hateoas | Code samples to implement HATEOAS with Spring MVC | Model View Controller library

I am reading from an external API with hypermedia links and OAuth2 authentication using Spring's WebClient. When accessing the API the JSON data is correctly converted to model objects but the supplied HAL links are either omitted if the model object extends Spring HATEOAS RepresentationModel or give a NullPointerException when the model object extends EntityModel. I suspect a problem with the hypermediaWebClientCustomizer but was not able to solve it as of now.

I tried reading the JSON with a Traverson client in a testcase. That was basically working, if i replaced relative URIs with absolute URIs and the application/json header with a application/hal+json header. I would go on with Traverson but besides these two problems Traverson requires a RestTemplate (OAuth2RestTemplate in this case), which is no longer available in our Spring version.

Any ideas if there is a problem with the configuration or what else could go wrong?

This is my configuration:

dependencies (in part)

I'm learning Spring Boot. I already declare hateoas dependency and build it successfully. (I use Gradle). But I still can't import EntityModel. What is wrong?

We have an existing application which is working fine with the SpringBoot 2.2.2.RELEASE. Now we tried to upgrade it to the SpringBoot 2.4.2 version and application is not getting started and throws the following error. In the classpath I could see only one spring-webmvc-5.3.2.jar file.

Below is the pom.xml for the referance:

I am working on the spring-boot application and I created a small application for User management and have operation like get-user, create-user etc. These operations were working fine until I used HATEOAS. Now I am getting below error when hit my web-service from POSTMAN.

Erro in POSTMAN :

I think I basically understand what HATEOAS is and why you should use it. However, I have some problems with applying this to a real world scenario.

For example:

I would like to display a list of appointments in my client application. An appointment consists of a date, a location and a person. All of this information should be displayed in a table.

My API's response currently looks something like this:

I created spring-boot gradle multi-module project which consisted of 3 modules: controller, service, repository. Main file was situated in Controller-module and named MySpringBootApplication.

I could build this project (using gradle build) and could get jar-file. But after starting this jar in command line I took the next error:

I followed the Spring on Building REST tutorial using HATEOAS at: https://spring.io/guides/tutorials/rest/ and mixed it with JPA and MySQL DB (Maven). When I run the app, I can see the initial 2 tables in MySQL workbench fine (although there is a 3rd one appearing out of nowhere?). If i perform a GET /players, it works fine. When I do a POST Request (http://localhost:8080/players) in Postman with body as JSON: { "playerName":"Pedro" }, I get a 500 status and I get an error from Spring

Not enough variable values available to expand 'id'] with root cause...

I would like to achieve full CRUD operations. A lot of doubts arises here, given that playerId is autoincrement, and the parameter registrariondate is a TIMESTAMP. This is secondary, as I guess the problem comes from making use RepresentationModelAssembler in my app, but not quite sure how to handle the responses and the petitions.

Here the project structure:

Log of the error:

I was testing my Controllers with MockMvc but I needed Mockito's when method. When creating a new instance of UserDTO that extends RepresentationalModel from Spring Hateoas, it always returns :

I am using Springboot v 2.3.2.

I have different entity class say A and B. Now after performing the CRUD operations I need to return responses in HAL format. Currently I have created methods in each controller classes. But overtime I can see that these are similar in nature. Hence I am thinking of refactoring it and applying Java Generics.

Here is a code snippet. Please guide how can I make this change or there is some other better way.

In both these methods apart from type of entity everything is same.