Using Jackson, how can a list of known JSON properties be obtained for any arbitrary pojo class?

Question

Ideally, it would look much like this:

List props = objectMapper.getKnownProperties(MyPojo.class);

Alas, there is no such met

Answer 1

It's possible to ignore all annotations by using a dummy AnnotationIntrospector:

objectMapper.setAnnotationIntrospector(new AnnotationIntrospector(){
    @Override public Version version() {
        return Version.unknownVersion();
    }
});

Answer 2

With Jackson, you can introspect a class and get the available JSON properties using:

// Construct a Jackson JavaType for your class
JavaType javaType = mapper.getTypeFactory().constructType(MyDto.class);

// Introspect the given type
BeanDescription beanDescription = mapper.getSerializationConfig().introspect(javaType);

// Find properties
List<BeanPropertyDefinition> properties = beanDescription.findProperties();

If you have @JsonIgnoreProperties class level annotations, check this answer.

Answer 3

Depending on your exact needs, JsonFilter could also work (f.ex see http://www.cowtowncoder.com/blog/archives/2011/09/entry_461.html).

And for more advanced cases, BeanSerializerModifier does give you access to actual list of BeanPropertyWriters, which represent individual properties POJO has. From that, you could write a wrapper that enables/disables output dynamically. Or perhaps you can even combine approaches: modifier to get list of possible property names; then FilterProvider to dynamically add filter. Benefit of this would be that it is a very efficient way of implementing filtering.

Answer 4

Perhaps you could use Jackson's JSON Schema module to generate a schema for a class, then inspect the schema.