google/gson · error · JsonSyntaxException

Lossy conversion from

Error message

Lossy conversion from ${intValue} to short; at path ${path}

What it means

The SHORT adapter reads a JSON number as an int and rejects values outside [-32768, 65535] (the extended upper bound supports unsigned short values). Values outside this range would lose data when cast to short, so Gson throws JsonSyntaxException.

Solutions

Change the field type from short/Short to int/Integer to accommodate the value range
Pre-validate the numeric range of the JSON value before deserializing
Register a custom TypeAdapter that clamps or rejects out-of-range values

Example fix

// before
class Server { short port; } // max 65535
gson.fromJson("{\"port\":70000}", Server.class); // throws

// after
class Server { int port; }

Defensive patterns

Strategy: validation

Validate before calling

// Validate numeric range before deserializing into a short field
public static boolean isValidShort(int value) {
    return value >= Short.MIN_VALUE && value <= 65535;
}
// Usage: check before calling fromJson, or model the field as int instead

Try / catch

try {
    Server s = gson.fromJson(json, Server.class);
} catch (JsonSyntaxException e) {
    if (e.getMessage().contains("Lossy conversion") && e.getMessage().contains("short")) {
        // widen the field type to int
    }
}

Prevention

Model fields as int when the value range may exceed [-32768, 65535]
Validate numeric ranges at the API boundary before deserialization
Review short fields in DTOs for potential overflow from external data

When it happens

Trigger: Deserializing a JSON number like 70000 or -40000 into a short or Short field.

Common situations: A port number or counter field modeled as short that exceeds 65535; an API field whose value range grew beyond short capacity over time.

Related errors

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/16ab33d758468494. Report an issue: GitHub.

Appendix: source

Thrown at gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java:244

  public static final TypeAdapter<Number> SHORT =
      new TypeAdapter<Number>() {
        @Override
        public Number read(JsonReader in) throws IOException {
          if (in.peek() == JsonToken.NULL) {
            in.nextNull();
            return null;
          }

          int intValue;
          try {
            intValue = in.nextInt();
          } catch (NumberFormatException e) {
            throw new JsonSyntaxException(e);
          }
          // Allow up to 65535 to support unsigned values
          if (intValue > 65535 || intValue < Short.MIN_VALUE) {
            throw new JsonSyntaxException(
                "Lossy conversion from " + intValue + " to short; at path " + in.getPreviousPath());
          }
          return (short) intValue;
        }

        @Override
        public void write(JsonWriter out, Number value) throws IOException {
          if (value == null) {
            out.nullValue();
          } else {
            out.value(value.shortValue());
          }
        }
      };

  public static final TypeAdapterFactory SHORT_FACTORY =
      newFactory(short.class, Short.class, SHORT);

View on GitHub (pinned to 310ac341f2)