Jackson Unmarshalling JSON with Unknown Properties

Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.

End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

>> Automated End-to-End Testing With Playwright

1. Overview

In this tutorial, we’re going to take a look at the unmarshalling process with Jackson 2.x, specifically how to deal with JSON content with unknown properties.

To dig deeper and learn other cool things we can do with Jackson, we can check out the main Jackson tutorial.

Jackson Ignore Properties on Marshalling

Control your JSON Output - Ignore certain fields directly, by name or by type (with mixins) for Jackson bliss.

Jackson - Change Name of Field

Jackson - Change the name of a field to adhere to a specific JSON format.

2. Unmarshall a JSON With Additional/Unknown Fields

JSON input comes in all shapes and sizes, and most of the time, we need to map it to predefined Java objects with a set number of fields. The goal is to simply ignore any JSON properties that cannot be mapped to an existing Java field.

For example, say we need to unmarshal JSON to the following Java entity:

public class MyDto {

    private String stringValue;
    private int intValue;
    private boolean booleanValue;

    // standard constructor, getters and setters 
}

**2.1. UnrecognizedPropertyException on Unknown Fields**

Trying to unmarshal a JSON with unknown properties to this simple Java Entity will lead to a com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException:

@Test(expected = UnrecognizedPropertyException.class)
public void givenJsonHasUnknownValues_whenDeserializingAJsonToAClass_thenExceptionIsThrown()
  throws JsonParseException, JsonMappingException, IOException {
    String jsonAsString =
        "{\"stringValue\":\"a\"," +
        "\"intValue\":1," +
        "\"booleanValue\":true," +
        "\"stringValue2\":\"something\"}";
    ObjectMapper mapper = new ObjectMapper();

    MyDto readValue = mapper.readValue(jsonAsString, MyDto.class);

    assertNotNull(readValue);
}

This will fail with the following exception:

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: 
Unrecognized field "stringValue2" (class org.baeldung.jackson.ignore.MyDto), 
not marked as ignorable (3 known properties: "stringValue", "booleanValue", "intValue"])

2.2. Dealing With Unknown Fields Using the ObjectMapper

We can now configure the full ObjectMapper to ignore unknown properties in the JSON:

new ObjectMapper()
  .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)

We should then be able to read this kind of JSON into a predefined Java entity:

@Test
public void givenJsonHasUnknownValuesButJacksonIsIgnoringUnknownFields_whenDeserializing_thenCorrect()
  throws JsonParseException, JsonMappingException, IOException {
 
    String jsonAsString =
        "{\"stringValue\":\"a\"," +
        "\"intValue\":1," +
        "\"booleanValue\":true," +
        "\"stringValue2\":\"something\"}";
    ObjectMapper mapper = new ObjectMapper()
      .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    MyDto readValue = mapper.readValue(jsonAsString, MyDto.class);

    assertNotNull(readValue);
    assertThat(readValue.getStringValue(), equalTo("a"));
    assertThat(readValue.isBooleanValue(), equalTo(true));
    assertThat(readValue.getIntValue(), equalTo(1));
}

2.3. Dealing With Unknown Fields at the Class Level

We can also mark a single class as accepting unknown fields, instead of the entire Jackson ObjectMapper:

@JsonIgnoreProperties(ignoreUnknown = true)
public class MyDtoIgnoreUnknown { ... }

Now we should be able to test the same behavior as before. The unknown fields are simply ignored, and only known fields are mapped:

@Test
public void givenJsonHasUnknownValuesButUnknownFieldsAreIgnoredOnClass_whenDeserializing_thenCorrect() 
  throws JsonParseException, JsonMappingException, IOException {
 
    String jsonAsString =
        "{\"stringValue\":\"a\"," +
        "\"intValue\":1," +
        "\"booleanValue\":true," +
        "\"stringValue2\":\"something\"}";
    ObjectMapper mapper = new ObjectMapper();

    MyDtoIgnoreUnknown readValue = mapper
      .readValue(jsonAsString, MyDtoIgnoreUnknown.class);

    assertNotNull(readValue);
    assertThat(readValue.getStringValue(), equalTo("a"));
    assertThat(readValue.isBooleanValue(), equalTo(true));
    assertThat(readValue.getIntValue(), equalTo(1));
}

3. Unmarshall an Incomplete JSON

Similar to additional unknown fields, unmarshalling an incomplete JSON, a JSON that doesn’t contain all the fields in the Java class, isn’t a problem with Jackson:

@Test
public void givenNotAllFieldsHaveValuesInJson_whenDeserializingAJsonToAClass_thenCorrect() 
  throws JsonParseException, JsonMappingException, IOException {
    String jsonAsString = "{"stringValue":"a","booleanValue":true}";
    ObjectMapper mapper = new ObjectMapper();

    MyDto readValue = mapper.readValue(jsonAsString, MyDto.class);

    assertNotNull(readValue);
    assertThat(readValue.getStringValue(), equalTo("a"));
    assertThat(readValue.isBooleanValue(), equalTo(true));
}

4. Conclusion

In this article, we discussed deserializing a JSON with additional, unknown properties using Jackson.

This is one of the most common things to configure when working with Jackson, since we often need to map JSON results of external REST APIs to an internal Java representation of the entities of the API.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.