Using conditions to dynamically exclude POJO property in Jackson json serialization

Question

I have a requirement to dynamically exclude certain property within a List of a defined POJO. The main POJO to be serialized is:

public class Foo
{
    List<Bar> bar;

    public void setBar(List<Bar> bar)
    {
        this.bar = bar;
    }

    public List<Bar> getBar()
    {
        return this.bar;
    }

    public static class Bar
    {
        private int id;
        private boolean ignoreId;
        private String name;

        public void setId(int id)
        {
            this.id = id;
        }

        public int getId()
        {
            return this.id;
        }

        public void setIgnoreId(boolean ignoreId)
        {
            this.ignoreId = ignoreId;
        }

        public boolean isIgnoreId()
        {
            return this.ignoreId;
        }

        public void setName(String name)
        {
            this.name = name;
        }

        public String getName()
        {
            return this.name;
        }
    }
}

id is to be ignored if ignoreId = true, like so:

[
    { "id": "1", "name": "one" },
    { "name": "two" }
    { "name": "three" }
    { "id": "4", "name": "four" }
]

At the moment, I have tried using JsonFilter and JacksonJsonViews but couldn't get the required output. I would be glad if any pointer can be given towards achieving this.

Answer 1

You should write a custom Jackson filter which would filter out a POJO property depending on other property value. You should override the PropertyFilter.serializeAsField() method to get access to the instance of the serialized object. Here is an example:

public class JacksonFilter2 {
    @JsonFilter("filter")
    public static class Bar {
        public final int id;
        @JsonIgnore
        public final boolean ignoreId;
        public final String name;

        public Bar(int id, boolean ignoreId, String name) {
            this.id = id;
            this.ignoreId = ignoreId;
            this.name = name;
        }
    }

    public static class ExcludeIdFilter extends SimpleBeanPropertyFilter {

        @Override
        protected boolean include(BeanPropertyWriter writer) {
            return true;
        }

        @Override
        protected boolean include(PropertyWriter writer) {
            return true;
        }

        @Override
        public void serializeAsField(Object pojo,
                                     JsonGenerator jgen,
                                     SerializerProvider provider,
                                     PropertyWriter writer) throws Exception {
            if (pojo instanceof Bar
                    && "id".equals(writer.getName())
                    && ((Bar) pojo).ignoreId) {
               writer.serializeAsOmittedField(pojo, jgen, provider);
            } else {
                super.serializeAsField(pojo, jgen, provider, writer);
            }
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        List<Bar> bars = Arrays.asList(new Bar(1, false, "one"),  new Bar(2, true, "two"));
        ObjectMapper mapper = new ObjectMapper();
        mapper.setFilters(new SimpleFilterProvider().addFilter("filter", new ExcludeIdFilter()));
        System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(bars));
    }

}

Output:

[ {
  "id" : 1,
  "name" : "one"
}, {
  "name" : "two"
} ]