chinabugotech/hutool · error · UnsupportedOperationException

Unsupported toMap value type: {}

Error message

Unsupported toMap value type: {}

What it means

MapConverter.convertInternal accepts a Map or a readable Bean (BeanUtil.isReadableBean). Any other source type (primitive, scalar String that is not a bean, array, etc.) reaches the else branch and throws UnsupportedOperationException naming the value class.

Source

Thrown at hutool-core/src/main/java/cn/hutool/core/convert/impl/MapConverter.java:86

			final Class<?> mapClass = TypeUtil.getClass(this.mapType);
			if (null == mapClass || mapClass.isAssignableFrom(AbstractMap.class)) {
				// issue#I6YN2A，默认有序
				map =  new LinkedHashMap<>();
			} else{
				map = MapUtil.createMap(mapClass);
			}
			convertMapToMap((Map) value, map);
		} else if (BeanUtil.isReadableBean(value.getClass())) {
			if(value.getClass().getName().equals("cn.hutool.json.JSONArray")){
				// issue#3795 增加JSONArray转Map错误检查
				throw new UnsupportedOperationException(StrUtil.format("Unsupported {} to Map.", value.getClass().getName()));
			}

			map = BeanUtil.beanToMap(value);
			// 二次转换，转换键值类型
			map = convertInternal(map);
		} else {
			throw new UnsupportedOperationException(StrUtil.format("Unsupported toMap value type: {}", value.getClass().getName()));
		}
		return map;
	}

	/**
	 * Map转Map
	 *
	 * @param srcMap 源Map
	 * @param targetMap 目标Map
	 */
	private void convertMapToMap(Map<?, ?> srcMap, Map<Object, Object> targetMap) {
		final ConverterRegistry convert = ConverterRegistry.getInstance();
		srcMap.forEach((key, value)->{
			key = TypeUtil.isUnknown(this.keyType) ? key : convert.convert(this.keyType, key);
			value = TypeUtil.isUnknown(this.valueType) ? value : convert.convert(this.valueType, value);
			targetMap.put(key, value);
		});
	}

View on GitHub (pinned to 8870454b2a)

Solutions

1. Wrap the scalar in a Map before converting.
2. Use the correct target type for the source (e.g. String -> String, Number -> Number).
3. Pre-check whether the source is a Map or a readable bean before targeting Map.

Example fix

// before
Map m = Convert.convert("hello", Map.class);

// after - wrap structured
Map<String,Object> src = Collections.singletonMap("value", "hello");
Map m = Convert.convert(src, Map.class);

if (!(value instanceof Map) && !BeanUtil.isReadableBean(value.getClass())) {
    value = Collections.singletonMap("value", value); // or pick a different target
}
Convert.convert(value, Map.class);

value instanceof Map || BeanUtil.isReadableBean(value.getClass())

try {
    return Convert.convert(value, Map.class);
} catch (UnsupportedOperationException e) {
    if (e.getMessage().startsWith("Unsupported toMap value type")) { /* wrap scalar in a Map */ }
    else throw e;
}

When it happens

Trigger: Calling Convert.convert(scalar, Map.class) where scalar is a Number, Boolean, plain String, primitive array, etc.

Common situations: Misrouting a scalar through Map conversion; generic pipeline that assumes every value is bean-shaped.

Related errors

• Unsupported to map from [{}] of type: {}
• Unsupported {} to Map.
• Unsupported to map from [{}] of type: {}
• Default value [{}]({}) is not the instance of [{}]
• Unsupported source type: {}

AI-assisted analysis of chinabugotech/hutool@8870454b2a (2026-08-14). Data as JSON: /api/errors/cf91946d1b755cc8. Report an issue: GitHub.