Method getString

core/src/main/java/io/grpc/internal/JsonUtil.java:217–229

Gets a string from an object for the given key. If the key is not present, this returns null. If the value is not a String, throws an exception.

(Map<String, ?> obj, String key)

   * If the value is not a String, throws an exception.
   */
  @Nullable
  public static String getString(Map<String, ?> obj, String key) {
    assert key != null;
    if (!obj.containsKey(key)) {
      return null;
    }
    Object value = obj.get(key);
    if (!(value instanceof String)) {
      throw new ClassCastException(
          String.format("value '%s' for key '%s' in '%s' is not String", value, key, obj));
    }
    return (String) value;
  }

  /**
   * Gets a string from an object for the given key, parsed as a duration (defined by protobuf).  If