What causes "Cannot parse ${value}; at path ${in.getPreviousPath()}" in google/gson?

Switch to ToNumberPolicy.LAZILY_PARSED_NUMBER which defers parsing and avoids the Double.valueOf path

google/gson · error · JsonParseException

Cannot parse ; at path

Error message

Cannot parse ${value}; at path ${in.getPreviousPath()}

What it means

Thrown by LONG_OR_DOUBLE.parseAsDouble() when Double.valueOf(value) raises NumberFormatException for a JSON number string. JsonReader pre-validates number syntax, so this only occurs for unusual token forms that slip through the lexer but are rejected by Double.valueOf. The message includes the value and JSON path.

Solutions

Switch to ToNumberPolicy.LAZILY_PARSED_NUMBER which defers parsing and avoids the Double.valueOf path
Switch to ToNumberPolicy.DOUBLE which uses JsonReader.nextDouble() (validated at the reader level)
Investigate and fix the malformed numeric token at the source

Example fix

// before
gsonBuilder.setNumberToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE);

// after
gsonBuilder.setNumberToNumberStrategy(ToNumberPolicy.LAZILY_PARSED_NUMBER);

Defensive patterns

Strategy: fallback

Validate before calling

// Pre-validate numeric tokens if using LONG_OR_DOUBLE with a custom source
String numStr = extractNumber(json, path);
try {
  Double.valueOf(numStr);
} catch (NumberFormatException e) {
  // fall back: treat as string or skip
  return null;
}

Try / catch

try {
  return gson.fromJson(json, type);
} catch (JsonParseException e) {
  if (e.getMessage().startsWith("Cannot parse")) {
    // retry with a more lenient number strategy
    Gson fallback = new GsonBuilder()
      .setObjectToNumberStrategy(ToNumberPolicy.LAZILY_PARSED_NUMBER)
      .create();
    return fallback.fromJson(json, type);
  }
  throw e;
}

Prevention

Prefer ToNumberPolicy.LAZILY_PARSED_NUMBER or DOUBLE over LONG_OR_DOUBLE unless you need Long/Double dispatching
If you control the producer, ensure number tokens are valid Double literals
Wrap deserialization in a fallback that switches number strategy on failure

When it happens

Trigger: Deserializing numbers with ToNumberPolicy.LONG_OR_DOUBLE configured; a JSON numeric token accepted by JsonReader's lexer but not parseable by Double.valueOf (e.g. edge cases in exponent notation, custom JsonReader subclasses emitting non-standard tokens).

Common situations: Rare under normal JsonReader usage; occurs with custom JsonReader implementations, malformed streams from non-standard producers, or version differences in number lexing.

Related errors

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/a54ff892d6658840. Report an issue: GitHub.

Appendix: source

Thrown at gson/src/main/java/com/google/gson/ToNumberPolicy.java:93

      } else {
        try {
          return Long.parseLong(value);
        } catch (NumberFormatException e) {
          return parseAsDouble(value, in);
        }
      }
    }

    private Number parseAsDouble(String value, JsonReader in) throws IOException {
      try {
        Double d = Double.valueOf(value);
        if ((d.isInfinite() || d.isNaN()) && !in.isLenient()) {
          throw new MalformedJsonException(
              "JSON forbids NaN and infinities: " + d + "; at path " + in.getPreviousPath());
        }
        return d;
      } catch (NumberFormatException e) {
        throw new JsonParseException(
            "Cannot parse " + value + "; at path " + in.getPreviousPath(), e);
      }
    }
  },

  /**
   * Using this policy will ensure that numbers will be read as numbers of arbitrary length using
   * {@link BigDecimal}.
   */
  BIG_DECIMAL {
    @Override
    public BigDecimal readNumber(JsonReader in) throws IOException {
      String value = in.nextString();
      try {
        return NumberLimits.parseBigDecimal(value);
      } catch (NumberFormatException e) {
        throw new JsonParseException(
            "Cannot parse " + value + "; at path " + in.getPreviousPath(), e);

View on GitHub (pinned to 310ac341f2)