Home » Java » Ignoring new fields on JSON objects using Jackson

Ignoring new fields on JSON objects using Jackson

Posted by: admin November 2, 2017 Leave a comment

Questions:

I’m using Jackson JSON library to convert some JSON objects to POJO classes on an android application. The problem is, the JSON objects might change and have new fields added while the application is published, but currently it will break even when a simple String field is added, which can safely be ignored.

Is there any way to tell Jackson to ignore newly added fields? (e.g. non-existing on the POJO objects)? A global ignore would be great.

Answers:

Jackson provides an annotation that can be used on class level (JsonIgnoreProperties).

Add the following to the top of your class (not to individual methods):

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

Depending on the jackson version you are using you would have to use a different import in the current version it is:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

in older versions it has been:

import org.codehaus.jackson.annotate.JsonIgnoreProperties;

Questions:
Answers:

In addition two 2 mechanisms already mentioned, there is also global feature that can be used to suppress all failures caused by unknown (unmapped) properties:

// jackson 1.9 and before
objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
// or jackson 2.0
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

This is the default used in absence of annotations, and can be convenient fallback.

Questions:
Answers:

Up to date and complete answer with Jackson 2


Using Annotation

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class MyMappingClass {

}

See JsonIgnoreProperties on Jackson online documentation.

Using Configuration

Less intrusive than annotation.

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

ObjectReader objectReader = objectMapper.reader(MyMappingClass.class);
MyMappingClass myMappingClass = objectReader.readValue(json);

See FAIL_ON_UNKNOWN_PROPERTIES on Jackson online documentation.

Questions:
Answers:

If using a pojo class based on JSON response. If chances are there that json changes frequently declare at pojo class level:

@JsonIgnoreProperties(ignoreUnknown = true)

and at the objectMapper add this if you are converting:

objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

So that code will not break.

Questions:
Answers:

Make sure that you place the @JsonIgnoreProperties(ignoreUnknown = true) annotation to the parent POJO class which you want to populate as a result of parsing the JSON response and not the class where the conversion from JSON to Java Object is taking place.

Questions:
Answers:

As stated above the annotations only works if this is specified in the parent POJO class and not the class where the conversion from JSON to Java Object is taking place.

The other alternative without touching the parent class and causing disruptions is to implement your own mapper config only for the mapper methods you need for this.

Also the package of the Deserialization feature has been moved.
DeserializationConfig.FAIL_ON_UNKNOWN_PROPERTIES to
DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES

import org.codehaus.jackson.map.DeserializationConfig;
...
objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

Questions:
Answers:

Starting with Jackson version 2.4 and above there have been some changes.
Here is how you do it now:

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

………………………………………………………………..

 ObjectMapper mapper = new ObjectMapper();
    // to prevent exception when encountering unknown property:
 mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

Note: The @annotation based solution remains the same so if you like to use that see the other answers.

For more information see the 10 minutes Configuration tutorial at: https://github.com/FasterXML/jackson-databind

Questions:
Answers:

I’m using jackson-xxx 2.8.5.Maven Dependency like:

<dependencies>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.8.5</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.8.5</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.8.5</version>
    </dependency>

</dependencies>

First,If you want ignore unknown properties globally.you can config ObjectMapper.
Like below:

ObjectMapper objectMapper = new ObjectMapper();

objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

If you want ignore some class,you can add annotation @JsonIgnoreProperties(ignoreUnknown = true) on your class like:

@JsonIgnoreProperties(ignoreUnknown = true)
public class E1 {

    private String t1;

    public String getT1() {
        return t1;
    }

    public void setT1(String t1) {
        this.t1 = t1;
    }
}

Questions:
Answers:

it can be achieved 2 ways:

  1. Mark the POJO to ignore unknown properties

    @JsonIgnoreProperties(ignoreUnknown = true)
    
  2. Configure ObjectMapper that serializes/De-serializes the POJO/json as below:

    ObjectMapper mapper =new ObjectMapper();            
    // for Jackson version 1.X        
    mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    // for Jackson version 2.X
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false) 
    
Questions:
Answers:

You can annotate the specific property in your POJO with @JsonIgnore.