public static JsonGenerator jsonGenerator(OutputStream stream) {
    try {
      return JSON_FACTORY.createGenerator(stream);
    } catch (IOException e) {
      throw new AssertionError("Could not create JSON generator for a memory stream.", e);
    }
  }
JSON serialization utilities and parsing code.
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/internal/JsonSerializers.java