alibaba/spring-ai-alibaba · info

Unsupported charset ' ', falling back to UTF-8

Error message

Unsupported charset '{}', falling back to UTF-8

What it means

extractCharset found a charset name in the Content-Type header or HTML meta tag that Charset.forName does not recognize on this JVM; it logs the warning and returns empty, causing the tool to fall back to decoding the body as UTF-8.

Solutions

1. Usually safe to ignore: content decodes as UTF-8; check output for mojibake.
2. If decoding is wrong, pre-normalize the source page or serve it with a correct Content-Type header.
3. Ensure the JVM has the full charsets module (java.base plus jdk.charsets) if exotic encodings are needed.
4. Fix the upstream page's charset declaration if you control it.

try { Charset.forName(declared); } catch (Exception e) { /* declared charset unsupported; expect UTF-8 fallback */ }

When it happens

Trigger: A page declares a misspelled, non-standard, or platform-specific charset (e.g. 'utf8' variants, 'gb2312' aliases absent from the charset provider, garbage values) in its metadata.

Common situations: Scraping legacy Chinese/European sites declaring charsets like 'GB2312' or 'ISO-8859-1' aliases on restricted JVMs, pages with malformed meta tags, CDN-injected wrong headers.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Content too long ( characters). Truncating to characters.
• 会话 不存在，创建新会话
• Failed to parse version number
• Fallback model failed
• Fetch attempt failed for URL

AI-assisted analysis of alibaba/spring-ai-alibaba@f82da0b50f (2026-09-09). Data as JSON: /api/errors/e3000ff4fc82f7c3. Report an issue: GitHub.

Appendix: source

Thrown at spring-ai-alibaba-agent-framework/src/main/java/com/alibaba/cloud/ai/graph/agent/tools/WebFetchTool.java:361

		}
		catch (InterruptedException e) {
			Thread.currentThread().interrupt();
			throw new WebFetchException("Request was interrupted", e);
		}
	}

	private Optional<Charset> extractCharset(HttpResponse<?> response) {
		return response.headers()
			.firstValue("Content-Type")
			.flatMap(contentType -> {
				Matcher matcher = CHARSET_PATTERN.matcher(contentType);
				if (matcher.find()) {
					String charsetName = matcher.group(1);
					try {
						return Optional.of(Charset.forName(charsetName));
					}
					catch (Exception e) {
						logger.warn("Unsupported charset '{}', falling back to UTF-8", charsetName);
						return Optional.empty();
					}
				}
				return Optional.empty();
			});
	}

	private String summarize(String content, String userQuery) {
		try {
			String response = this.chatClient.prompt()
				.user(u -> u.text(FETCH_SUMMARIZE_PROMPT).param("content", content).param("userQuery", userQuery))
				.call()
				.content();
			return response != null ? response : "Error: Received empty response from AI model";
		}
		catch (Exception e) {
			logger.error("Failed to summarize content", e);
			return "Error summarizing content: " + e.getMessage();

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