Nrthugu

Situation

I am using SpringBoot application with the Thymeleaf templating engine. I posted a simplified version of the code that is being involved. A controller is adding an attribute to the Model object and then returning DeferredResult. At the end the attributes form the model are used in the Thymeleaf template to render them on the page.

Problem

I know if the object would not be added to the model it would throw an exception in the Thymeleaf template, because of the missing guard block or th:if. But I am setting initialized object before any code is being executed. I am also logging the value of the model for debugging purposes and its always present after the calculation. So model with appropriate key is set but at the point of rendering thymeleaf the key in model returns null value. This only happens under a heavy load. In the production system or when simulating load with more than 30 concurrent requests.

It happens 1~2 times in a 100 requests.

I store multiple objects, in the model. They are randomly null.

I also tried logging all the values with following code. All other data seems to be fine and present, only single object in the case below missing one is "model_key".

<table id="model-attributes">

  <tr th:each="var : ${#vars}">

    <td th:text="${var.key}"></td>

    <td th:text="${var.value}"></td>

  </tr>

</table>

Question

Did anyone else experienced similar issues. Can it be the Thymeleaf caching issue?

Code

Controller

@GetMapping(value = "/path") 

public DeferredResult<String> processRequest(Model model) throws Exception {



  // To make sure the model is not null add it already before any computation

  model.addAttribute("model_key", new ModelValue());

  ModelValue modelValue = calculateModel();



  // For debugging purposes

  log("Model Value " + modelValue);



  // Add the actual model

  if(modelValue != null) {

    model.addAttribute("model_key", modelValue);

  } else {

    log.error("Model was empty");

  }

  deferredResult.setResult("template_name");

}

Thymeleaf template

<p th:text="${model_key.id}">

Exception log

2018-11-12T07:45:28.691Z ERROR org.apache.catalina.core.ContainerBase.[Tomcat].[localhost].[/].[dispatcherServlet] [http-nio-8080-exec-6] : Servlet.service() for servlet dispatcherServlet threw exception

org.springframework.expression.spel.SpelEvaluationException: EL1007E: Property or field 'id' cannot be found on null    

at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:220)

org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:94)