feat: allow json-jackson to auto-discover modules

[tirz]

Currently, we cannot register module to jersey-media-json-jackson.
This MR will allow json-jackson to auto-discover the modules in use.

We may for example add to pom.xml:

<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-datatype-jdk8</artifactId>
    <version>2.8.4</version>
</dependency>

Will fix: #4311

[jansupol]

I am not sure about this. The thing is that the JsonMapperConfigurator code is repackaged from Jackson 2.10.1. As long as a new version of Jackson is repackaged, the contributed code of this PR could be replaced again (and hence lost).

Ideally, the change would be made to Jackson itself.

On the other hand, this is not the first PR we register that asks for changing the Jackson classes (Note that for any change like this in the 3rd party content we probably need to ask Eclipse Legal to approve). We ought to think about some kind of wrapper, if possible.

[jansupol]

It looks like it is possible to pass the ObjectMapper to JacksonJsonProvider. We use it directly in JacksonFeature as well as in Jersey FilteringJacksonJaxbJsonProvider.
Assumingly the solution is to

• Create a DirectJacksonJsonProvider class that has a constructor that passes the ObjectMapper to Jackson's JacksonJsonProvider. Use the DirectJacksonJsonProvider in JacksonFeature.
• Create a constructor in Jersey FilteringJacksonJaxbJsonProvider that passes the ObjectMapper to Jackson's JacksonJsonProvider.

Create

package org.glassfish.jersey.jackson.internal;

import com.fasterxml.jackson.databind.ObjectMapper;

public class DefaultJacksonObjectMapper extends ObjectMapper {
    public DefaultJacksonObjectMapper() {
       findAndRegisterModules();
    }
}

And create the constructor, such as (also in DirectJacksonJsonProvider):

public final class FilteringJacksonJaxbJsonProvider extends JacksonJaxbJsonProvider {

    public FilteringJacksonJaxbJsonProvider() {
        super(new DefaultJacksonObjectMapper(), DEFAULT_ANNOTATIONS);
    }

Would that work?

[tirz]

Unfortunately, with:

@Singleton
public final class DirectJacksonJaxbJsonProvider extends JacksonJsonProvider {

    public DirectJacksonJaxbJsonProvider() {
        super(new DefaultJacksonObjectMapper(), BASIC_ANNOTATIONS);
    }

    public DirectJacksonJaxbJsonProvider(final Annotations... annotationsToUse) {
        super(new DefaultJacksonObjectMapper(), annotationsToUse);
    }
}

final class DefaultJacksonObjectMapper extends ObjectMapper {

    DefaultJacksonObjectMapper() {
        findAndRegisterModules();
    }
}

We are setting ObjectMapper by an instance of DefaultJacksonObjectMapper at each time, which mean we cannot customize the injection like on this example:

public class ObjectMapperContextResolver implements ContextResolver<ObjectMapper> {

    @Context
    private HttpHeaders headers;

    private final ObjectMapper mapper;

    public ObjectMapperContextResolver() {
        mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
        return mapper;
    }
}

I tried a simple:

@Singleton
public class DefaultJacksonJaxbJsonProvider extends JacksonJaxbJsonProvider {

    public DefaultJacksonJaxbJsonProvider() {
        findAndRegisterModules();
    }

    public DefaultJacksonJaxbJsonProvider(final Annotations... annotationsToUse) {
        super(annotationsToUse);
        findAndRegisterModules();
    }

    private void findAndRegisterModules() {
        final ObjectMapper defaultMapper = _mapperConfig.getDefaultMapper();
        if (Objects.nonNull(defaultMapper)) {
            defaultMapper.findAndRegisterModules();
        }

        final ObjectMapper mapper = _mapperConfig.getConfiguredMapper();
        if (Objects.nonNull(mapper)) {
            mapper.findAndRegisterModules();
        }
    }
}

But it seams to break the JDK8 (-Ptravis_e2e_skip) and JDK15 (-Ptravis_e2e) tests :/

I will investigate it.

[jansupol]

The Travis is good at exposing imperfections in tests, so the tests fail intermittently. I can see all the tests passed now with this PR.

[jansupol]

It looks good. Please update the copyright years to 2020 and add a copyright header to the new file.

I would not mind a test for the provided functionality, too.

[jansupol]

Filed CQ 22138 for jackson-modules-java8.

[jansupol]

The CQ has been approved