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().