Jackson JSON Views

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1. Overview

In this tutorial, we’ll go over how to use Jackson JSON Views to serialize/deserialize objects, customize the views and finally – how to start integrating with Spring.

2. Serialize using JSON Views

First – let’s go through a simple example – serialize an object with @JsonView.

Here is our view:

public class Views {
    public static class Public {
    }
}

And the “User” entity:

public class User {
    public int id;

    @JsonView(Views.Public.class)
    public String name;
}

Now let’s serialize a “User” instance using our view:

@Test
public void whenUseJsonViewToSerialize_thenCorrect() 
  throws JsonProcessingException {
    User user = new User(1, "John");

    ObjectMapper mapper = new ObjectMapper();
    mapper.disable(MapperFeature.DEFAULT_VIEW_INCLUSION);

    String result = mapper.writerWithView(Views.Public.class)
                          .writeValueAsString(user);

    assertThat(result, containsString("John"));
    assertThat(result, not(containsString("1")));
}

Note how, because we’re serializing with a specific view active, we’re seeing only the right fields being serialized.

It’s also important to understand, that – by default – all properties not explicitly marked as being part of a view, are serialized. We are disabling that behavior with the handy DEFAULT_VIEW_INCLUSION feature.

3. Use Multiple JSON Views

Next – let’s see how to use multiple JSON Views – each has different fields as in the following example:

Here we have to views where Internal extends Public, with the internal view extending the public one:

public class Views {
    public static class Public {
    }

    public static class Internal extends Public {
    }
}

And here is our entity “Item” where only the fields id and name are included in the Public view:

public class Item {
    @JsonView(Views.Public.class)
    public int id;

    @JsonView(Views.Public.class)
    public String itemName;

    @JsonView(Views.Internal.class)
    public String ownerName;
}

If we use the Public view to serialize – only id and name will be serialized to JSON:

@Test
public void whenUsePublicView_thenOnlyPublicSerialized() 
  throws JsonProcessingException {
    Item item = new Item(2, "book", "John");

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writerWithView(Views.Public.class)
                          .writeValueAsString(item);

    assertThat(result, containsString("book"));
    assertThat(result, containsString("2"));

    assertThat(result, not(containsString("John")));
}

But if we use the Internal view to perform the serialization, all fields will be part of the JSON output:

@Test
public void whenUseInternalView_thenAllSerialized() 
  throws JsonProcessingException {
    Item item = new Item(2, "book", "John");

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writerWithView(Views.Internal.class)
                          .writeValueAsString(item);

    assertThat(result, containsString("book"));
    assertThat(result, containsString("2"));

    assertThat(result, containsString("John"));
}

4. Deserialize using JSON Views

Now – let’s see how to use JSON Views to deserialize objects – specifically, a User instance:

@Test
public void whenUseJsonViewToDeserialize_thenCorrect() 
  throws IOException {
    String json = "{\"id\":1,\"name\":\"John\"}";

    ObjectMapper mapper = new ObjectMapper();
    User user = mapper.readerWithView(Views.Public.class)
                      .withType(User.class)
                      .readValue(json);

    assertEquals(1, user.getId());
    assertEquals("John", user.getName());
}

Note how we’re using the readerWithView() API to create an ObjectReader using the given view.

5. Customize JSON Views

Next – let’s see how to customize JSON Views. In the next example – we want to make the User “name” UpperCase in the serialization result.

We will use BeanPropertyWriter and BeanSerializerModifier to customize our JSON view. First – here is the BeanPropertyWriter UpperCasingWriter to transform the User name to upper case:

public class UpperCasingWriter extends BeanPropertyWriter {
    BeanPropertyWriter _writer;

    public UpperCasingWriter(BeanPropertyWriter w) {
        super(w);
        _writer = w;
    }

    @Override
    public void serializeAsField(Object bean, JsonGenerator gen, 
      SerializerProvider prov) throws Exception {
        String value = ((User) bean).name;
        value = (value == null) ? "" : value.toUpperCase();
        gen.writeStringField("name", value);
    }
}

And here is the BeanSerializerModifier to set the User name BeanPropertyWriter with our custom UpperCasingWriter:

public class MyBeanSerializerModifier extends BeanSerializerModifier{

    @Override
    public List<BeanPropertyWriter> changeProperties(
      SerializationConfig config, BeanDescription beanDesc, 
      List<BeanPropertyWriter> beanProperties) {
        for (int i = 0; i < beanProperties.size(); i++) {
            BeanPropertyWriter writer = beanProperties.get(i);
            if (writer.getName() == "name") {
                beanProperties.set(i, new UpperCasingWriter(writer));
            }
        }
        return beanProperties;
    }
}

Now – let’s serialize a User instance using the modified Serializer:

@Test
public void whenUseCustomJsonViewToSerialize_thenCorrect() 
  throws JsonProcessingException {
    User user = new User(1, "John");
    SerializerFactory serializerFactory = BeanSerializerFactory.instance
      .withSerializerModifier(new MyBeanSerializerModifier());

    ObjectMapper mapper = new ObjectMapper();
    mapper.setSerializerFactory(serializerFactory);

    String result = mapper.writerWithView(Views.Public.class)
                          .writeValueAsString(user);

    assertThat(result, containsString("JOHN"));
    assertThat(result, containsString("1"));
}

6. Using JSON Views with Spring

Finally – let’s take a quick look at using JSON views with the Spring Framework. We can leverage the @JsonView annotation to customize our JSON response at the API level.

In the following example – we used the Public view to respond:

@JsonView(Views.Public.class)
@RequestMapping("/items/{id}")
public Item getItemPublic(@PathVariable int id) {
    return ItemManager.getById(id);
}

The response is:

{"id":2,"itemName":"book"}

And when we used the Internal view as follows:

@JsonView(Views.Internal.class)
@RequestMapping("/items/internal/{id}")
public Item getItemInternal(@PathVariable int id) {
    return ItemManager.getById(id);
}

That was the response:

{"id":2,"itemName":"book","ownerName":"John"}

If you want to dive deeper into using the views with Spring 4.1, you should check out the Jackson improvements in Spring 4.1.

7. Conclusion

In this quick tutorial, we had a look at the Jackson JSON views and the @JsonView annotation. We learned how to use JSON Views to have fine-grained control over our serialize/deserialize process – using a single or multiple views.

I usually post about Jackson and JSON stuff on Google+ - you can follow me there: