Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

How should I structure my Java object?

Below is what your object model could look like. MOXy's JSON binding leverages JAXB annotations for mapping the domain model to JSON, so I have included those as well. JAXB implementations have default rules for mapping field/property names, but since your document differs from the default each field had to be annotated.

MyResult

package forum11001458;

import javax.xml.bind.annotation.*;

@XmlRootElement(name="MyResult")
public class MyResult {

    @XmlElement(name="AccountID")
    private String accountID;

    @XmlElement(name="User")
    private User user;

    @XmlElement(name="Result")
    private Result result;

}

User

package forum11001458;

import javax.xml.bind.annotation.XmlElement;

public class User {

    @XmlElement(name="Name")
    private String name;

    @XmlElement(name="Email")
    private String email;

}

Result

package forum11001458;

import javax.xml.bind.annotation.XmlElement;

public class Result {

    @XmlElement(name="Course")
    private String course;

    @XmlElement(name="Score")
    private String score;

}

What Json library can I use for this?

Below is how you can use MOXy to do the JSON binding:

jaxb.properties

To use MOXy as your JAXB provider you need to include a file called jaxb.properties with the following entry in the same package as your domain model:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

Demo

Note how MOXy's JSON binding does not require any compile time dependencies. All the necessary APIs are available in Java SE 6. You can add the necessary supporting APIs if you are using Java SE 5.

package forum11001458;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(MyResult.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setProperty("eclipselink.media-type", "application/json");
        File json = new File("src/forum11001458/input.json");
        Object myResult = unmarshaller.unmarshal(json);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty("eclipselink.media-type", "application/json");
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(myResult, System.out);
    }

}

input.json/Output

{
   "MyResult" : {
      "AccountID" : "12345",
      "User" : {
         "Name" : "blah blah",
         "Email" : "[email protected]"
      },
      "Result" : {
         "Course" : "blah",
         "Score" : "10.0"
      }
   }
}

To convert your object in JSON with Jackson:

import com.fasterxml.jackson.databind.ObjectMapper; 
import com.fasterxml.jackson.databind.ObjectWriter; 

ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
String json = ow.writeValueAsString(object);

Using org.json library:

try {
     JSONObject jsonObject = new JSONObject("{\"phonetype\":\"N95\",\"cat\":\"WP\"}");
}catch (JSONException err){
     Log.d("Error", err.toString());
}

I looked at Google's Gson as a potential JSON plugin. Can anyone offer some form of guidance as to how I can generate Java from this JSON string?

Google Gson supports generics and nested beans. The [] in JSON represents an array and should map to a Java collection such as List or just a plain Java array. The {} in JSON represents an object and should map to a Java Map or just some JavaBean class.

You have a JSON object with several properties of which the groups property represents an array of nested objects of the very same type. This can be parsed with Gson the following way:

package com.stackoverflow.q1688099;

import java.util.List;
import com.google.gson.Gson;

public class Test {

    public static void main(String... args) throws Exception {
        String json = 
            "{"
                + "'title': 'Computing and Information systems',"
                + "'id' : 1,"
                + "'children' : 'true',"
                + "'groups' : [{"
                    + "'title' : 'Level one CIS',"
                    + "'id' : 2,"
                    + "'children' : 'true',"
                    + "'groups' : [{"
                        + "'title' : 'Intro To Computing and Internet',"
                        + "'id' : 3,"
                        + "'children': 'false',"
                        + "'groups':[]"
                    + "}]" 
                + "}]"
            + "}";

        // Now do the magic.
        Data data = new Gson().fromJson(json, Data.class);

        // Show it.
        System.out.println(data);
    }

}

class Data {
    private String title;
    private Long id;
    private Boolean children;
    private List<Data> groups;

    public String getTitle() { return title; }
    public Long getId() { return id; }
    public Boolean getChildren() { return children; }
    public List<Data> getGroups() { return groups; }

    public void setTitle(String title) { this.title = title; }
    public void setId(Long id) { this.id = id; }
    public void setChildren(Boolean children) { this.children = children; }
    public void setGroups(List<Data> groups) { this.groups = groups; }
    
    public String toString() {
        return String.format("title:%s,id:%d,children:%s,groups:%s", title, id, children, groups);
    }
}

Fairly simple, isn't it? Just have a suitable JavaBean and call Gson#fromJson().

See also:

• Json.org - Introduction to JSON
• Gson User Guide - Introduction to Gson