Using customized ObjectWriter with Jersey

Question

I am developing a REST webservice. Jersey as jax-rs provider and Jackson for serialization/deserialization. I also develop the client based on Retrofit2.

My class hierarchy is provided by a third-party library and all classes descend from a root base class BaseObject. Some of those classes have undesirable getters, e.g. isEmpty, that I want to ignore on serialization (Note that it is important that they do not get serialized at all and using FAIL_ON_UNKNOWN_PROPERTIES on deserialization is not enough in my case).

I have used Jackson @JsonFilter on BaseClass using Mixins. To apply a filter, as far as I know, one has to use the following:

new ObjectMapper().writer(filterProvider).writeValueAsString...

Everything is ok up to here: the undesired property is successfully filtered from the produced json.

Now I have to configure Jersey and Retrofit2 to use my customized json serializer/deserializer.

For Jersey, serialization/deserialization can be configured using a Provider class that implements ContextResolver<ObjectMapper> and returning customized ObjectMapper in getContext(Class<?> type) method.

Similarly in Retrofit2, by using Retrofit.Builder().addConverterFactory(JacksonConverterFactory.create(objectMapper)), one can customize serialization/deserialization.

THE PROBLEM IS THAT new ObjectMapper().writer(filterProvider) is of type ObjectWriter and not of type ObjectMapper. How can I tell Jersey and Retrofit2 to use my customized ObjectWriter which uses my filters?

Answer 1

Since version 2.6 of Jackson it has the 'setFilterProvider' method for an ObjectMapper. I didn't try it but the documentation has the description for this: https://fasterxml.github.io/jackson-databind/javadoc/2.6/com/fasterxml/jackson/databind/ObjectMapper.html#setFilterProvider-com.fasterxml.jackson.databind.ser.FilterProvider-. You can try i think because the description fits for your case.

I built a test service with Jersey 2.7 and Jackson 2.9.5. it works fine but you have to know some tricks to run it.

In pom.xml add Jersey and Jackson:

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.glassfish.jersey</groupId>
            <artifactId>jersey-bom</artifactId>
            <version>${jersey.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
<dependencies>
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet-core</artifactId>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-jackson</artifactId>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>${jackson.version}</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>${jackson.version}</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>${jackson.version}</version>
    </dependency>
</dependencies>
<properties>
    <jersey.version>2.7</jersey.version>
    <jackson.version>2.9.5</jackson.version>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

You have to define this dependence:

    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-jackson</artifactId>
    </dependency>

it's mandatory.

In web.xml you have to make the ref to configuration of your service:

<web-app version="2.5"
     xmlns="http://java.sun.com/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
    <servlet-name>Jersey Web Application</servlet-name>
    <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
    <init-param>
        <param-name>org.glassfish.jersey.server.ResourceConfig</param-name>
        <param-value>com.home.MyApplication</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

MyApplication.java:

package com.home;

import org.glassfish.jersey.jackson.JacksonFeature;
import org.glassfish.jersey.server.ResourceConfig;

import javax.ws.rs.ApplicationPath;

@ApplicationPath("/webapi")
public class MyApplication extends ResourceConfig {

    public MyApplication() {

        register(ObjectMapperProvider.class);
        register(JacksonFeature.class);
        register(MyResource.class);

    }
}

With a custom ObjectMapperProvider you have to register a JacksonFeature.class because without it Jersey doesn't use the custom ObjectMapperProvider.

ObjectMapperProvider.java:

package com.home;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;
import javax.ws.rs.ext.ContextResolver;
import javax.ws.rs.ext.Provider;

@Provider
public class ObjectMapperProvider implements ContextResolver<ObjectMapper>{

    final ObjectMapper defaultObjectMapper;

    public ObjectMapperProvider() {
        defaultObjectMapper = createDefaultMapper();
    }

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

    public static ObjectMapper createDefaultMapper() {

        final ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
        mapper.setFilters(new SimpleFilterProvider().addFilter("dataFilter", SimpleBeanPropertyFilter.serializeAllExcept("region", "city")));
        return mapper;

    }
}

To define a filter use the 'setFilters' methods. This method is deprecated but the Jersey's library which called 'jersey-hk2' doesn't know the new method 'setFilterProvider' and throws an exception. With the old method everything works fine.

A business object with @JsonFilter:

@JsonFilter("dataFilter")
public class SimpleData {

    @JsonProperty("name")
    String firstName;

    @JsonProperty("secondName")
    String lastName;

    @JsonProperty("country")
    String country;

    @JsonProperty("region")
    String region;

    @JsonProperty("city")
    String city;

    @JsonProperty("genre")
    String genre;

    public SimpleData() {

        this.firstName = "Bryan";
        this.lastName = "Adams";

        this.country = "Canada";
        this.region = "Ontario";
        this.city = "Kingston";
        this.genre = "Rock";

    }

    public String getFirstName() {    return firstName;       }
    public void setFirstName(String firstName) {  this.firstName = firstName;  }
    public String getLastName() {   return lastName;    }
    public void setLastName(String lastName) {  this.lastName = lastName;       }
    public String getCountry() {    return country;    }
    public void setCountry(String country) {  this.country = country;      }
    public String getRegion() {   return region;     }
    public void setRegion(String region) {   this.region = region;       }
    public String getCity() {  return city;     }
    public void setCity(String city) {   this.city = city;     }
    public String getGenre() {   return genre;      }
    public void setGenre(String genre) {    this.genre = genre;     }
}

MyResource.java:

@Path("myresource")
public class MyResource {


    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public SimpleData getIt() {

        return new SimpleData();

    }
}

A filtered result: