Spring Boot /百里香嵌套循环对象访问

Question

I am using Spring Boot and Thymeleaf to create a single landing page for my application. For this, I need to render a List of Host objects that all contain a Container. Here is the relevant code:

public class Container {
    private String name;
    private String baseUrl;
    private String status;

    public Container(String name, String baseUrl, String status) {
        this.name = name;
        this.baseUrl = baseUrl;
        this.status = status;
    }

    public String getName() { return name; }
    public String getBaseUrl() { return baseUrl; }
    public String getStatus() { return status; }
}

public class Host {
    private HashMap<String, Container> containers;
    ....
    public List<Container> getContainers() {
         return containers.values();
    }
}

@RequestMapping("/")
public class IndexController {
      @RequestMapping("/")
      public String getIndex(Model model) {
          model.addAttribute("hosts", hostRepository.getAllServers());
          return "index";
      }
}

Now I want to iterate over all servers and display the information about each Container in a table. My Thymeleaf template looks like this:

<div class="panel panel-default" th:each="host : ${hosts}">
            <div class="panel-heading">
                <b th:text="${host.name}">Host X</b>
                <div class="panel-body">
                    <table class="table">
                        <thead>
                            <tr>
                                <th>Name</th>
                                <th>URL</th>
                                <th>Status</th>
                            </tr>
                        </thead>
                        <tbody>
                            <tr th:each="container : ${host.getContainers()}">
           <!-- HERE IS THE PROBLEM -->
                                <td th:text="${container.name}">Service1</td>
                                <td th:text="${container.baseUrl}">domain.com/api/url</td>
                                <td th:text="${container.status}">RUNNING</td>
           <!-- HERE ENDS THE PROBLEM -->
                            </tr>
                        </tbody>
                    </table>
                </div>
            </div>
</div>

My problem is the part where is access the container's properties (marked by the commentary). Every time I get a SpringEL Exception. If I remove the th:text="${container.xy}" and replaces it with th:text="${container} a String version of the container is shown so I have access to the object and the loop it working properly. I also tried to replace the field access with getters (eg getStatus() ) but it also does not work.

Thanks for your help. If you need more information, feel free to ask.

Setup:

• Java 8
• Spring Boot Starter Web
• Thymeleaf

edit : The exception thrown is: nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "container.name" (index:35) where index:35 is the first problematic line.

The toString() output when using ${container} is jenkins=com.my.app.Container@7552c269 and jenkins is the name attribute of the Container instance.

Solution It seemed that the nested loop was iterating over a Map instead of a List. Changing ${container.xy} to ${container.getValue().xy} solved the problem.

Answer 1

Solution

It seemes that the nested loop was iterating over a org.thymeleaf.util.EvaluationUtil$MapEntry instead of a List. Changing ${container.xy} to ${container.getValue().xy} solved the problem.

Bits learned along the way:

• Override the toString() method to obtain formatted information about the object iterating over. In this case the output was key=value which altough value was expected. This gave a hint that the current object must be something else than a Container instance
• Look at the stack trace of Thymeleaf (usually its a hint that something is null or not public)
• Use getClass() on the current object during the iteration to check if something went wrong here