FloatNumberConverter());
			putAllConverter(map, new FloatStringConverter());

			putAllConverter(map, new IntegerBooleanConverter());
			putAllConverter(map, new IntegerNumberConverter());
			putAllConverter(map, new IntegerStringConverter());

			putAllConverter(map, new LongBooleanConverter());
			putAllConverter(map, new LongNumberConverter());
			putAllConverter(map, new LongStringConverter());

			putAllConverter(map, new ShortBooleanConverter());
			putAllConverter(map, new ShortNumberConverter());
			putAllConverter(map, new ShortStringConverter());

			putAllConverter(map, new StringBooleanConverter());
			putAllConverter(map, new StringNumberConverter());
			putAllConverter(map, new StringStringConverter());
			putAllConverter(map, new StringErrorConverter());
			field.set(converters, map);
		}
	}

	private void putWriteConverter(Map<String, Converter> map, Converter converter) {
		map.put(ConverterKeyBuild.buildKey(converter.supportJavaTypeKey()), converter);
	}

	private void putAllConverter(Map<String, Converter> map, Converter converter) {
		map.put(ConverterKeyBuild.buildKey(converter.supportJavaTypeKey(), converter.supportExcelTypeKey()), converter);
	}
}

• 优点：此种方式可以全局配置Converter，一劳永逸！配置完之后不用再单独修改字段或者修改方法，可以理解为EasyExcel从现在支持LocalDateTime啦！
• 缺点：只能添加特殊的Converter
• 适用场景：与第二种场景一样！切记SexConverter不可放到全局加载器中，不信你试试。。。试过之后你就理解我为什么写这么多文字去介绍他们的适用场景了