Convert a Json String to Object in Java Me

How to convert the following json string to java object?

No need to go with GSON for this; Jackson can do either plain Maps/Lists:

ObjectMapper mapper = new ObjectMapper();
Map<String,Object> map = mapper.readValue(json, Map.class);

or more convenient JSON Tree:

JsonNode rootNode = mapper.readTree(json);

By the way, there is no reason why you could not actually create Java classes and do it (IMO) more conveniently:

public class Library {
  @JsonProperty("libraryname")
  public String name;

  @JsonProperty("mymusic")
  public List<Song> songs;
}
public class Song {
  @JsonProperty("Artist Name") public String artistName;
  @JsonProperty("Song Name") public String songName;
}

Library lib = mapper.readValue(jsonString, Library.class);

Convert a JSON string to object in Java ME?

I used a few of them and my favorite is,

http://code.google.com/p/json-simple/

The library is very small so it's perfect for J2ME.

You can parse JSON into Java object in one line like this,

JSONObject json = (JSONObject)new JSONParser().parse("{\"name\":\"MyNode\", \"width\":200, \"height\":100}");
System.out.println("name=" + json.get("name"));
System.out.println("width=" + json.get("width"));

How to convert jsonString to JSONObject in Java

Using org.json library:

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

How to convert JSON string into List of Java object?

You are asking Jackson to parse a StudentList. Tell it to parse a List (of students) instead. Since List is generic you will typically use a TypeReference

List<Student> participantJsonList = mapper.readValue(jsonString, new TypeReference<List<Student>>(){});

Converting a JSON string into an object with a list of objects inside it - Java

You have to create another class say Output as

import java.util.List;

public class Output {
    public List<Token> getTokens() {
        return tokens;
    }

    public void setTokens(List<Token> tokens) {
        this.tokens = tokens;
    }

    private List<Token> tokens;
}

and then use

Output output = new Gson().fromJson(json, Output.class);

then you can use output to get list of tokens and go further for suggestion etc

Converting JSON data to Java object

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

How to convert the following JSON String to POJO

I think it should work. I've executed this code and it works fine. Here is my example.

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;

public class TestJackson {

public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        String testJson = "{\n" + "  \"user\": {\n" + "    \"0\": {\n" + "      \"firstName\": \"Monica\",\n" + "      \"lastName\": \"Belluci\"\n" + "    },\n" + "    \"1\": {\n" + "      \"firstName\": \"John\",\n" + "      \"lastName\": \"Smith\"\n" + "    },\n" + "    \"2\": {\n" + "      \"firstName\": \"Owen\",\n" + "      \"lastName\": \"Hargreaves\"\n" + "    }\n" + "  }\n" + "}";
        User readValue = mapper.readValue(testJson, User.class);
        System.out.println("readValue = " + readValue);
    }
}

and the User.class:

import java.util.HashMap;
import java.util.Map;

class User {
    private Map<String, MyObject> user = new HashMap<String, MyObject>();

    public Map<String, MyObject> getUser() {
        return user;
    }

    public void setUser(Map<String, MyObject> user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "User{" +
                "user=" + user +
                '}';
    }
}

class MyObject {
    private String firstName;
    private String lastName;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return "MyObject{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                '}';
    }
}

Convert a JSON string to object in J2ME?

The problem with such JSON libraries,
is that they generate JSONObjects from
strings, not plain Objects. My
function requires an Object, so can I
stuff down a JSONObject into it??

A "plain Object" (that is, an instance of the class java.lang.Object) cannot represent any state apart from its own identity. So what you are asking for is impossible.

On the other hand, all Java classes are implicitly subtypes of java.lang.Object, so any function that takes an Object parameter can be called with a JSONObject instance as argument ... assuming that JSONObject is a concrete Java class.

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