Converting Json to Java

Question

Hi all, I want to be able to access properties from a json string within my java action method. The string is available by simply saying myJsonString = object.getJson(); Below is an example of what the string can look like:

{'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':[]}]}]}

In this string every json object contains an array of other json objects. The intention is to extract a list of id's where any given object possessing a group property that contains other json objects. 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?

Thank you, Kind regards.

Answer 1

If you visit this page you will find several Java classes that can help with this. For example, the JSONObject and the JSONArray classes. They are designed to read in a JSON String and provide access to their properties via a get() method.

Answer 2

The XStream library also supports JSON: http://xstream.codehaus.org/json-tutorial.html.

Answer 3

We have chosen Google Gson because it has the best support for Generics and nested beans.

Your example can be solved 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().

Answer 4

If you use any kind of special maps with keys or values also of special maps, you will find it's not contemplated by the implementation of google.

Answer 5

Bewaaaaare of Gson! It's very cool, very great, but the second you want to do anything other than simple objects, you could easily need to start building your own serializers (which isn't that hard). Also, if you have an array of Objects, and you deserialize some json into that array of Objects, the true types are LOST! The full objects won't even be copied! Use XStream.. Which, if using the jsondriver and setting the proper settings, will encode ugly types into the actual json, so that you don't loose anything. A small price to pay (ugly json) for true serialization.