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javaspringspring-hateoas

RestTemplate not deserializing HAL content using ParameterizedTypeReference

I am trying to retrieve a collection of resources from a REST service. My code to request this collection is as follows:

public CollectionModel<EntityModel<Doctor>> getDoctors() {
    log.info("Request to get all doctor resources");
    ParameterizedTypeReference<CollectionModel<EntityModel<Doctor>>> doctorTypeReference = 
            new ParameterizedTypeReference<CollectionModel<EntityModel<Doctor>>>() {};
    CollectionModel<EntityModel<Doctor>> doctorResources = traverson
            .follow(doctorsLink)
            .toObject(doctorTypeReference);
    log.info("The received resources are: " + doctorResources);

    return doctorResources;
}

Where Doctor is just a POJO:

@Data // Lombok annotation for setters, getter, equals, ...
@Relation(value = "doctor", collectionRelation = "doctors")
public class Doctor {
    private Long id;
    private String firstName;
    private String lastNames;
    private String email;
    private String status;
    @JsonIgnore
    private Map<String, String> links;
}

And the traverson is injected with the @Autowired annotation:

@Autowired
private Traverson traverson;

Its configuration is as follows:

@Configuration
@Slf4j
public class RestConfiguration {
    @Value("${api.uri}")
    private String restUri;
    @Value("${auth.rest.username}")
    private String username;
    @Value("${auth.rest.password}")
    private String password;
    @Value("${ssl.trust-store}")
    private Resource trustStore;
    @Value("${ssl.trust-store.password}")
    private String trustStorePassword;

    @Bean
    public RestTemplateBuilder restTemplateBuilder() {
        return new RestTemplateBuilder(restTemplate -> {
            // Configure SSL to accept self-signed certificates
            SSLContext sslContext = null;
            try {
                sslContext = SSLContexts.custom()
                        .loadTrustMaterial(null, new TrustSelfSignedStrategy()).build();
            } catch (KeyManagementException | NoSuchAlgorithmException | KeyStoreException e) {
                log.error("Unexpected exception while creating SSLContext: " + e);
            }
            SSLConnectionSocketFactory socketFactory = 
                    new SSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE);
            CloseableHttpClient httpClient = HttpClients.custom()
                .setSSLSocketFactory(socketFactory)
                .build();
            HttpComponentsClientHttpRequestFactory requestFactory = 
                    new HttpComponentsClientHttpRequestFactory();
            requestFactory.setHttpClient(httpClient);
            restTemplate.setRequestFactory(requestFactory);
            // Configure basic authentication
            restTemplate.getInterceptors().add(
                    new BasicAuthenticationInterceptor(username, password));
        });
    }

    @Bean
    public Traverson traverson() {
        Traverson traverson = new Traverson(URI.create(restUri), MediaTypes.HAL_JSON);
        // Configure the RestTemplates used by the Traverson
        traverson.setRestOperations(restTemplateBuilder().build());
        return traverson;
    }
}

I am just using a self-signed SSL certificate and basic HTTP authentication.

This being said, the logged message after the getDoctors method is called is:

The received resources are: Resources { content: [], links: [] }

I have tried using the RestTemplate directly:

public CollectionModel<EntityModel<Doctor>> getDoctors() {
    log.info("Request to get all doctor resources");
    ParameterizedTypeReference<CollectionModel<EntityModel<Doctor>>> doctorTypeReference = 
            new ParameterizedTypeReference<CollectionModel<EntityModel<Doctor>>>() {};
    // builder is the @Autowired RestTemplateBuilder
    CollectionModel<EntityModel<Doctor>> doctorResources =  builder.build()
            .exchange("https://127.0.0.1:8080/guardians/api/doctors",
                HttpMethod.GET, null, doctorTypeReference).getBody();
    log.info("The received resources are: " + doctorResources);
    ResponseEntity<Object> resp = builder.build()
            .exchange("https://127.0.0.1:8080/guardians/api/doctors",
                HttpMethod.GET, null, Object.class);
    log.info("The resources using rest template are: " + resp);

    return doctorResources;
}

Using the ParameterizedTypeReference as the response type, the received collection is still empty. However, using Object.class as the response type, the ResponseEntity body actually contains the expected information:

