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': 'ComputingandInformationsystems', 'id': 1, 'children': 'true', 'groups': [{ 'title': 'LeveloneCIS', 'id': 2, 'children': 'true', 'groups': [{ 'title': 'IntroToComputingandInternet', '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 IDs 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?
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Answer
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