Converting JSON array to POJO using jackson object mapper

Question

This is possibly a duplicate question.. please refer this link.
I am able to map one json object to POJO.But how can i convert array of json object to pojo using the same jackson framework.

private void jsonToPojo(){
   ObjectMapper mapper=new ObjectMapper();

    try {
        User1 user1=mapper.readValue(readFromFile(), User1.class);
        User1[] user2=mapper.readValue(readFromFile(), User1[].class);
        System.out.println(user1);
        Toast.makeText(getApplicationContext(), "inside try", 0).show();
    } catch (JsonParseException e) {
        // TODO Auto-generated catch block
        Log.i("Exception", "jsonparseexception");
        e.printStackTrace();
    } catch (JsonMappingException e) {
        // TODO Auto-generated catch block
        Log.i("Exception", "jsonmapping exception");
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        Log.i("Exception", "ioexception");
        e.printStackTrace();
    }
}

This is the class user object.

public class User {
private int age = 23;
private String name = "amal";
private List<String> messages = new ArrayList<String>() {
    {
        add("hi");
        add("how");
        add("are u.");
    }
};

//getter and setter methods

@Override
public String toString() {
    return "User [age=" + age + ", name=" + name + ", " +
            "messages=" + messages + "]";
}

This is what i tried to do:(readFromFile() takes json from a file)

User1[] user2=mapper.readValue(readFromFile(), User1[].class);

The jsonToPojo() is working well for only one object. However, if i try the above line of code,its not taking the following json:

[ 
 {
   "age":"23",
   "messages":["hi","how","are u."],
   "name":"amal"
 },

 {
   "age":"98",
   "messages":["Reply","my","question"],
   "name":"You"
 }
]

I have tested your example JSON and yours code works for me. Are User and User1 classes same or you have two different classes? — Michał Ziober
– Michał Ziober, Commented May 11, 2013 at 22:35
user1 is a new class. well i want to store the array of json object in the pojo.. thats what i am not able to. — amalBit
– amalBit, Commented May 13, 2013 at 5:16

DennisH · Accepted Answer · 2013-05-13 09:13:52Z

Try something like this:

public class Test {

/**
 * @param args
 */
public static void main(String[] args) {
    User a = new User(23, "amal");
    ArrayList<String> message = new ArrayList<String>();
    message.add("m1");
    message.add("m2");
    a.setMessages(message);

    User b = new User(58, "pete");
    User[] ab = new User[] {a, b};

    ObjectMapper mapper = new ObjectMapper();

    try {
        String s1 = getJson1(a);
        System.out.println(s1);
        User user1 = mapper.readValue(s1, User.class);
        System.out.println(user1);

        System.out.println("----------------");

        String s2 = getJson2(ab);
        System.out.println(s2);
        User[] user2 = mapper.readValue(s2, User[].class);
        for (User u : user2)
            System.out.println(u);

    } catch (Exception e) {
        e.printStackTrace();
    }

}

    private static String getJson1(User user) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(user);
    }

    private static String getJson2(User[] ab) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(ab);
    }

}

public class User {
    private int               age;
    private String            name;
    private ArrayList<String> messages;

    public User() {
        super();
    }

    public User(int age, String name) {
        this();
        this.age = age;
        this.name = name;
    }

    // ****************
    // Getter & Setter ....
    // ****************
}

You will get this Output:

{"age":23,"name":"amal","messages":["m1","m2"]}
User [age=23, name=amal, messages=[m1, m2]]
----------------
[{"age":23,"name":"amal","messages":["m1","m2"]},{"age":58,"name":"pete","messages":null}]
User [age=23, name=amal, messages=[m1, m2]]
User [age=58, name=pete, messages=null]

Thanks, Helped me out as well.. It was as simple as adding the [ ] behind my "user" class in the mapper.readValue... line

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