Convert a JSON String into Java Object

Question

i have a String returned by a service, in this JSON format:

String message = {
    "Tickets":
            [{
                    "Type": "type1",
                    "Author": "author1",
                    "Rows":
                            [
                                {
                                    "Price": "100.0",
                                    "Date": "24/06/2016",
                                    "Amount": "10"
                                },
                                {
                                    "Type": "Comment",
                                    "Value": "some comment goes here"
                                }
                            ],
                    "ID": "165"
                }],
    "Desk": "desk1",
    "User": "user1"
}

I need to parse it and convert into a Java object. I tried to create a dom like this:

public class TicketWrapper{
    private Ticket ticket;
    private String desk;
    private String user;
}

public class Ticket {
    private String type;
    private String author;
    private List<Row> rows;
    private String id;
}

public class Row1{
    private float price;
    private Date date;
    private int amount;
}

public class Row2{
    private String type;
    private float value;
}

Then I try to parse it with Google Gson, this way:

TicketWrapper ticket = gson.fromJson(message, TicketWrapper.class)

but if I print it System.out.println(gson.toJson(ticket)), it prints: {"desk" : 0, "user" : 0}

I don't know how to parse that Json into a Java Object, and how to tell him that a row into "Rows" can be of the Row1 type or Row2 type.

In the JSON, the attribute is named "Tickets", with an s, and as the name indicates, it's an array of tickets, and not just a single ticket.It's also unclear what Row is, and how Row1 and Row2 are relevant. — JB Nizet
– JB Nizet, Commented Apr 6, 2016 at 20:49
I suggest you read some tutorials regarding the usage of Gson.fromJson — Pooya
– Pooya, Commented Apr 6, 2016 at 20:59
Thank you, i haven't idea case was important, because as a convention, variable starts with lowercase, but the service returns me variables in uppercase: @SerializedName is the solution! Thank you. — luca89pe
– luca89pe, Commented Apr 7, 2016 at 12:33

halfer · Accepted Answer · 2016-04-11 06:23:15Z

I think there is a few issues, such names of properties in lower case and dateformat and mix types of rows. I just changed like this and worked for me:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.SerializedName;
import org.junit.Test;
import java.util.Date;
import java.util.List;

public class CheckTest {

    @Test
    public void thisTest() {
        Gson gson = new GsonBuilder()
                .setDateFormat("dd-MM-yyyy")
                .setPrettyPrinting()
                .create();
        String message = "{\"Tickets\":" +
                "[{\"Type\":\"type1\"," +
                "\"Author\":\"author1\"," +
                "\"Rows\":[{\"Price\":\"100.0\"," +
                "\"Date\":\"24-06-2016\"," +
                "\"Amount\":\"10\"}," +
                "{\"Type\":\"Comment\"," +
                "\"Value\":\"some comment goes here\"}]," +
                "\"ID\":\"165\"}]," +
                "\"Desk\":\"desk1\"," +
                "\"User\":\"user1\"}";
        TicketWrapper ticket = gson.fromJson(message, TicketWrapper.class);
        System.out.println(ticket.toString());
    }

    public class TicketWrapper {
        @SerializedName("Tickets")
        private List<Ticket> tickets;
        @SerializedName("Desk")
        private String desk;
        @SerializedName("User")
        private String user;
        public TicketWrapper() {
        }
    }

    public class Ticket {
        @SerializedName("Type")
        private String type;
        @SerializedName("Author")
        private String author;
        @SerializedName("Rows")
        private List<Row> rows;
        @SerializedName("ID")
        private String id;

        public Ticket() {
        }
    }

    public class Row {
        @SerializedName("Type")
        private String type;
        @SerializedName("Value")
        private String value;
        @SerializedName("Price")
        private float price;
        @SerializedName("Date")
        private Date date;
        @SerializedName("Amount")
        private int amount;

        public Row() {
        }
    }
}

Thank you, this is what I was looking for! Only a thing, there is a way to tell gson: if row is of type Row1, don't fill fields of Row2, otherwise, if it's Row2, don't fill fields of Row1. I tried by doing some polymorphism like Row1 extends Row and Row2 extends Row, and use: private List<? extends Row> rows but it fill the rows only with the fields of base class. Thank you!

philoniare · Accepted Answer · 2016-04-06 20:53:06Z

1

As others have already mentioned in the comment, you need to make sure the mapping directly reflects the file names. It needs to be 'User' and 'Desk' instead of 'user' and 'desk'. Also, you have a list of tickets, which would map to List Tickets.

answered Apr 6, 2016 at 20:53

philoniare

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