The resources using rest template are: <200,{_embedded={doctors=[{id=1, firstName=1, lastNames=1, email=1@guardians.com, status=AVAILABLE, absence=null, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/1}, doctors={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, shiftConfig={href=https://127.0.0.1:8080/guardians/api/doctors/shift-configs/1}, updateDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/1}}}, {id=2, firstName=2, lastNames=2, email=2@guardians.com, status=AVAILABLE, absence=null, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/2}, doctors={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, shiftConfig={href=https://127.0.0.1:8080/guardians/api/doctors/shift-configs/2}, updateDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/2}}}, {id=3, firstName=3, lastNames=3, email=3@guardians.com, status=AVAILABLE, absence=null, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/3}, doctors={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, shiftConfig={href=https://127.0.0.1:8080/guardians/api/doctors/shift-configs/3}, updateDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/3}}}, {id=4, firstName=4, lastNames=4, email=4@guardians.com, status=AVAILABLE, absence=null, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/4}, doctors={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, shiftConfig={href=https://127.0.0.1:8080/guardians/api/doctors/shift-configs/4}, updateDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/4}}},..., {id=22, firstName=22, lastNames=22, email=22@guardians.com, status=AVAILABLE, absence=null, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/22}, doctors={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, shiftConfig={href=https://127.0.0.1:8080/guardians/api/doctors/shift-configs/22}, updateDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/22}}}]}, _links={self={href=https://127.0.0.1:8080/guardians/api/doctors/{?email}, templated=true}, newDoctor={href=https://127.0.0.1:8080/guardians/api/doctors/?startDate={startDate}, templated=true}, root={href=https://127.0.0.1:8080/guardians/api/}}},[Set-Cookie:"JSESSIONID=6F797BDA2827ACD4590708F5E354122A; Path=/guardians/api; Secure; HttpOnly", X-Content-Type-Options:"nosniff", X-XSS-Protection:"1; mode=block", Cache-Control:"no-cache, no-store, max-age=0, must-revalidate", Pragma:"no-cache", Expires:"0", Strict-Transport-Security:"max-age=31536000 ; includeSubDomains", X-Frame-Options:"DENY", Content-Type:"application/json", Transfer-Encoding:"chunked", Date:"Tue, 09 Jun 2020 11:21:01 GMT", Keep-Alive:"timeout=60", Connection:"keep-alive"]>

Then, if I just request a single resource:

public EntityModel<Doctor> getDoctor(Long doctorId) {
    log.info("Request to get doctor " + doctorId);
    ParameterizedTypeReference<EntityModel<Doctor>> doctorTypeReference = 
            new ParameterizedTypeReference<EntityModel<Doctor>>() {};
    EntityModel<Doctor> doctorEntity;
    try {
        doctorEntity = traverson
                .follow(Hop.rel(doctorLink).withParameter("doctorId", doctorId))
                .toObject(doctorTypeReference);
    } catch (NotFound e) {
        log.info("The doctor was not found");
        throw e;
    }
    log.info("The received resource is: " + doctorEntity);
    return doctorEntity;
}

The content is deserialized correclty, but the links are not:

The received resource is: Resource { content: Doctor(id=1, firstName=1, lastNames=1, email=1@guardians.com, status=AVAILABLE, links=null), links: [] }

Edit

I am using the Spring framework to serve a web application. This application consumes the REST service using Spring-Hateoas.

Solution

  • I found the problem: I was not configuring the message converters of the RestTemplate to use HAL.

    To fix it, I just added the following at the end of the configuration of the RestTemplate:

    restTemplate.setMessageConverters(
    Traverson.getDefaultMessageConverters(MediaTypes.HAL_JSON));

    Now, the Bean that provides the RestTemplateBuilder looks like this:

    @Bean
public RestTemplateBuilder restTemplateBuilder() {
    return new RestTemplateBuilder(restTemplate -> {
        // Configure SSL to accept self-signed certificates
        SSLContext sslContext = null;
        try {
            sslContext = SSLContexts.custom()
                    .loadTrustMaterial(null, new TrustSelfSignedStrategy()).build();
        } catch (KeyManagementException | NoSuchAlgorithmException | KeyStoreException e) {
            log.error("Unexpected exception while creating SSLContext: " + e);
        }
        SSLConnectionSocketFactory socketFactory = 
                new SSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE);
        CloseableHttpClient httpClient = HttpClients.custom()
            .setSSLSocketFactory(socketFactory)
            .build();
        HttpComponentsClientHttpRequestFactory requestFactory = 
                new HttpComponentsClientHttpRequestFactory();
        requestFactory.setHttpClient(httpClient);
        restTemplate.setRequestFactory(requestFactory);
        // Configure basic authentication
        restTemplate.getInterceptors().add(
                new BasicAuthenticationInterceptor(username, password));
        // Configure the restTemplate to use the default HAL message converter
        restTemplate.setMessageConverters(
                Traverson.getDefaultMessageConverters(MediaTypes.HAL_JSON));
    });
}