google/gson · error · IllegalStateException

Not a JSON Primitive: {this}

Error message

Not a JSON Primitive: {this}

What it means

Thrown by JsonElement.getAsJsonPrimitive() when the element is not a JsonPrimitive (e.g. it is an object, array, or null). Used when the caller wants the primitive holder to then extract a typed scalar.

Source

Thrown at gson/src/main/java/com/google/gson/JsonElement.java:194

      return (JsonArray) this;
    }
    throw new IllegalStateException("Not a JSON Array: " + this);
  }

  /**
   * Convenience method to get this element as a {@link JsonPrimitive}. If this element is of some
   * other type, an {@link IllegalStateException} will result. Hence it is best to use this method
   * after ensuring that this element is of the desired type by calling {@link #isJsonPrimitive()}
   * first.
   *
   * @return this element as a {@link JsonPrimitive}.
   * @throws IllegalStateException if this element is of another type.
   */
  public JsonPrimitive getAsJsonPrimitive() {
    if (isJsonPrimitive()) {
      return (JsonPrimitive) this;
    }
    throw new IllegalStateException("Not a JSON Primitive: " + this);
  }

  /**
   * Convenience method to get this element as a {@link JsonNull}. If this element is of some other
   * type, an {@link IllegalStateException} will result. Hence it is best to use this method after
   * ensuring that this element is of the desired type by calling {@link #isJsonNull()} first.
   *
   * @return this element as a {@link JsonNull}.
   * @throws IllegalStateException if this element is of another type.
   * @since 1.2
   */
  @CanIgnoreReturnValue // When this method is used only to verify that the value is JsonNull
  public JsonNull getAsJsonNull() {
    if (isJsonNull()) {
      return (JsonNull) this;
    }
    throw new IllegalStateException("Not a JSON Null: " + this);
  }

View on GitHub (pinned to 8b8628c656)

Solutions

1. Guard with element.isJsonPrimitive() first.
2. Handle isJsonNull() for nullable scalar fields.
3. Branch on isJsonObject()/isJsonArray() if the field is polymorphic.

Example fix

// before
JsonPrimitive p = el.getAsJsonPrimitive();
// after
if (el.isJsonPrimitive()) {
  JsonPrimitive p = el.getAsJsonPrimitive();
} else if (el.isJsonNull()) {
  // null scalar
}

if (!element.isJsonPrimitive()) {
  throw new IllegalStateException("expected JSON primitive, got " + element.getClass().getSimpleName());
}
JsonPrimitive p = element.getAsJsonPrimitive();

boolean isPrimitiveValue(JsonElement e) { return e != null && e.isJsonPrimitive(); }

try {
  JsonPrimitive p = el.getAsJsonPrimitive();
} catch (IllegalStateException e) {
  // default / skip non-primitive value
}

When it happens

Trigger: Calling element.getAsJsonPrimitive() on a JsonObject, JsonArray, or JsonNull.

Common situations: Iterating map values and assuming all are scalars; a field that is sometimes null; a nested object where a primitive was expected.

Related errors

• Not a JSON Object: {this}
• Not a JSON Array: {this}
• Array must have size 1, but has size {size}
• Not a JSON Null: {this}
• {getClass().getSimpleName()}

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/0138dbbe6cd53cc6.json. Report an issue: GitHub.