How to register Jackson2HalModule manually for standalone unit testing?

Question

I tried:

@BeforeClass
public static void setUpClass() {
    CurieProvider curieProvider = new DefaultCurieProvider("a", new UriTemplate("a{yey}"));
    RelProvider relProvider = new DefaultRelProvider();
    ObjectMapper halObjectMapper = JsonUtils.mapper; 
    halObjectMapper.registerModule(new Jackson2HalModule());
    halObjectMapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider));
}

but still got error:

03:26:25.936 [main] ERROR org.soluvas.json.JsonUtils - Cannot serialize id.co.bippo.product.rs.commerceplug.ProductOrServiceImpl as JSON
com.fasterxml.jackson.databind.JsonMappingException: Class org.springframework.hateoas.hal.Jackson2HalModule$HalLinkListSerializer has no default (no arg) constructor
    at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1042) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:445) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:599) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:92) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ObjectWriter._configAndWriteValue(ObjectWriter.java:800) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ObjectWriter.writeValueAsString(ObjectWriter.java:676) ~[jackson-databind-2.4.3.jar:2.4.3]
    at org.soluvas.json.JsonUtils.asJson(JsonUtils.java:54) ~[classes/:na]
    at id.co.bippo.product.rs.commerceplug.ProductOrServiceImplTest.productOrService(ProductOrServiceImplTest.java:41) [test-classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_20]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_20]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_20]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_20]
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) [junit-4.11.jar:na]
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) [junit-4.11.jar:na]
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) [junit-4.11.jar:na]
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) [junit-4.11.jar:na]
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70) [junit-4.11.jar:na]
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) [junit-4.11.jar:na]
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) [junit-4.11.jar:na]
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309) [junit-4.11.jar:na]
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) [.cp/:na]
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) [.cp/:na]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) [.cp/:na]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) [.cp/:na]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) [.cp/:na]
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) [.cp/:na]
Caused by: java.lang.IllegalArgumentException: Class org.springframework.hateoas.hal.Jackson2HalModule$HalLinkListSerializer has no default (no arg) constructor
    at com.fasterxml.jackson.databind.util.ClassUtil.createInstance(ClassUtil.java:370) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializerInstance(DefaultSerializerProvider.java:474) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BasicSerializerFactory.findSerializerFromAnnotation(BasicSerializerFactory.java:461) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._constructWriter(BeanSerializerFactory.java:708) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanProperties(BeanSerializerFactory.java:557) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.constructBeanSerializer(BeanSerializerFactory.java:344) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.findBeanSerializer(BeanSerializerFactory.java:263) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._createSerializer2(BeanSerializerFactory.java:222) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:152) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:1077) ~[jackson-databind-2.4.3.jar:2.4.3]
    at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1037) ~[jackson-databind-2.4.3.jar:2.4.3]
    ... 31 common frames omitted

Answer 1

I'm guessing you're doing more "integration" testing than unit testing if you need the converters setup as controllers don't return converted responses. I may suggest adding annotations like this to your test class

@RunWith(SpringJUnit4ClassRunner.class)
@WebAppConfiguration
@SpringApplicationConfiguration(classes = Application.class)

which will allow you to have this injection:

@Autowired
protected WebApplicationContext wac;

Which you can then pass to the MockMVC builder in your setup:

MockMvcBuilders.webAppContextSetup(wac).build()

Application.class would be something annotated with @ComponentScan that in turn gets all your configurations. You can pass them in explicitly too.

If you really want to generate the converter explicitly here's what we have:

public static HttpMessageConverter<Object> HALMessageConverter(){
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(new Jackson2HalModule());

    //TODO: need to figure out this curie provider stuff...more in production mode
    DefaultCurieProvider curieProvider = new DefaultCurieProvider("a", new UriTemplate("http://localhost:8080/myapp/rels/{rel}"));
    DefaultRelProvider relProvider = new DefaultRelProvider();

    objectMapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider));

    MappingJackson2HttpMessageConverter halConverter = new MappingJackson2HttpMessageConverter();
    halConverter.setObjectMapper(objectMapper);
    halConverter.setSupportedMediaTypes(Arrays.asList(MediaTypes.HAL_JSON));

    return halConverter;
}

and then you must register this converter with an MVC instance:

var mockMVC = MockMvcBuilders.standaloneSetup(controller)
            .setMessageConverters(HALMessageConverter())
            .build();

Looks like the media type and registering are what you may be missing.

Final note, that exception is something very different altogether. I've seen that when you instantiate an ObjectMapper that uses the existing mixin's but a different list serializer. This is because the resource mixin defines the HalListLinkSerializer as a serializer, but relies on proper instantiation. Not sure why you're getting that...guessing you have some annotation config going on somewhere...