apache/cassandra · error · IllegalArgumentException

Unsupported format " + formatString + " supported formats…

Error message

Unsupported format " + formatString + " supported formats are YAML, MINIFIED-YAML, JSON, MINIFIED-JSON

What it means

PojoToString.Format.fromString parses a user-supplied format string into the Format enum (YAML, MINIFIED-YAML, JSON, MINIFIED-JSON). Unknown strings throw this IllegalArgumentException. It is strict input validation on serialization/deserialization format selection.

Solutions

Use exactly one of: YAML, MINIFIED-YAML, JSON, MINIFIED-JSON (uppercase, with hyphen)
Normalize/trim the input before parsing (e.g. value.trim().toUpperCase(Locale.ROOT))
Check the source of the format string (config file, flag, env var) for typos or stale values
Add a fallback default format at the call site if the value is optional

Example fix

// before
PojoToString.Format f = PojoToString.Format.fromString(config.format); // "json" -> IllegalArgumentException
// after
String normalized = config.format == null ? "YAML" : config.format.trim().toUpperCase(Locale.ROOT);
PojoToString.Format f = PojoToString.Format.fromString(normalized);

Defensive patterns

Strategy: validation

Validate before calling

Set<String> allowed = Set.of("YAML","MINIFIED-YAML","JSON","MINIFIED-JSON");
if (formatString == null || !allowed.contains(formatString.trim().toUpperCase(Locale.ROOT))) throw new IllegalArgumentException("format must be one of " + allowed);

Try / catch

try { fmt = PojoToString.Format.fromString(raw); } catch (IllegalArgumentException e) { fmt = PojoToString.Format.YAML; logger.warn("bad format '{}' defaulting to YAML", raw); }

Prevention

Uppercase+trim user-supplied format strings before parsing
Expose a dropdown/whitelist of supported formats in tooling
Add a default fallback for optional format settings
Test config parsing with unknown values

When it happens

Trigger: Calling PojoToString.Format.fromString with any string other than the four supported values, e.g. "yaml" (wrong case), "JSON_PRETTY", or an empty string from an unset config option.

Common situations: Typing format values in cassandra config or CLI flags with wrong casing, copy-pasting formats from other tools (e.g. "json-pretty"), or older/newer Cassandra versions where the format list differs.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/0ed1f763fb04a068. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/utils/PojoToString.java:85

        public boolean isYaml()
        {
            return this == YAML || this == MINIFIED_YAML;
        }

        public static Format fromString(String formatString)
        {
            formatString = toUpperCaseLocalized(formatString);
            switch (formatString)
            {
                case "YAML":
                    return YAML;
                case "MINIFIED-YAML":
                    return MINIFIED_YAML;
                case "JSON":
                    return JSON;
                case "MINIFIED-JSON":
                    return MINIFIED_JSON;
                default: throw new IllegalArgumentException("Unsupported format " + formatString
                                                            + " supported formats are YAML, MINIFIED-YAML, JSON, MINIFIED-JSON");
            }
        }
    }
    private static final Set<Class<?>> ALLOWED_PRIMITIVES = ImmutableSet.of(
        String.class,
        Double.class,
        Float.class,
        Long.class,
        Integer.class,
        Short.class,
        Byte.class
    );

    private static final List<Class<?>> ALLOWED_COLLECTIONS = ImmutableList.of(
        List.class,
        Set.class
    );

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