grpc/grpc-java · error · IllegalArgumentException

value '%s' for key '%s' in '%s' is not a number

Error message

value '%s' for key '%s' in '%s' is not a number

What it means

JsonUtil.getNumberAsDouble requires the JSON value to be a number (or a numeric string). When the value is neither — an object, array, or boolean — it throws IllegalArgumentException('value ... is not a number'), including the value, key, and parent object in the message.

Source

Thrown at core/src/main/java/io/grpc/internal/JsonUtil.java:120

  @Nullable
  public static Double getNumberAsDouble(Map<String, ?> obj, String key) {
    assert key != null;
    if (!obj.containsKey(key)) {
      return null;
    }
    Object value = obj.get(key);
    if (value instanceof Double) {
      return (Double) value;
    }
    if (value instanceof String) {
      try {
        return Double.parseDouble((String) value);
      } catch (NumberFormatException e) {
        throw new IllegalArgumentException(
            String.format("value '%s' for key '%s' is not a double", value, key));
      }
    }
    throw new IllegalArgumentException(
        String.format("value '%s' for key '%s' in '%s' is not a number", value, key, obj));
  }

  /**
   * Gets a number from an object for the given key, casted to an integer.  If the key is not
   * present, this returns null.  If the value does not represent an integer, throws an exception.
   */
  @Nullable
  public static Integer getNumberAsInteger(Map<String, ?> obj, String key) {
    assert key != null;
    if (!obj.containsKey(key)) {
      return null;
    }
    Object value = obj.get(key);
    if (value instanceof Double) {
      Double d = (Double) value;
      int i = d.intValue();
      if (i != d) {

View on GitHub (pinned to 64daddc1f3)

Solutions

  1. Fix the JSON so the key maps to a plain number (or numeric string)
  2. Cross-check the field against the gRPC service config / xDS schema documentation
  3. Check the parent object printed in the message to find which fragment introduced the wrong type
  4. Pin and update the config-generating tool so it emits the documented types

Example fix

// before
{"timeoutSeconds": {"value": 30}}
// after
{"timeoutSeconds": 30}
Defensive patterns

Strategy: validation

Validate before calling

Object v = cfg.get("timeoutSeconds");
if (v != null && !(v instanceof Number) && !(v instanceof String)) throw new IllegalArgumentException("timeoutSeconds must be a number");

Type guard

boolean isNumberLike(Object v) { return v instanceof Number || v instanceof String; }

Try / catch

try { double d = JsonUtil.getNumberAsDouble(cfg, "timeoutSeconds"); }
catch (IllegalArgumentException e) { if (e.getMessage().contains("is not a number")) { log.error("wrong JSON type: {}", e.getMessage()); } throw e; }

Prevention

When it happens

Trigger: A config key expected to be numeric holds a structured JSON value — e.g. writing an object/array where a number is required in service config or xDS bootstrap fields like timeout or percentage.

Common situations: Schema misunderstanding: author nests extra fields under the numeric key; generator bug emitting a wrong JSON type; merging config fragments so an object overwrites a scalar.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of grpc/grpc-java@64daddc1f3 (2026-09-08). Data as JSON: /api/errors/630315dc709329d6. Report an issue: GitHub.