Create simple JSON structure using jackson

Question

I'd just like to create the Jackson mapping equivalent of the below :

{\"isDone\": true}

I think I need to create a class like this :

public class Status {

    private boolean isDone;

    public boolean isDone{
        return this.isDone;
    }

    public void setDone(boolean isDone){
        this.isDone = isDone;
    }
}

But how do I instatiate it and then write the JSON to a string ?

Answer 1

A problem with your example and Jackson is the default choices of JSON property names: Jackson will see isDone and setDone and choose done as the JSON property name. You can override this default choice using the JsonProperty annotation:

public class Status
{
    private boolean isDone;

    @JsonProperty("isDone")
    public boolean isDone()
    {
        return this.isDone;
    }

    @JsonProperty("isDone")
    public void setDone(boolean isDone)
    {
        this.isDone = isDone;
    }
}

Then:

Status instance = new Status();
String jsonString = null;

instance.setDone(true);
ObjectMapper mapper = new ObjectMapper();

jsonString = mapper.writeValueAsString(instance);

Now jsonString contains { "isDone" : true }. Note that you can also write the string to an OutputStream using ObjectMapper.writeValue(OutputStream, Object), or to a Writer using ObjectMapper.writeValue(Writer, Object).

In this case you really only need the JsonProperty annotation on either of your accessors, but not both. Just annotating isDone will get you the JSON property name that you want.

An alternative to using the JsonProperty annotation is to rename your accessors setIsDone/getIsDone. Then the annotations are unnecessary.

See the quick and dirty Jackson tutorial: Jackson in 5 minutes. Understanding of the specific properties came from looking through the docs for Jackson annotations.

Answer 2

Right. The code needed:

ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(new Status()));