Serializing with Jackson (JSON) - getting “No serializer found”?

Question

I get the an exception when trying to serialize a very simple object using Jackson. The error:

org.codehaus.jackson.map.JsonMappingException: No serializer found for class MyPackage.TestA and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )

Below is the simple class and code to serialize.

Can anyone tell my why I get this error?

public class TestA {
    String SomeString = "asd";
}

TestA testA = new TestA();
ObjectMapper om = new ObjectMapper();
try {
    String testAString = om.writeValueAsString(testA); // error here!

    TestA newTestA = om.readValue(testAString, TestA.class);
} catch (JsonGenerationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (JsonMappingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

Answer 1

As already described, the default configuration of an ObjectMapper instance is to only access properties that are public fields or have public getters/setters. An alternative to changing the class definition to make a field public or to provide a public getter/setter is to specify (to the underlying VisibilityChecker) a different property visibility rule. Jackson 1.9 provides the ObjectMapper.setVisibility() convenience method for doing so. For the example in the original question, I'd likely configure this as

myObjectMapper.setVisibility(JsonMethod.FIELD, Visibility.ANY);

For Jackson >2.0:

myObjectMapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);

For more information and details on related configuration options, I recommend reviewing the JavaDocs on ObjectMapper.setVisibility().

Answer 2

For Jackson to serialize that class, the SomeString field needs to either be public (right now it's package level isolation) or you need to define getter and setter methods for it.

Answer 3

Add a

getter

and a

setter

and the problem is solved.

Answer 4

The problem in my case was Jackson was trying to serialize an empty object with no attributes nor methods.

As suggested in the exception I added the following line to avoid failure on empty beans:

For Jackson 1.9

myObjectMapper.configure(SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS, false);

For Jackson 2.X

myObjectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

You can find a simple example on jackson disable fail_on_empty_beans

Answer 5

If you can edit the class containing that object, I usually just add the annotation

import com.fasterxml.jackson.annotation.JsonIgnore;

@JsonIgnore 
NonSerializeableClass obj;

Answer 6

I had the same problem for a child class where I had control, object mapper was in a common module and was inaccessible. I solved it by adding this annotation for my child class whose object was to be serialized.

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)

Answer 7

This error is also thrown if you forget to add the .build() method onto your return status.

return Response.status(Status.OK);         // fails
return Response.status(Status.OK).build(); // works

I got the following error without build() method:

org.codehaus.jackson.map.JsonMappingException: No serializer found for class com.sun.jersey.core.spi.factory.ResponseBuilderImpl

Answer 8

SpringBoot2.0 ，I resolve it by follow code:

@Bean public ObjectMapper objectMapper() {
 return new ObjectMapper().disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);}

Answer 9

I had a similar problem with lazy loading via the hibernate proxy object. Got around it by annotating the class having lazy loaded private properties with:

@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})

Answer 10

For Oracle Java applications, add this after the ObjectMapper instantiation:

mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);

Answer 11

The problem may be because you have declared variable as private. If you change it to public, it works.

Better option is to use getter and setter methods for it.

This will solve the issue!

Answer 12

I found at least three ways of doing this:

1. Add public getters on your entity that you try to serialize;
2. Add an annotation at the top of the entity, if you don't want public getters. This will change the default for Jackson from Visbility=DEFAULT to @JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY) where any access modifiers are accepted;
3. Change your ObjectMapper globally by setting objectMapperInstance.setVisibility(JsonMethod.FIELD, Visibility.ANY);. This should be avoided if you don't need this functionality globally.

Choose based on your needs.

Answer 13

Here are the three options:

1. Data/class that's been accessed needs to be public
2. If not public, add getters & setters
3. Or add @JsonIgnore("context")

Answer 14

Please use this at class level for the bean:

@JsonIgnoreProperties(value={"hibernateLazyInitializer","handler","fieldHandler"})

Answer 15

adding setter and getter will also solve the issue as it fixed for me. For Ex:

public class TestA {
    String SomeString = "asd";

    public String getSomeString () {        return SomeString ;     }

    public void setSomeString (String SS ) {        SomeString = SS ;   } 
}

Answer 16

I just had only getters , after adding setters too , problems resolved.

Answer 17

in spring boot 2.2.5

after adding getter and setter

i added @JsonIgnore on top of the field.

Answer 18

Though I added getters and setters I was getting the same error. Later I found a bug, that is by Sonar's advice I cgahnged the getters and setters as protected which was causing the issue. Once I fixed that it worked as exppected.

Answer 19

If you use Lomdok libraray (https://projectlombok.org/) then add @Data (https://projectlombok.org/features/Data) annotation to your data object class.